diff --git a/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.h b/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.h
index 3d5a4dfce0..ae8d4298b4 100644
--- a/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.h
+++ b/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.h
@@ -58,6 +58,16 @@
 @property(nonatomic) PSMProgress progress;
 @property(nonatomic) BOOL isProcessing;
 @property(nonatomic, assign) BOOL isPinned;
+@property(nonatomic, assign) BOOL isGroupHeader;
+@property(nonatomic, assign) BOOL isGroupMember;
+@property(nonatomic, assign) BOOL isGroupCollapsed;
+@property(nonatomic, assign) BOOL isGroupActive;
+@property(nonatomic, assign) BOOL isMultiSelected;
+@property(nonatomic, assign) CGFloat cellAlpha;
+@property(nonatomic, assign) BOOL isAnimatingCollapse;
+@property(nonatomic, copy) NSString *groupName;
+@property(nonatomic, retain) NSColor *groupColor;
+@property(nonatomic, assign) NSInteger groupMemberCount;
 
 // creation/destruction
 - (id)initWithControlView:(PSMTabBarControl *)controlView;
diff --git a/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.m b/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.m
index aeb1bde814..adefac3102 100644
--- a/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.m
+++ b/ThirdParty/PSMTabBarControl/source/PSMTabBarCell.m
@@ -185,7 +185,26 @@ @implementation PSMTabBarCell  {
     NSMutableArray<PSMCachedTitle *> *_subtitleCache;
     NSTrackingArea *_cellTrackingArea;
     NSTrackingArea *_closeButtonTrackingArea;
-}
+    BOOL _isGroupHeader;
+    BOOL _isGroupMember;
+    BOOL _isGroupCollapsed;
+    BOOL _isGroupActive;
+    BOOL _isMultiSelected;
+    CGFloat _cellAlpha;
+    NSString *_groupName;
+    NSColor *_groupColor;
+    NSInteger _groupMemberCount;
+}
+
+@synthesize isGroupHeader = _isGroupHeader;
+@synthesize isGroupMember = _isGroupMember;
+@synthesize isGroupCollapsed = _isGroupCollapsed;
+@synthesize isGroupActive = _isGroupActive;
+@synthesize isMultiSelected = _isMultiSelected;
+@synthesize cellAlpha = _cellAlpha;
+@synthesize groupName = _groupName;
+@synthesize groupColor = _groupColor;
+@synthesize groupMemberCount = _groupMemberCount;
 
 #pragma mark - Creation/Destruction
 
@@ -203,6 +222,15 @@ - (id)initWithControlView:(PSMTabBarControl *)controlView {
         _hasCloseButton = YES;
         _modifierString = [@"" copy];
         _truncationStyle = NSLineBreakByTruncatingTail;
+        _isGroupHeader = NO;
+        _isGroupMember = NO;
+        _isGroupCollapsed = NO;
+        _isGroupActive = NO;
+        _isMultiSelected = NO;
+        _cellAlpha = 1.0;
+        _groupName = nil;
+        _groupColor = nil;
+        _groupMemberCount = 0;
         [self setUpAccessibilityElement];
     }
     return self;
diff --git a/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.h b/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.h
index a8242152df..75b4ed684d 100644
--- a/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.h
+++ b/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.h
@@ -157,6 +157,11 @@ extern PSMTabBarControlOptionKey PSMTabBarControlOptionPUAFontProvider;  // id<P
 - (BOOL)tabViewShouldDragWindow:(NSTabView *)tabView event:(NSEvent *)event;
 - (BOOL)tabViewShouldAllowDragOnAddTabButton:(NSTabView *)tabView;
 - (CGFloat)tabViewDesiredTabBarHeight:(NSTabView *)tabView;
+- (void)tabView:(NSTabView *)tabView didClickGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem;
+- (void)tabView:(NSTabView *)tabView doubleClickGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem;
+- (void)tabView:(NSTabView *)tabView willBeginDraggingGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem;
+- (NSMenu *)tabView:(NSTabView *)tabView menuForGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem;
+- (void)tabView:(NSTabView *)tabView groupTabViewItems:(NSArray<NSTabViewItem *> *)tabViewItems;
 
 @end
 
@@ -230,12 +235,22 @@ extern const CGFloat PSMTabBarProgressBarHeight;
 
 // tab information
 - (NSMutableArray *)representedTabViewItems;
+- (NSMutableArray<PSMTabBarCell *> *)cells;
 - (int)numberOfVisibleTabs;
 
 // special effects
 - (void)hideTabBar:(BOOL)hide animate:(BOOL)animate;
+- (void)update;
+- (void)update:(BOOL)animate;
+- (void)markNextInsertionsAsAnimated:(NSInteger)count;
+- (void)beginCollapseAnimationForTabViewItems:(NSArray<NSTabViewItem *> *)items completion:(void (^)(void))completion;
+- (void)cancelCollapseAnimation;
 - (BOOL)isTabBarHidden;
 
+// Frame of the cell displaying the given tab view item, in the receiver's
+// coordinate system. Returns NSZeroRect if no cell currently shows the item.
+- (NSRect)frameOfCellForTabViewItem:(NSTabViewItem *)item;
+
 // internal bindings methods also used by the tab drag assistant
 - (void)bindPropertiesForCell:(PSMTabBarCell *)cell andTabViewItem:(NSTabViewItem *)item;
 - (void)removeTabForCell:(PSMTabBarCell *)cell;
@@ -245,6 +260,7 @@ extern const CGFloat PSMTabBarProgressBarHeight;
 // Internal inset. Ensures nothing but background is drawn in this are.
 @property(nonatomic, assign) NSEdgeInsets insets;
 @property(nonatomic) CGFloat height;
+@property(nonatomic, assign) BOOL lastDragWasGroupHeader;
 
 - (void)setTabColor:(nullable NSColor *)aColor forTabViewItem:(NSTabViewItem *) tabViewItem;
 - (nullable NSColor*)tabColorForTabViewItem:(NSTabViewItem*)tabViewItem;
diff --git a/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.m b/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.m
index 03b1341789..86646c2bfd 100644
--- a/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.m
+++ b/ThirdParty/PSMTabBarControl/source/PSMTabBarControl.m
@@ -142,6 +142,112 @@ - (BOOL)isEqual:(id)object {
 
 @end
 
+// Minimal pill button used for the multi-select "Group (N)" action.
+@interface PSMGroupPillButton : NSView
+@property (nonatomic, copy) NSString *title;
+@property (nonatomic, weak) id target;
+@property (nonatomic, assign) SEL action;
+@end
+
+@implementation PSMGroupPillButton {
+    NSTrackingArea *_trackingArea;
+    BOOL _hovered;
+    BOOL _pressed;
+}
+
+- (instancetype)init {
+    self = [super initWithFrame:NSZeroRect];
+    if (self) {
+        self.wantsLayer = NO;
+    }
+    return self;
+}
+
+- (void)dealloc {
+    [_trackingArea release];
+    [_title release];
+    [super dealloc];
+}
+
+- (void)updateTrackingAreas {
+    [super updateTrackingAreas];
+    if (_trackingArea) {
+        [self removeTrackingArea:_trackingArea];
+        [_trackingArea release];
+    }
+    _trackingArea = [[NSTrackingArea alloc] initWithRect:self.bounds
+                                                 options:NSTrackingMouseEnteredAndExited | NSTrackingActiveInKeyWindow
+                                                   owner:self
+                                                userInfo:nil];
+    [self addTrackingArea:_trackingArea];
+}
+
+- (NSSize)intrinsicContentSize {
+    NSFont *font = [NSFont systemFontOfSize:11.0 weight:NSFontWeightMedium];
+    NSSize textSize = [_title sizeWithAttributes:@{NSFontAttributeName: font}];
+    return NSMakeSize(textSize.width + 20.0, 20.0);
+}
+
+- (BOOL)hasDarkAppearance {
+    NSAppearanceName bestMatch =
+        [self.effectiveAppearance bestMatchFromAppearancesWithNames:@[ NSAppearanceNameDarkAqua,
+                                                                       NSAppearanceNameVibrantDark,
+                                                                       NSAppearanceNameAqua,
+                                                                       NSAppearanceNameVibrantLight ]];
+    return ([bestMatch isEqualToString:NSAppearanceNameDarkAqua] ||
+            [bestMatch isEqualToString:NSAppearanceNameVibrantDark]);
+}
+
+- (void)drawRect:(NSRect)dirtyRect {
+    NSRect r = NSInsetRect(self.bounds, 0.5, 0.5);
+    CGFloat radius = NSHeight(r) / 2.0;
+    NSBezierPath *pill = [NSBezierPath bezierPathWithRoundedRect:r xRadius:radius yRadius:radius];
+    const BOOL dark = [self hasDarkAppearance];
+    const CGFloat foregroundWhite = dark ? 1.0 : 0.0;
+    const CGFloat borderWhite = dark ? 0.85 : 0.15;
+
+    // Fill: transparent normally, subtle tint on hover/press.
+    if (_pressed) {
+        [[NSColor colorWithWhite:foregroundWhite alpha:0.12] setFill];
+        [pill fill];
+    } else if (_hovered) {
+        [[NSColor colorWithWhite:foregroundWhite alpha:0.07] setFill];
+        [pill fill];
+    }
+
+    // Border.
+    CGFloat borderAlpha = _hovered ? 0.5 : 0.28;
+    [[NSColor colorWithWhite:borderWhite alpha:borderAlpha] setStroke];
+    [pill setLineWidth:1.0];
+    [pill stroke];
+
+    // Label.
+    CGFloat textAlpha = _hovered ? 1.0 : 0.72;
+    NSDictionary *attrs = @{
+        NSFontAttributeName: [NSFont systemFontOfSize:11.0 weight:NSFontWeightMedium],
+        NSForegroundColorAttributeName: [NSColor colorWithWhite:foregroundWhite alpha:textAlpha]
+    };
+    NSSize ts = [_title sizeWithAttributes:attrs];
+    [_title drawAtPoint:NSMakePoint(NSMidX(self.bounds) - ts.width / 2.0,
+                                    NSMidY(self.bounds) - ts.height / 2.0)
+         withAttributes:attrs];
+}
+
+- (void)mouseEntered:(NSEvent *)event { _hovered = YES;  [self setNeedsDisplay:YES]; }
+- (void)mouseExited:(NSEvent *)event  { _hovered = NO; _pressed = NO; [self setNeedsDisplay:YES]; }
+- (void)mouseDown:(NSEvent *)event    { _pressed = YES;  [self setNeedsDisplay:YES]; }
+- (void)mouseUp:(NSEvent *)event {
+    _pressed = NO;
+    [self setNeedsDisplay:YES];
+    if (NSMouseInRect([self convertPoint:event.locationInWindow fromView:nil], self.bounds, self.isFlipped)) {
+        if (_target && _action) {
+            [NSApp sendAction:_action to:_target from:self];
+        }
+    }
+}
+
+@end
+
 @interface PSMTabBarControl ()<PSMTabBarControlProtocol, NSMenuItemValidation, NSViewToolTipOwner>
 - (void)removeTabProgressBarForCell:(PSMTabBarCell *)cell;
 @end
@@ -154,7 +260,22 @@ @implementation PSMTabBarControl {
 
     // drawing style
     NSTimer *_animationTimer;
-    float _animationDelta;
+    NSArray<NSNumber *> *_animationStartWidths; // cell widths captured when the resize animation began
+    NSTimeInterval _animationStartTime;
+
+    // fade-in / slide-in animation for new cells (group expand only)
+    NSMutableSet<PSMTabBarCell *> *_fadingInCells;
+    NSTimer *_fadeTimer;
+    NSInteger _animatedInsertionCount;
+
+    // slide-out / fade-out animation for collapsing cells (group collapse)
+    NSMutableSet<PSMTabBarCell *> *_collapsingCells;
+    NSTimer *_collapseTimer;
+    NSMutableArray<void (^)(void)> *_collapseCompletions;
+
+    // deferred single-click on group headers (to avoid firing toggle on double-click)
+    NSTimer *_groupHeaderSingleClickTimer;
+    PSMTabBarCell *_pendingGroupHeaderClickCell;
 
     // vertical tab resizing
     BOOL _resizing;
@@ -184,6 +305,10 @@ @implementation PSMTabBarControl {
     NSMapTable<PSMTabBarCell *, NSView *> *_tabProgressBars;
     NSMutableArray<PSMToolTip *> *_tooltips;
     NSInteger _toolTipCoalescing;
+
+    // multi-selection (cmd+click)
+    NSMutableSet<NSTabViewItem *> *_multiSelectedTabViewItems;
+    PSMGroupPillButton *_groupSelectionButton;
 }
 
 #pragma mark -
@@ -371,6 +496,9 @@ - (void)setupButtons {
 }
 
 - (void)dealloc {
+    [_fadeTimer invalidate];
+    [_collapseTimer invalidate];
+    [_groupHeaderSingleClickTimer invalidate];
     [[NSNotificationCenter defaultCenter] removeObserver:self];
 
     // Remove bindings.
@@ -396,6 +524,12 @@ - (void)dealloc {
     [_style release];
     [_tooltips release];
     _tooltips = nil;
+    [_animationStartWidths release];
+    [_fadingInCells release];
+    [_collapsingCells release];
+    [_collapseCompletions release];
+    [_multiSelectedTabViewItems release];
+    [_groupSelectionButton release];
 
     [self unregisterDraggedTypes];
 
@@ -702,6 +836,23 @@ - (void)addTabViewItem:(NSTabViewItem *)item atIndex:(NSUInteger)i {
     // add to collection
     [_cells insertObject:cell atIndex:i];
 
+    // Only animate group-expand insertions; regular new tabs appear instantly.
+    if (_animatedInsertionCount > 0) {
+        _animatedInsertionCount--;
+        cell.cellAlpha = 0.0;
+        if (!_fadingInCells) {
+            _fadingInCells = [[NSMutableSet alloc] init];
+        }
+        [_fadingInCells addObject:cell];
+        if (!_fadeTimer) {
+            _fadeTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 / 60.0
+                                                         target:self
+                                                       selector:@selector(_tickFadeIn:)
+                                                       userInfo:nil
+                                                        repeats:YES];
+        }
+    }
+
     // bind it up
     [self initializeStateForCell:cell];
     [self bindPropertiesForCell:cell andTabViewItem:item];
@@ -713,6 +864,9 @@ - (void)addTabViewItem:(NSTabViewItem *)item {
 }
 
 - (void)removeTabForCell:(PSMTabBarCell *)cell {
+    if (!cell) {
+        return;
+    }
     // unbind
     [cell unbind:@"title"];
 
@@ -731,6 +885,7 @@ - (void)removeTabForCell:(PSMTabBarCell *)cell {
 
     // pull from collection
     [_cells removeObject:cell];
+    [_fadingInCells removeObject:cell];
 }
 
 - (BOOL)shouldShowCustomProgressBarForTabCell:(PSMTabBarCell *)cell {
@@ -1163,6 +1318,118 @@ - (void)update {
     [self update:NO];
 }
 
+- (void)markNextInsertionsAsAnimated:(NSInteger)count {
+    _animatedInsertionCount += count;
+}
+
+- (void)beginCollapseAnimationForTabViewItems:(NSArray<NSTabViewItem *> *)items
+                                   completion:(void (^)(void))completion {
+    if (!_collapsingCells) {
+        _collapsingCells = [[NSMutableSet alloc] init];
+    }
+    for (NSTabViewItem *item in items) {
+        for (PSMTabBarCell *cell in _cells) {
+            if ([cell.representedObject isEqual:item]) {
+                cell.cellAlpha = 1.0;
+                [_collapsingCells addObject:cell];
+                break;
+            }
+        }
+    }
+    if (!_collapseCompletions) {
+        _collapseCompletions = [[NSMutableArray alloc] init];
+    }
+    if (completion) {
+        [_collapseCompletions addObject:[[completion copy] autorelease]];
+    }
+    if (!_collapseTimer) {
+        _collapseTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 / 60.0
+                                                         target:self
+                                                       selector:@selector(_tickCollapse:)
+                                                       userInfo:nil
+                                                        repeats:YES];
+    }
+}
+
+- (void)cancelCollapseAnimation {
+    [_collapseTimer invalidate];
+    _collapseTimer = nil;
+    for (PSMTabBarCell *cell in _collapsingCells) {
+        cell.cellAlpha = 1.0;
+    }
+    [_collapsingCells removeAllObjects];
+    NSArray<void (^)(void)> *completions = [[_collapseCompletions copy] autorelease];
+    [_collapseCompletions removeAllObjects];
+    for (void (^cb)(void) in completions) { cb(); }
+}
+
+- (NSRect)frameOfCellForTabViewItem:(NSTabViewItem *)item {
+    for (PSMTabBarCell *cell in _cells) {
+        if ([cell.representedObject isEqual:item]) {
+            return cell.frame;
+        }
+    }
+    return NSZeroRect;
+}
+
+- (void)_fireGroupHeaderSingleClick:(NSTimer *)timer {
+    _groupHeaderSingleClickTimer = nil;
+    PSMTabBarCell *cell = _pendingGroupHeaderClickCell;
+    _pendingGroupHeaderClickCell = nil;
+    if (cell) {
+        [self tabClick:cell];
+    }
+}
+
+- (void)_tickCollapse:(NSTimer *)timer {
+    const CGFloat delta = (1.0 / 60.0) / 0.12;  // 120ms total — collapse faster than expand
+    NSMutableSet *completed = [NSMutableSet set];
+    for (PSMTabBarCell *cell in _collapsingCells) {
+        cell.isAnimatingCollapse = YES;
+        cell.cellAlpha = MAX(0.0, cell.cellAlpha - delta);
+        if (cell.cellAlpha <= 0.0) {
+            [completed addObject:cell];
+        }
+    }
+    for (PSMTabBarCell *cell in completed) {
+        cell.isAnimatingCollapse = NO;
+    }
+    [_collapsingCells minusSet:completed];
+    if ([PSMTabBarControl isAnyDragInProgress]) {
+        [self setNeedsDisplay:YES];
+    } else {
+        [self update];
+    }
+    if (_collapsingCells.count == 0) {
+        [timer invalidate];
+        _collapseTimer = nil;
+        NSArray<void (^)(void)> *completions = [[_collapseCompletions copy] autorelease];
+        [_collapseCompletions removeAllObjects];
+        for (void (^cb)(void) in completions) { cb(); }
+    }
+}
+
+- (void)_tickFadeIn:(NSTimer *)timer {
+    const CGFloat delta = (1.0 / 60.0) / 0.25;  // 250ms total — expand
+    NSMutableSet *completed = [NSMutableSet set];
+    for (PSMTabBarCell *cell in _fadingInCells) {
+        cell.cellAlpha = MIN(1.0, cell.cellAlpha + delta);
+        if (cell.cellAlpha >= 1.0) {
+            [completed addObject:cell];
+        }
+    }
+    [_fadingInCells minusSet:completed];
+    if (_fadingInCells.count == 0) {
+        [timer invalidate];
+        _fadeTimer = nil;
+    }
+    if ([PSMTabBarControl isAnyDragInProgress]) {
+        [self setNeedsDisplay:YES];
+    } else {
+        [self update];
+    }
+}
+
 - (void)setFrame:(NSRect)frame {
     [super setFrame:frame];
     [self syncTabProgressBars];
@@ -1268,8 +1535,14 @@ - (void)reallyUpdate:(BOOL)animate {
                 [_animationTimer invalidate];
             }
             
-            _animationDelta = 0.0f;
-            _animationTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 / 30.0
+            NSMutableArray<NSNumber *> *startWidths = [NSMutableArray arrayWithCapacity:cellCount];
+            for (PSMTabBarCell *cell in _cells) {
+                [startWidths addObject:@(cell.frame.size.width)];
+            }
+            [_animationStartWidths release];
+            _animationStartWidths = [startWidths copy];
+            _animationStartTime = [NSDate timeIntervalSinceReferenceDate];
+            _animationTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 / 60.0
                                                                target:self
                                                              selector:@selector(_animateCells:)
                                                              userInfo:[self cellWidthsForHorizontalArrangementWithOverflow:_lainOutWithOverflow]
@@ -1341,6 +1614,8 @@ - (CGFloat)totalPinnedSpaceForPinnedCount:(NSUInteger)pinnedCount unpinnedCount:
         CGFloat width;
         if (cell.isPinned) {
             width = _pinnedTabWidth;
+        } else if (cell.isGroupHeader) {
+            width = [cell desiredWidthOfCell];
         } else {
             width = MAX(_cellMinWidth, MIN([cell desiredWidthOfCell], _cellMaxWidth));
         }
@@ -1363,11 +1638,14 @@ - (CGFloat)totalPinnedSpaceForPinnedCount:(NSUInteger)pinnedCount unpinnedCount:
 - (BOOL)shouldUseOptimalWidthWithOverflow:(BOOL)withOverflow {
     const CGFloat availableWidth = [self availableCellWidthWithOverflow:withOverflow];
     const NSUInteger pinnedCount = [self numberOfPinnedCells];
-    const NSUInteger unpinnedCount = _cells.count - pinnedCount;
-    const CGFloat pinnedSpace = [self totalPinnedSpaceForPinnedCount:pinnedCount unpinnedCount:unpinnedCount];
+    const CGFloat pinnedSpace = [self totalPinnedSpaceForPinnedCount:pinnedCount unpinnedCount:_cells.count - pinnedCount];
     const CGFloat unpinnedAvailable = availableWidth - pinnedSpace;
-    BOOL canFitAllCellsOptimally = (self.cellOptimumWidth * unpinnedCount <= unpinnedAvailable);
-    return !self.stretchCellsToFit && canFitAllCellsOptimally;
+    CGFloat totalUnpinnedDesiredWidth = 0;
+    for (PSMTabBarCell *c in _cells) {
+        if (c.isPinned) { continue; }
+        totalUnpinnedDesiredWidth += c.isGroupHeader ? [c desiredWidthOfCell] : self.cellOptimumWidth;
+    }
+    return !self.stretchCellsToFit && (totalUnpinnedDesiredWidth <= unpinnedAvailable);
 }
 
 - (NSArray<NSNumber *> *)cellWidthsForHorizontalArrangementWithOverflow:(BOOL)withOverflow {
@@ -1388,8 +1666,9 @@ - (BOOL)shouldUseOptimalWidthWithOverflow:(BOOL)withOverflow {
         // No pinned cells
         NSMutableArray<NSNumber *> *newWidths = [NSMutableArray array];
         if ([self shouldUseOptimalWidthWithOverflow:withOverflow]) {
-            for (int i = 0; i < cellCount; i++) {
-                [newWidths addObject:@(_cellOptimumWidth)];
+            for (PSMTabBarCell *c in _cells) {
+                CGFloat w = c.isGroupHeader ? [c desiredWidthOfCell] : _cellOptimumWidth;
+                [newWidths addObject:@(w)];
             }
         } else {
             const BOOL canFitAllCellsMinimally = (self.cellMinWidth * cellCount + intercellSpacing * MAX(0, (cellCount - 1)) <= availableWidth);
@@ -1402,11 +1681,11 @@ - (BOOL)shouldUseOptimalWidthWithOverflow:(BOOL)withOverflow {
                     numberOfVisibleCells -= 1;
                 }
             }
-            [self computeCellFramesInContainerOfWidth:availableWidth
-                                 numberOfVisibleCells:numberOfVisibleCells
-                                     intercellSpacing:intercellSpacing
-                                                scale:2.0
-                                               frames:newWidths];
+            [self computeCompressedWidthsForCells:_cells
+                                            count:numberOfVisibleCells
+                                   containerWidth:availableWidth
+                                 intercellSpacing:intercellSpacing
+                                           frames:newWidths];
         }
         return newWidths;
     }
@@ -1421,8 +1700,10 @@ - (BOOL)shouldUseOptimalWidthWithOverflow:(BOOL)withOverflow {
     if (unpinnedCount > 0 && unpinnedContainerWidth > 0) {
         if ([self shouldUseOptimalWidthWithOverflow:withOverflow]) {
             numberOfVisibleUnpinned = unpinnedCount;
-            for (NSUInteger i = 0; i < unpinnedCount; i++) {
-                [unpinnedWidths addObject:@(_cellOptimumWidth)];
+            for (PSMTabBarCell *c in _cells) {
+                if (c.isPinned) { continue; }
+                CGFloat w = c.isGroupHeader ? [c desiredWidthOfCell] : _cellOptimumWidth;
+                [unpinnedWidths addObject:@(w)];
             }
         } else {
             const BOOL canFitAllUnpinned = (self.cellMinWidth * unpinnedCount +
@@ -1438,11 +1719,15 @@ - (BOOL)shouldUseOptimalWidthWithOverflow:(BOOL)withOverflow {
                 numberOfVisibleUnpinned = MAX(0, numberOfVisibleUnpinned);
             }
             if (numberOfVisibleUnpinned > 0) {
-                [self computeCellFramesInContainerOfWidth:unpinnedContainerWidth
-                                     numberOfVisibleCells:numberOfVisibleUnpinned
-                                         intercellSpacing:intercellSpacing
-                                                    scale:2.0
-                                                   frames:unpinnedWidths];
+                NSMutableArray<PSMTabBarCell *> *unpinnedCells = [NSMutableArray array];
+                for (PSMTabBarCell *c in _cells) {
+                    if (!c.isPinned) { [unpinnedCells addObject:c]; }
+                }
+                [self computeCompressedWidthsForCells:unpinnedCells
+                                                count:numberOfVisibleUnpinned
+                                       containerWidth:unpinnedContainerWidth
+                                     intercellSpacing:intercellSpacing
+                                               frames:unpinnedWidths];
             }
         }
     }
@@ -1472,6 +1757,34 @@ - (BOOL)shouldUseOptimalWidthWithOverflow:(BOOL)withOverflow {
     return result;
 }
 
+- (void)computeCompressedWidthsForCells:(NSArray<PSMTabBarCell *> *)cells
+                                  count:(NSInteger)n
+                         containerWidth:(CGFloat)containerWidth
+                       intercellSpacing:(CGFloat)intercellSpacing
+                                 frames:(NSMutableArray<NSNumber *> *)outWidths {
+    CGFloat groupHeaderTotal = 0;
+    NSInteger regularCount = 0;
+    NSInteger i = 0;
+    for (PSMTabBarCell *c in cells) {
+        if (i >= n) break;
+        if (c.isGroupHeader) {
+            groupHeaderTotal += [c desiredWidthOfCell];
+        } else {
+            regularCount++;
+        }
+        i++;
+    }
+    const CGFloat totalSpacing = (n > 1) ? (n - 1) * intercellSpacing : 0;
+    const CGFloat remaining = MAX(0, containerWidth - groupHeaderTotal - totalSpacing);
+    const CGFloat regularWidth = regularCount > 0 ? floor(remaining / regularCount) : 0;
+    i = 0;
+    for (PSMTabBarCell *c in cells) {
+        if (i >= n) break;
+        [outWidths addObject:c.isGroupHeader ? @([c desiredWidthOfCell]) : @(regularWidth)];
+        i++;
+    }
+}
+
 - (void)computeCellFramesInContainerOfWidth:(CGFloat)containerWidth
                        numberOfVisibleCells:(NSInteger)n
                            intercellSpacing:(CGFloat)intercellSpacing
@@ -1525,48 +1838,37 @@ - (void)_removeCellTrackingRects {
 
 - (void)_animateCells:(NSTimer *)timer {
     NSArray *targetWidths = [timer userInfo];
-    int i, numberOfVisibleCells = [targetWidths count];
-    float totalChange = 0.0f;
-    BOOL updated = NO;
+    const NSInteger numberOfVisibleCells = [targetWidths count];
+    const NSTimeInterval duration = 0.25;
+    const NSTimeInterval elapsed = [NSDate timeIntervalSinceReferenceDate] - _animationStartTime;
+    const CGFloat progress = MIN(1.0, elapsed / duration);
+    const CGFloat eased = 1.0 - pow(1.0 - progress, 3.0);
+
+    CGFloat totalChange = 0.0;
+    NSInteger i = 0;
+    for (PSMTabBarCell *currentCell in _cells) {
+        NSRect cellFrame = [currentCell frame];
+        cellFrame.origin.x += totalChange;
 
-    if ([_cells count] > 0) {
-        //compare our target widths with the current widths and move towards the target
-        for (i = 0; i < [_cells count]; i++) {
-            PSMTabBarCell *currentCell = [_cells objectAtIndex:i];
-            NSRect cellFrame = [currentCell frame];
-            cellFrame.origin.x += totalChange;
-
-            if (i < numberOfVisibleCells) {
-                float target = [[targetWidths objectAtIndex:i] floatValue];
-
-                if (currentCell.isPinned) {
-                    // Pinned cells snap to target width immediately - no gradual animation.
-                    totalChange += target - cellFrame.size.width;
-                    cellFrame.size.width = target;
-                    [currentCell setFrame:cellFrame];
-                } else if (fabs(cellFrame.size.width - target) < _animationDelta) {
-                    cellFrame.size.width = target;
-                    totalChange += cellFrame.size.width - target;
-                    [currentCell setFrame:cellFrame];
-                } else if (cellFrame.size.width > target) {
-                    cellFrame.size.width -= _animationDelta;
-                    totalChange -= _animationDelta;
-                    updated = YES;
-                } else if (cellFrame.size.width < target) {
-                    cellFrame.size.width += _animationDelta;
-                    totalChange += _animationDelta;
-                    [currentCell setFrame:cellFrame];
-                    updated = YES;
-                }
+        if (i < numberOfVisibleCells) {
+            const CGFloat target = [[targetWidths objectAtIndex:i] doubleValue];
+            CGFloat newWidth;
+            if (currentCell.isPinned || i >= (NSInteger)_animationStartWidths.count) {
+                // Pinned cells snap to target width immediately - no gradual animation.
+                newWidth = target;
+            } else {
+                const CGFloat start = [_animationStartWidths[i] doubleValue];
+                newWidth = start + (target - start) * eased;
             }
-
-            [currentCell setFrame:cellFrame];
+            totalChange += newWidth - cellFrame.size.width;
+            cellFrame.size.width = newWidth;
         }
 
-        _animationDelta += 4.0f;
+        [currentCell setFrame:cellFrame];
+        i++;
     }
 
-    if (!updated) {
+    if (progress >= 1.0) {
         [self finishUpdateWithRegularWidths:targetWidths
                          widthsWithOverflow:targetWidths];
         [timer invalidate];
@@ -1626,8 +1928,19 @@ - (NSMenu *)_setupCells:(NSArray *)newValues {
         int tabState = 0;
         if (i < numberOfVisibleCells) {
             // set cell frame
+            const CGFloat fullCellWidth = [[newValues objectAtIndex:i] floatValue];
+            CGFloat animCellWidth;
+            if (cell.cellAlpha >= 1.0) {
+                animCellWidth = fullCellWidth;
+            } else {
+                const CGFloat t = cell.cellAlpha;
+                const CGFloat easedT = [_collapsingCells containsObject:cell]
+                    ? t * t * t                      // easeInCubic — accelerates into collapse
+                    : 1.0 - pow(1.0 - t, 3.0);      // easeOutCubic — decelerates into expansion
+                animCellWidth = fullCellWidth * easedT;
+            }
             if ([self orientation] == PSMTabBarHorizontalOrientation) {
-                cellRect.size.width = [[newValues objectAtIndex:i] floatValue];
+                cellRect.size.width = animCellWidth;
             } else {
                 cellRect.size.width = [self frame].size.width;
                 cellRect.origin.y = [[newValues objectAtIndex:i] floatValue];
@@ -1708,7 +2021,7 @@ - (NSMenu *)_setupCells:(NSArray *)newValues {
             }
 
             // next...
-            cellRect.origin.x += [[newValues objectAtIndex:i] floatValue] + intercellSpacing;
+            cellRect.origin.x += animCellWidth + intercellSpacing;
 
         } else {
             // set up menu items
@@ -1843,14 +2156,16 @@ - (void)mouseDown:(NSEvent *)theEvent {
             if ([theEvent clickCount] == 1) {
                 const NSEventModifierFlags mask = NSEventModifierFlagOption;
                 if (_selectsTabsOnMouseDown && (theEvent.modifierFlags & mask) == 0) {
-                    if (cell.state != NSControlStateValueOn) {
-                        _preDragSelectedTabIndex = [[self tabView] indexOfTabViewItem:self.tabView.selectedTabViewItem];
-                    } else {
-                        // Because we always want it to switch tabs, don't save
-                        // the index if you're dragging the current tab.
-                        _preDragSelectedTabIndex = NSNotFound;
+                    // Skip group headers on mouseDown — they need to wait for mouseUp to
+                    // distinguish a single-click toggle from a double-click rename.
+                    if (![[cell.representedObject identifier] isKindOfClass:[iTermTabGroup class]]) {
+                        if (cell.state != NSControlStateValueOn) {
+                            _preDragSelectedTabIndex = [[self tabView] indexOfTabViewItem:self.tabView.selectedTabViewItem];
+                        } else {
+                            _preDragSelectedTabIndex = NSNotFound;
+                        }
+                        [self tabClick:cell];
                     }
-                    [self tabClick:cell];
                 }
             }
         }
@@ -1933,10 +2248,16 @@ - (void)mouseDragged:(NSEvent *)theEvent {
         float dy = fabs(currentPoint.y - trackingStartPoint.y);
         float distance = sqrt(dx * dx + dy * dy);
 
-        if (distance >= self.minimumTabDragDistance && !_didDrag && ![[PSMTabDragAssistant sharedDragAssistant] isDragging] &&
+        if (distance >= self.minimumTabDragDistance && !_didDrag &&
+                ![[PSMTabDragAssistant sharedDragAssistant] isDragging] &&
                 [[self delegate] respondsToSelector:@selector(tabView:shouldDragTabViewItem:fromTabBar:)] &&
                 [[self delegate] tabView:_tabView shouldDragTabViewItem:[cell representedObject] fromTabBar:self]) {
             _didDrag = YES;
+            self.lastDragWasGroupHeader = cell.isGroupHeader;
+            if (cell.isGroupHeader &&
+                [[self delegate] respondsToSelector:@selector(tabView:willBeginDraggingGroupHeaderTabViewItem:)]) {
+                [[self delegate] tabView:_tabView willBeginDraggingGroupHeaderTabViewItem:[cell representedObject]];
+            }
             ILog(@"Start dragging with mouse down event %@ in window %p with frame %@", [self lastMouseDownEvent], self.window, NSStringFromRect(self.window.frame));
             [[PSMTabDragAssistant sharedDragAssistant] startDraggingCell:cell fromTabBar:self withMouseDownEvent:[self lastMouseDownEvent]];
         }
@@ -2008,10 +2329,31 @@ - (void)handleMouseUp:(NSEvent * _Nonnull)theEvent {
         [mouseDownCell setCloseButtonPressed:NO];
         switch (theEvent.clickCount) {
             case 1:
+                if (_selectsTabsOnMouseDown && (theEvent.modifierFlags & NSEventModifierFlagCommand) != 0) {
+                    // Cmd+click multi-select was already handled on mouse-down; skip to avoid double-toggle.
+                    return;
+                }
+                if (cell.isGroupHeader) {
+                    // Defer: if a second click arrives before doubleClickInterval, the timer is
+                    // cancelled in case 2 so a double-click toggles collapse instead of opening
+                    // the management popover that a lone single-click would.
+                    [_groupHeaderSingleClickTimer invalidate];
+                    _pendingGroupHeaderClickCell = cell;
+                    _groupHeaderSingleClickTimer =
+                        [NSTimer scheduledTimerWithTimeInterval:[NSEvent doubleClickInterval]
+                                                         target:self
+                                                       selector:@selector(_fireGroupHeaderSingleClick:)
+                                                       userInfo:nil
+                                                        repeats:NO];
+                    return;
+                }
                 [self tabClick:cell];
                 return;
 
             case 2:
+                [_groupHeaderSingleClickTimer invalidate];
+                _groupHeaderSingleClickTimer = nil;
+                _pendingGroupHeaderClickCell = nil;
                 [self tabDoubleClick:cell];
                 return;
 
@@ -2028,12 +2370,30 @@ - (void)handleMouseUp:(NSEvent * _Nonnull)theEvent {
 - (NSMenu *)menuForEvent:(NSEvent *)event
 {
     NSMenu *menu = nil;
-    NSTabViewItem *item = [[self cellForPoint:[self convertPoint:[event locationInWindow] fromView:nil] cellFrame:nil] representedObject];
+    PSMTabBarCell *cell = [self cellForPoint:[self convertPoint:[event locationInWindow] fromView:nil] cellFrame:nil];
+    NSTabViewItem *item = [cell representedObject];
+
+    if (item && cell.isGroupHeader) {
+        if ([[self delegate] respondsToSelector:@selector(tabView:menuForGroupHeaderTabViewItem:)]) {
+            menu = [[self delegate] tabView:_tabView menuForGroupHeaderTabViewItem:item];
+        }
+        return menu;
+    }
 
     if (item && [[self delegate] respondsToSelector:@selector(tabView:menuForTabViewItem:)]) {
         menu = [[self delegate] tabView:_tabView menuForTabViewItem:item];
     }
-    else if (!item) {
+
+    if (_multiSelectedTabViewItems.count > 1 && menu) {
+        [menu addItem:[NSMenuItem separatorItem]];
+        NSString *title = [NSString stringWithFormat:@"Group %lu Selected Tabs", (unsigned long)_multiSelectedTabViewItems.count];
+        NSMenuItem *groupItem = [[NSMenuItem alloc] initWithTitle:title action:@selector(groupMultiSelectedTabs:) keyEquivalent:@""];
+        groupItem.target = self;
+        groupItem.representedObject = [_multiSelectedTabViewItems copy];
+        [menu addItem:groupItem];
+    }
+
+    if (!item) {
         // when the "LSUIElement hack" (issue #954) is enabled, the menu bar is inaccessible,
         // so show it as a context menu when right-clicking empty tabBar region
         if ([[[NSBundle mainBundle] infoDictionary] objectForKey:@"LSUIElement"]) {
@@ -2233,7 +2593,10 @@ - (void)draggingSession:(NSDraggingSession *)session endedAtPoint:(NSPoint)aPoin
 
     _haveInitialDragLocation = NO;
     if (operation != NSDragOperationNone) {
-        [self removeTabForCell:[[PSMTabDragAssistant sharedDragAssistant] draggedCell]];
+        PSMTabBarCell *cell = [[PSMTabDragAssistant sharedDragAssistant] draggedCell];
+        if (cell) {
+            [self removeTabForCell:cell];
+        }
         [[PSMTabDragAssistant sharedDragAssistant] finishDrag];
     } else {
         [[PSMTabDragAssistant sharedDragAssistant] draggedImageEndedAt:aPoint operation:operation];
@@ -2266,7 +2629,83 @@ - (void)closeTabClick:(id)sender button:(int)button {
     }
 }
 
+- (void)_updateGroupSelectionButton {
+    const NSUInteger count = _multiSelectedTabViewItems.count;
+    if (count < 2) {
+        _groupSelectionButton.hidden = YES;
+        return;
+    }
+    if (!_groupSelectionButton) {
+        _groupSelectionButton = [[PSMGroupPillButton alloc] init];
+        _groupSelectionButton.target = self;
+        _groupSelectionButton.action = @selector(_groupSelectionButtonClicked:);
+        [self addSubview:_groupSelectionButton];
+    }
+    _groupSelectionButton.title = [NSString stringWithFormat:@"Group (%lu)", (unsigned long)count];
+    NSSize s = _groupSelectionButton.intrinsicContentSize;
+    const CGFloat margin = 6.0;
+    NSRect b = self.bounds;
+    _groupSelectionButton.frame = NSMakeRect(NSMaxX(b) - s.width - margin,
+                                              NSMidY(b) - s.height / 2.0,
+                                              s.width, s.height);
+    _groupSelectionButton.hidden = NO;
+    [_groupSelectionButton setNeedsDisplay:YES];
+}
+
+- (void)_groupSelectionButtonClicked:(id)sender {
+    if (_multiSelectedTabViewItems.count < 2) { return; }
+    NSSet *items = [_multiSelectedTabViewItems copy];
+    if ([[self delegate] respondsToSelector:@selector(tabView:groupTabViewItems:)]) {
+        [[self delegate] tabView:_tabView groupTabViewItems:[items allObjects]];
+    }
+    [self clearMultiSelection];
+}
+
+- (void)clearMultiSelection {
+    for (PSMTabBarCell *cell in _cells) {
+        cell.isMultiSelected = NO;
+    }
+    [_multiSelectedTabViewItems removeAllObjects];
+    _groupSelectionButton.hidden = YES;
+    [self setNeedsDisplay:YES];
+}
+
+- (void)groupMultiSelectedTabs:(NSMenuItem *)sender {
+    NSSet<NSTabViewItem *> *items = sender.representedObject;
+    if (!items || items.count < 2) { return; }
+    if ([[self delegate] respondsToSelector:@selector(tabView:groupTabViewItems:)]) {
+        [[self delegate] tabView:_tabView groupTabViewItems:[items allObjects]];
+    }
+    [self clearMultiSelection];
+}
+
 - (void)tabClick:(id)sender {
+    PSMTabBarCell *cell = sender;
+    NSTabViewItem *clickedItem = [cell representedObject];
+    if ([[clickedItem identifier] isKindOfClass:[iTermTabGroup class]]) {
+        if ([[self delegate] respondsToSelector:@selector(tabView:didClickGroupHeaderTabViewItem:)]) {
+            [[self delegate] tabView:_tabView didClickGroupHeaderTabViewItem:clickedItem];
+        }
+        return;
+    }
+
+    const BOOL cmdHeld = ([NSApp currentEvent].modifierFlags & NSEventModifierFlagCommand) != 0;
+    if (cmdHeld) {
+        if (!_multiSelectedTabViewItems) {
+            _multiSelectedTabViewItems = [[NSMutableSet alloc] init];
+        }
+        if ([_multiSelectedTabViewItems containsObject:clickedItem]) {
+            [_multiSelectedTabViewItems removeObject:clickedItem];
+            cell.isMultiSelected = NO;
+        } else {
+            [_multiSelectedTabViewItems addObject:clickedItem];
+            cell.isMultiSelected = YES;
+        }
+        [self _updateGroupSelectionButton];
+        return;
+    }
+
+    [self clearMultiSelection];
     if ([sender representedObject]) {
         [_tabView selectTabViewItem:[sender representedObject]];
         [self update];
@@ -2274,6 +2713,13 @@ - (void)tabClick:(id)sender {
 }
 
 - (void)tabDoubleClick:(id)sender {
+    NSTabViewItem *clickedItem = [sender representedObject];
+    if ([[clickedItem identifier] isKindOfClass:[iTermTabGroup class]]) {
+        if ([[self delegate] respondsToSelector:@selector(tabView:doubleClickGroupHeaderTabViewItem:)]) {
+            [[self delegate] tabView:_tabView doubleClickGroupHeaderTabViewItem:clickedItem];
+        }
+        return;
+    }
     if ([[self delegate] respondsToSelector:@selector(tabView:doubleClickTabViewItem:)]) {
         [[self delegate] tabView:[self tabView] doubleClickTabViewItem:[sender representedObject]];
     }
@@ -2498,6 +2944,9 @@ - (void)tabView:(NSTabView *)tabView doubleClickTabViewItem:(NSTabViewItem *)tab
 }
 
 - (BOOL)tabView:(NSTabView *)aTabView shouldSelectTabViewItem:(NSTabViewItem *)tabViewItem {
+    if ([[tabViewItem identifier] isKindOfClass:[iTermTabGroup class]]) {
+        return NO;
+    }
     if ([[self delegate] respondsToSelector:@selector(tabView:shouldSelectTabViewItem:)]) {
         return (BOOL)[[self delegate] tabView:aTabView shouldSelectTabViewItem:tabViewItem];
     } else {
@@ -2566,8 +3015,12 @@ - (NSString *)view:(NSView *)view stringForToolTip:(NSToolTipTag)tag point:(NSPo
         [self updateTooltipAppearance];
     });
 
+    PSMTabBarCell *cell = [self cellForPoint:point cellFrame:nil];
+    if (cell.isGroupHeader) {
+        return @"";
+    }
     if ([[self delegate] respondsToSelector:@selector(tabView:toolTipForTabViewItem:)]) {
-        return [[self delegate] tabView:[self tabView] toolTipForTabViewItem:[[self cellForPoint:point cellFrame:nil] representedObject]];
+        return [[self delegate] tabView:[self tabView] toolTipForTabViewItem:[cell representedObject]];
     }
     return @"";
 }
diff --git a/ThirdParty/PSMTabBarControl/source/PSMTahoeTabStyle.swift b/ThirdParty/PSMTabBarControl/source/PSMTahoeTabStyle.swift
index 168a28f844..a502a1848d 100644
--- a/ThirdParty/PSMTabBarControl/source/PSMTahoeTabStyle.swift
+++ b/ThirdParty/PSMTabBarControl/source/PSMTahoeTabStyle.swift
@@ -229,7 +229,7 @@ class PSMTahoeTabStyle: NSObject, PSMTabStyle {
     }
     
     @objc func closeButtonRect(forTabCell cell: PSMTabBarCell) -> NSRect {
-        if cell.isPinned {
+        if cell.isPinned || cell.isGroupHeader {
             return NSZeroRect
         }
         let cellFrame = cell.frame
@@ -317,6 +317,17 @@ class PSMTahoeTabStyle: NSObject, PSMTabStyle {
         if cell.isPinned {
             return Float(tabBar?.pinnedTabWidth ?? 0)
         }
+        if cell.isGroupHeader {
+            guard let displayName = groupHeaderDisplayName(for: cell) else {
+                return 40.0
+            }
+            let nameAttributes: [NSAttributedString.Key: Any] = [
+                .font: NSFont.systemFont(ofSize: fontSize, weight: .semibold)
+            ]
+            let nameWidth = ceil(displayName.size(withAttributes: nameAttributes).width)
+            let horizontalPadding = 52.0
+            return Float(ceil(nameWidth + horizontalPadding))
+        }
         return Float(ceil(widthOfLeftMatterInCell(cell) +
                           widthOfAttributedStringInCell(cell) +
                           widthOfRightMatterInCell(cell)))
@@ -488,10 +499,13 @@ class PSMTahoeTabStyle: NSObject, PSMTabStyle {
     }
     
     @objc func drawTabCell(_ cell: PSMTabBarCell, highlightAmount: CGFloat) {
+        if cell.isAnimatingCollapse {
+            return
+        }
         let horizontal = (_orientation == .horizontalOrientation)
         let isFirst = (cell == tabBar?.cells().firstObject as? PSMTabBarCell)
         let isLast = (cell == tabBar?.cells().lastObject as? PSMTabBarCell)
-        
+
         if tabBar?.window?.isKeyWindow == true {
             if cell.state == .on {
                 drawDropShadow(cell: cell)
@@ -504,15 +518,123 @@ class PSMTahoeTabStyle: NSObject, PSMTabStyle {
             withTabColor: cell.tabColor,
             isFirst: isFirst,
             isLast: isLast,
-            highlightAmount: highlightAmount,
+            highlightAmount: cell.isGroupHeader ? 0.0 : highlightAmount,
             isHighlighted: cell.isHighlighted)
-        drawInterior(with: cell, inView: cell.controlView, highlightAmount: highlightAmount)
-        
+        if cell.isGroupHeader, cell.groupColor != nil {
+            drawGroupHeaderDecorations(cell)
+        } else {
+            if cell.isGroupMember, cell.groupColor != nil {
+                drawGroupMemberDecoration(cell)
+            }
+            drawInterior(with: cell, inView: cell.controlView, highlightAmount: highlightAmount)
+        }
+
         if PSMTahoeTabStyleDebuggingEnabled {
             NSColor.red.set()
             cell.frame.frame(withWidth: 0.5)
         }
     }
+
+    private func drawGroupHeaderDecorations(_ cell: PSMTabBarCell) {
+        guard let groupColor = cell.groupColor else {
+            return
+        }
+        let cellFrame = cell.frame
+        let effectiveHighlight = max(cell.highlightAmount, cell.isGroupActive ? 0.5 : 0.0)
+
+        guard let displayName = groupHeaderDisplayName(for: cell) else {
+            let dotDiameter = 16.0
+            let dotRect = NSRect(x: cellFrame.midX - dotDiameter / 2.0,
+                                 y: cellFrame.midY - dotDiameter / 2.0,
+                                 width: dotDiameter,
+                                 height: dotDiameter)
+            if effectiveHighlight > 0.001 {
+                let haloDiameter = dotDiameter + 8.0
+                let haloRect = NSRect(x: cellFrame.midX - haloDiameter / 2.0,
+                                      y: cellFrame.midY - haloDiameter / 2.0,
+                                      width: haloDiameter,
+                                      height: haloDiameter)
+                groupColor.withAlphaComponent(effectiveHighlight * 0.3).set()
+                NSBezierPath(ovalIn: haloRect).fill()
+            }
+            groupColor.set()
+            NSBezierPath(ovalIn: dotRect).fill()
+            return
+        }
+
+        let horizontalMargin = 6.0
+        let verticalMargin = 4.0
+        var pillRect = backgroundRect(for: cellFrame).insetBy(dx: horizontalMargin, dy: verticalMargin)
+        if _orientation == .verticalOrientation {
+            // Vertical cells span the full bar width; hug the name instead of stretching.
+            let nameAttributes: [NSAttributedString.Key: Any] = [
+                .font: NSFont.systemFont(ofSize: fontSize, weight: .semibold)
+            ]
+            let nameWidth = ceil(displayName.size(withAttributes: nameAttributes).width)
+            let pillWidth = min(pillRect.width, nameWidth + horizontalMargin * 5)
+            pillRect = NSRect(x: cellFrame.midX - pillWidth / 2.0,
+                              y: pillRect.minY,
+                              width: pillWidth,
+                              height: pillRect.height)
+        }
+        let cornerRadius = pillRect.height / 2.0
+        let pill = NSBezierPath(roundedRect: pillRect, xRadius: cornerRadius, yRadius: cornerRadius)
+
+        var red: CGFloat = 0
+        var green: CGFloat = 0
+        var blue: CGFloat = 0
+        var alpha: CGFloat = 0
+        (groupColor.usingColorSpace(.sRGB) ?? groupColor).getRed(&red, green: &green, blue: &blue, alpha: &alpha)
+        let lightGroupColor = (0.299 * red + 0.587 * green + 0.114 * blue) > 0.55
+
+        groupColor.set()
+        pill.fill()
+
+        // Active state (a member tab is currently selected): persistent inner border
+        if cell.isGroupActive {
+            NSColor(white: lightGroupColor ? 0.0 : 1.0, alpha: 0.4).set()
+            pill.lineWidth = 1.5
+            pill.stroke()
+        }
+
+        // Hover: contrasting overlay that fades in with mouse position
+        if cell.highlightAmount > 0.001 {
+            NSColor(white: lightGroupColor ? 0.0 : 1.0, alpha: cell.highlightAmount * 0.25).set()
+            pill.fill()
+        }
+
+        let textColor = lightGroupColor ? NSColor(white: 0.1, alpha: 1.0) : .white
+        let nameAttributes: [NSAttributedString.Key: Any] = [
+            .font: NSFont.systemFont(ofSize: fontSize, weight: .semibold),
+            .foregroundColor: textColor
+        ]
+        let nameSize = displayName.size(withAttributes: nameAttributes)
+        displayName.draw(at: NSPoint(x: pillRect.midX - nameSize.width / 2.0,
+                                   y: pillRect.midY - nameSize.height / 2.0),
+                       withAttributes: nameAttributes)
+    }
+
+    private func drawGroupMemberDecoration(_ cell: PSMTabBarCell) {
+        guard let groupColor = cell.groupColor else {
+            return
+        }
+        let radius = max(0, barRadius - 2.5)
+        let rect = backgroundRect(for: cell.frame)
+        if cell.state == .on {
+            // Selected member: thin group-colour ring around the regular pill.
+            let ring = NSBezierPath(roundedRect: rect.insetBy(dx: 0.75, dy: 0.75),
+                                    xRadius: max(0, radius - 0.75),
+                                    yRadius: max(0, radius - 0.75))
+            groupColor.set()
+            ring.lineWidth = 1.5
+            ring.stroke()
+        } else {
+            // Unselected member: subtle wash of the group colour across the pill.
+            let pill = NSBezierPath(roundedRect: rect, xRadius: radius, yRadius: radius)
+            groupColor.withAlphaComponent(0.14).set()
+            pill.fill()
+        }
+    }
     
     private func drawDropShadow(cell: PSMTabBarCell) {
         let scale = cell.controlView?.window?.backingScaleFactor ?? 2.0
@@ -664,6 +786,9 @@ class PSMTahoeTabStyle: NSObject, PSMTabStyle {
                 let cell = drawableCells.remove(at: i)
                 drawableCells.append(cell)
             }
+            // Soft group wash sits behind the tabs so it never competes with the
+            // per-tab loading bar (which owns the top edge).
+            drawGroupContainerFills(bar: bar)
             for cell in drawableCells {
                 cell.draw(withFrame: cell.frame, in: bar)
             }
@@ -685,12 +810,76 @@ class PSMTahoeTabStyle: NSObject, PSMTabStyle {
             for i in 0..<(sorted.count - 1) {
                 drawDivider(betweenCell: sorted[i], andCell: sorted[i + 1])
             }
+            drawGroupContainerBorders(bar: bar)
             if let selectedCell = drawableCells.first, selectedCell.state == .on {
                 selectedCell.drawPostHocDecorations(onSelectedCell: selectedCell, tabBarControl: bar)
             }
         }
     }
 
+    // A group reads as a Chrome-style tinted container — a region, not a line —
+    // so it can never be confused with or collide against the per-tab loading
+    // bar. Each contiguous run of (header + its member cells) yields one rounded
+    // container: a soft fill drawn behind the tabs and a crisp outline over them.
+    private func groupRuns(bar: PSMTabBarControl) -> [(rect: NSRect, color: NSColor)] {
+        guard _orientation == .horizontalOrientation,
+              let cells = bar.cells() as? [PSMTabBarCell] else {
+            return []
+        }
+        var runs: [(rect: NSRect, color: NSColor)] = []
+        var i = 0
+        while i < cells.count {
+            let header = cells[i]
+            guard header.isGroupHeader, let groupColor = header.groupColor, !header.isInOverflowMenu else {
+                i += 1
+                continue
+            }
+            var runRect = header.frame
+            var j = i + 1
+            while j < cells.count {
+                let member = cells[j]
+                if !member.isGroupMember || member.isInOverflowMenu || member.groupColor != groupColor {
+                    break
+                }
+                runRect = runRect.union(member.frame)
+                j += 1
+            }
+            runs.append((runRect, groupColor))
+            i = j
+        }
+        return runs
+    }
+
+    private func groupContainerPath(for runRect: NSRect) -> NSBezierPath {
+        let containerRect = runRect.insetBy(dx: 2, dy: 3)
+        let radius = 6.0
+        return NSBezierPath(roundedRect: containerRect, xRadius: radius, yRadius: radius)
+    }
+
+    private func drawGroupContainerFills(bar: PSMTabBarControl) {
+        for run in groupRuns(bar: bar) {
+            run.color.withAlphaComponent(0.15).setFill()
+            groupContainerPath(for: run.rect).fill()
+        }
+    }
+
+    private func drawGroupContainerBorders(bar: PSMTabBarControl) {
+        for run in groupRuns(bar: bar) {
+            let path = groupContainerPath(for: run.rect)
+            path.lineWidth = 1.0
+            run.color.withAlphaComponent(0.55).setStroke()
+            path.stroke()
+        }
+    }
+
+    private func groupHeaderDisplayName(for cell: PSMTabBarCell) -> String? {
+        let name = cell.groupName ?? ""
+        if cell.isGroupCollapsed, cell.groupMemberCount > 0 {
+            return name.isEmpty ? "\(cell.groupMemberCount)" : "\(name) (\(cell.groupMemberCount))"
+        }
+        return name.isEmpty ? nil : name
+    }
+
     var dividerColor: NSColor {
         NSColor(displayP3Red: 0.82, green: 0.82, blue: 0.82, alpha: 1.0)
     }
diff --git a/ThirdParty/PSMTabBarControl/source/PSMYosemiteTabStyle.m b/ThirdParty/PSMTabBarControl/source/PSMYosemiteTabStyle.m
index 9796841e44..447a9346b7 100644
--- a/ThirdParty/PSMTabBarControl/source/PSMYosemiteTabStyle.m
+++ b/ThirdParty/PSMTabBarControl/source/PSMYosemiteTabStyle.m
@@ -183,7 +183,7 @@ - (NSRect)dragRectForTabCell:(PSMTabBarCell *)cell
 }
 
 - (NSRect)closeButtonRectForTabCell:(PSMTabBarCell *)cell {
-    if (cell.isPinned) {
+    if (cell.isPinned || cell.isGroupHeader) {
         return NSZeroRect;
     }
     NSRect cellFrame = [cell frame];
@@ -424,6 +424,16 @@ - (float)desiredWidthOfTabCell:(PSMTabBarCell *)cell {
     if (cell.isPinned) {
         return self.tabBar.pinnedTabWidth;
     }
+    if (cell.isGroupHeader) {
+        NSString *displayName = [self groupHeaderDisplayNameForCell:cell];
+        if (!displayName.length) {
+            return 40.0;
+        }
+        NSDictionary *nameAttrs = @{ NSFontAttributeName: [NSFont systemFontOfSize:self.fontSize weight:NSFontWeightSemibold] };
+        CGFloat nameWidth = ceil([displayName sizeWithAttributes:nameAttrs].width);
+        const CGFloat hPad = 52.0;
+        return ceil(nameWidth + hPad);
+    }
     return ceil([self widthOfLeftMatterInCell:cell] +
                 [self widthOfAttributedStringInCell:cell] +
                 [self widthOfRightMatterInCell:cell]);
@@ -519,7 +529,7 @@ - (PSMCachedTitleInputs *)cachedTitleInputsForTabCell:(PSMTabBarCell *)cell {
     PSMCachedTitleInputs *inputs = [[PSMCachedTitleInputs alloc] initWithTitle:title
                                                                truncationStyle:cell.truncationStyle
                                                                          color:[self textColorForCell:cell]
-                                                                       graphic:[(id)[[cell representedObject] identifier] psmTabGraphic]
+                                                                       graphic:cell.isGroupHeader ? nil : [(id)[[cell representedObject] identifier] psmTabGraphic]
                                                                    orientation:_orientation
                                                                       fontSize:self.fontSize
                                                                      parseHTML:parseHTML
@@ -802,6 +812,9 @@ - (NSEdgeInsets)insetsForTabBarDividers {
 }
 
 - (void)drawTabCell:(PSMTabBarCell *)cell highlightAmount:(CGFloat)highlightAmount {
+    if (cell.isAnimatingCollapse) {
+        return;
+    }
     // TODO: Test hidden control, whose height is less than 2. Maybe it happens while dragging?
     [self drawCellBackgroundAndFrameHorizontallyOriented:(_orientation == PSMTabBarHorizontalOrientation)
                                                   inRect:cell.frame
@@ -809,8 +822,121 @@ - (void)drawTabCell:(PSMTabBarCell *)cell highlightAmount:(CGFloat)highlightAmou
                                             withTabColor:[cell tabColor]
                                                  isFirst:cell == _tabBar.cells.firstObject
                                                   isLast:cell == _tabBar.cells.lastObject
-                                         highlightAmount:highlightAmount];
-    [self drawInteriorWithTabCell:cell inView:[cell controlView] highlightAmount:highlightAmount];
+                                         highlightAmount:cell.isGroupHeader ? 0.0 : highlightAmount];
+    if (cell.isGroupHeader && cell.groupColor) {
+        [self drawGroupHeaderDecorations:cell];
+    } else {
+        if (cell.isGroupMember && cell.groupColor) {
+            [self drawGroupMemberDecoration:cell];
+        }
+        [self drawInteriorWithTabCell:cell inView:[cell controlView] highlightAmount:highlightAmount];
+    }
+}
+
+- (NSString *)groupHeaderDisplayNameForCell:(PSMTabBarCell *)cell {
+    if (cell.isGroupCollapsed && cell.groupMemberCount > 0) {
+        if (cell.groupName.length) {
+            return [NSString stringWithFormat:@"%@ (%@)", cell.groupName, @(cell.groupMemberCount)];
+        }
+        return [@(cell.groupMemberCount) stringValue];
+    }
+    return cell.groupName ?: @"";
+}
+
+- (void)drawGroupHeaderDecorations:(PSMTabBarCell *)cell {
+    NSRect cellFrame = cell.frame;
+    NSString *displayName = [self groupHeaderDisplayNameForCell:cell];
+    BOOL hasName = displayName.length > 0;
+    const CGFloat effectiveHighlight = MAX(cell.highlightAmount, cell.isGroupActive ? 0.5 : 0.0);
+
+    const CGFloat hMargin = 10.0;
+    const CGFloat vMargin = 5.0;
+    const CGFloat cornerRadius = 4.0;
+
+    NSColor *srgb = [cell.groupColor colorUsingColorSpace:NSColorSpace.sRGBColorSpace];
+    CGFloat r, g, b, a;
+    [srgb getRed:&r green:&g blue:&b alpha:&a];
+    const BOOL lightGroupColor = (0.299 * r + 0.587 * g + 0.114 * b) > 0.55;
+
+    if (!hasName) {
+        const CGFloat dotDiameter = 16.0;
+        NSRect dotRect = NSMakeRect(NSMidX(cellFrame) - dotDiameter / 2.0,
+                                    NSMidY(cellFrame) - dotDiameter / 2.0,
+                                    dotDiameter, dotDiameter);
+        if (effectiveHighlight > 0.001) {
+            const CGFloat haloDiameter = dotDiameter + 8.0;
+            NSRect haloRect = NSMakeRect(NSMidX(cellFrame) - haloDiameter / 2.0,
+                                         NSMidY(cellFrame) - haloDiameter / 2.0,
+                                         haloDiameter, haloDiameter);
+            [[cell.groupColor colorWithAlphaComponent:effectiveHighlight * 0.3] set];
+            [[NSBezierPath bezierPathWithOvalInRect:haloRect] fill];
+        }
+        [cell.groupColor set];
+        [[NSBezierPath bezierPathWithOvalInRect:dotRect] fill];
+        return;
+    }
+
+    NSRect pillRect = NSMakeRect(cellFrame.origin.x + hMargin,
+                                 cellFrame.origin.y + vMargin,
+                                 cellFrame.size.width - hMargin * 2,
+                                 cellFrame.size.height - vMargin * 2);
+    if (_orientation == PSMTabBarVerticalOrientation) {
+        // Vertical cells span the full bar width; hug the name instead of stretching.
+        NSDictionary *measureAttrs = @{ NSFontAttributeName: [NSFont systemFontOfSize:self.fontSize
+                                                                                weight:NSFontWeightSemibold] };
+        const CGFloat nameWidth = ceil([displayName sizeWithAttributes:measureAttrs].width);
+        const CGFloat pillWidth = MIN(NSWidth(pillRect), nameWidth + hMargin * 3);
+        pillRect = NSMakeRect(NSMidX(cellFrame) - pillWidth / 2.0,
+                              pillRect.origin.y,
+                              pillWidth,
+                              pillRect.size.height);
+    }
+    NSBezierPath *outerPill = [NSBezierPath bezierPathWithRoundedRect:pillRect
+                                                             xRadius:cornerRadius
+                                                             yRadius:cornerRadius];
+
+    [cell.groupColor set];
+    [outerPill fill];
+
+    // Active state (a member tab is currently selected): persistent inner border
+    if (cell.isGroupActive) {
+        [[NSColor colorWithWhite:lightGroupColor ? 0.0 : 1.0 alpha:0.4] set];
+        [outerPill setLineWidth:1.5];
+        [outerPill stroke];
+    }
+
+    // Hover: contrasting overlay that fades in with mouse position
+    if (cell.highlightAmount > 0.001) {
+        [[NSColor colorWithWhite:lightGroupColor ? 0.0 : 1.0 alpha:cell.highlightAmount * 0.25] set];
+        [outerPill fill];
+    }
+
+    NSColor *textColor = lightGroupColor ? [NSColor colorWithWhite:0.1 alpha:1.0]
+                                         : [NSColor whiteColor];
+
+    NSDictionary *nameAttrs = @{
+        NSFontAttributeName: [NSFont systemFontOfSize:self.fontSize weight:NSFontWeightSemibold],
+        NSForegroundColorAttributeName: textColor
+    };
+    NSSize nameSize = [displayName sizeWithAttributes:nameAttrs];
+    [displayName drawAtPoint:NSMakePoint(NSMidX(pillRect) - nameSize.width / 2.0,
+                                         NSMidY(pillRect) - nameSize.height / 2.0)
+                 withAttributes:nameAttrs];
+}
+
+- (void)drawGroupMemberDecoration:(PSMTabBarCell *)cell {
+    NSRect cellFrame = cell.frame;
+    if (cell.state == NSControlStateValueOn) {
+        // Selected member: thin group-colour inner border around the tab.
+        NSBezierPath *ring = [NSBezierPath bezierPathWithRect:NSInsetRect(cellFrame, 1.0, 1.0)];
+        [cell.groupColor set];
+        [ring setLineWidth:1.5];
+        [ring stroke];
+    } else {
+        // Unselected member: subtle wash of the group colour across the tab.
+        [[cell.groupColor colorWithAlphaComponent:0.14] set];
+        NSRectFillUsingOperation(cellFrame, NSCompositingOperationSourceOver);
+    }
 }
 
 - (CGFloat)tabColorBrightness:(PSMTabBarCell *)cell {
@@ -1325,10 +1451,20 @@ - (void)drawTabBar:(PSMTabBarControl *)bar
         for (PSMTabBarCell *cell in [bar cells]) {
             if (![cell isInOverflowMenu] && NSIntersectsRect(NSInsetRect([cell frame], -1, -1), clipRect)) {
                 if (cell.state == stateToDraw) {
-                    [cell drawWithFrame:[cell frame] inView:bar];
+                    CGContextRef ctx = [NSGraphicsContext currentContext].CGContext;
+                    const NSRect drawFrame = cell.frame;
+                    [cell drawWithFrame:drawFrame inView:bar];
                     if ([self shouldDrawTopLineSelected:(stateToDraw == NSControlStateValueOn) attached:attachedToTitleBar position:bar.tabLocation]) {
                         [topLineColor set];
-                        NSRectFill(NSMakeRect(NSMinX(cell.frame), 0, NSWidth(cell.frame), 1));
+                        NSRectFill(NSMakeRect(NSMinX(drawFrame), 0, NSWidth(drawFrame), 1));
+                    }
+                    if (cell.isMultiSelected) {
+                        CGContextSaveGState(ctx);
+                        [[NSColor colorWithWhite:1.0 alpha:0.08] setFill];
+                        NSRectFillUsingOperation(drawFrame, NSCompositingOperationSourceOver);
+                        [[NSColor colorWithWhite:1.0 alpha:0.25] setFill];
+                        NSRectFillUsingOperation(NSMakeRect(NSMinX(drawFrame), NSMaxY(drawFrame) - 1.0, NSWidth(drawFrame), 1.0), NSCompositingOperationSourceOver);
+                        CGContextRestoreGState(ctx);
                     }
                     if (stateToDraw == NSControlStateValueOn) {
                         // Can quit early since only one can be selected
@@ -1357,6 +1493,7 @@ - (void)drawTabBar:(PSMTabBarControl *)bar
     }
 }
 
+
 - (void)drawDividerBetweenTabBarAndContent:(NSRect)rect bar:(PSMTabBarControl *)bar {
     if (_orientation != PSMTabBarHorizontalOrientation) {
         [[self bottomLineColorSelected:NO] set];
diff --git a/docs/notes-3.7.txt b/docs/notes-3.7.txt
index 87d7fe550e..9ef4f732e2 100644
--- a/docs/notes-3.7.txt
+++ b/docs/notes-3.7.txt
@@ -9,6 +9,15 @@ to version 3.6.7 and duplicates some items in
 betas since then.
 
 Major New Features:
+- Tabs can now be organized into groups. Select
+  multiple tabs with cmd-click and click the
+  Group button to create a named, color-coded
+  group. Group headers appear in the tab bar;
+  click one to collapse or expand its tabs.
+  Drag a tab into or out of a group to change
+  its membership. Groups are saved in window
+  arrangements.
+
 - In the Jobs view (toolbelt and status bar
   popover) hovering a row shows the full
   command as a tooltip, and pressing space
diff --git a/iTerm2.xcodeproj/project.pbxproj b/iTerm2.xcodeproj/project.pbxproj
index 8974e39c55..1f6371b8af 100644
--- a/iTerm2.xcodeproj/project.pbxproj
+++ b/iTerm2.xcodeproj/project.pbxproj
@@ -961,6 +961,7 @@
 		6A8ED0F641A9897F39D60FBE /* VT100ScreenState+RCDataSource.m in Sources */ = {isa = PBXBuildFile; fileRef = DB46A60B018E4C5F6859B164 /* VT100ScreenState+RCDataSource.m */; };
 		6C0FD6BA115D3C08BBE009B0 /* iTermImageComparison.m in Sources */ = {isa = PBXBuildFile; fileRef = 2AEB275FE345E8480B41FAEF /* iTermImageComparison.m */; };
 		6C1249B29C2376A669BE56BE /* iTermLayoutSpecValidator.swift in Sources */ = {isa = PBXBuildFile; fileRef = E6BC074C860759EEDF3F98F0 /* iTermLayoutSpecValidator.swift */; };
+		6C24405FAEB62E4BB0019A8B /* iTermTabGroup.swift in Sources */ = {isa = PBXBuildFile; fileRef = B51E1F6235B4C132F26BE5A5 /* iTermTabGroup.swift */; };
 		6CE3AED77D074C569A3D6D07 /* iTermOpenDirectory.m in Sources */ = {isa = PBXBuildFile; fileRef = 53A96ECF2322040C00AEA8E0 /* iTermOpenDirectory.m */; };
 		6DE326D917E8D3D7A0A037B8 /* WorkgroupChildSpawning.swift in Sources */ = {isa = PBXBuildFile; fileRef = A25EF27A7558A60A0553EDC9 /* WorkgroupChildSpawning.swift */; };
 		70F805A3A750CCB540F58C9A /* MovePaneController+API.swift in Sources */ = {isa = PBXBuildFile; fileRef = 40D246CFCEDD7927D320BF51 /* MovePaneController+API.swift */; };
@@ -5353,6 +5354,7 @@
 		B2CA85E23B4CCCC3391BA025 /* NotifyingDictionary.swift in Sources */ = {isa = PBXBuildFile; fileRef = 877B9444B69DE32D9CF87354 /* NotifyingDictionary.swift */; };
 		B3E079E1F626A259EDC76153 /* PeerSessionSettingsViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 3298E60BA3D410B4C3FC1A98 /* PeerSessionSettingsViewController.swift */; };
 		B3F134FF5266734ED326399E /* AICustomHeaders.swift in Sources */ = {isa = PBXBuildFile; fileRef = 3E6892F33EA732E982A1991D /* AICustomHeaders.swift */; };
+		B5251D317DB4504A2E795AD4 /* iTermCreateTabGroupViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 2612CE8B4B477ADE822DF001 /* iTermCreateTabGroupViewController.swift */; };
 		B89533C4F0E3E8C415065AAC /* iTermLayoutResolver.swift in Sources */ = {isa = PBXBuildFile; fileRef = D079EA4C9132883E833B9974 /* iTermLayoutResolver.swift */; };
 		B947C485FA069D07B72E94CC /* iTermWorkgroupToolbarItem.swift in Sources */ = {isa = PBXBuildFile; fileRef = A07263500827075018158DEC /* iTermWorkgroupToolbarItem.swift */; };
 		B9B050C66BE98825D6AFEE47 /* cloak-page-world.js in Resources */ = {isa = PBXBuildFile; fileRef = ED1DEABF73F84ABCF9B2FDC8 /* cloak-page-world.js */; };
@@ -5375,6 +5377,7 @@
 		C7085CEC5C90392327148ECF /* VT100ScreenState+RCDataSource.h in Sources */ = {isa = PBXBuildFile; fileRef = 581A5EEA45904BD841D277FA /* VT100ScreenState+RCDataSource.h */; };
 		C74DEE2C4422D9EDBB63D33C /* WorkgroupSessionSpawner.swift in Sources */ = {isa = PBXBuildFile; fileRef = B21F806A265725167FCCDFC1 /* WorkgroupSessionSpawner.swift */; };
 		C7A0BDF06AF4B83133A0C70C /* WorkgroupAnimalNames.swift in Sources */ = {isa = PBXBuildFile; fileRef = 67233FA25C3C82AA22B62E01 /* WorkgroupAnimalNames.swift */; };
+		CABB49C0B6774623FB175D60 /* PseudoTerminal+TabGroups.swift in Sources */ = {isa = PBXBuildFile; fileRef = 64C66C696B4432394394E845 /* PseudoTerminal+TabGroups.swift */; };
 		CC1EDD90C29B2AFC43831C81 /* VT100StringConversionConfig.h in Sources */ = {isa = PBXBuildFile; fileRef = 6F87CB3CBFBF0D0E8781513C /* VT100StringConversionConfig.h */; };
 		CD2E8590B507B08EBD3313A3 /* iTermCompactProxyIconView.swift in Sources */ = {isa = PBXBuildFile; fileRef = E6CB27B6647329ACD05CE222 /* iTermCompactProxyIconView.swift */; };
 		CF138846630690AA6A7BCFD5 /* iTermGitClient.m in Sources */ = {isa = PBXBuildFile; fileRef = A687B66925AD6FF600E0A658 /* iTermGitClient.m */; };
@@ -6220,6 +6223,7 @@
 		234916CDB04523CFD1E0390B /* ClippingsView.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = ClippingsView.swift; sourceTree = "<group>"; };
 		23DA26C236E4BC3ECF3CF916 /* WorkgroupModeSwitcherItem.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = WorkgroupModeSwitcherItem.swift; sourceTree = "<group>"; };
 		240C63271364D969B638DA6E /* ResilientCoordinateNotifications.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = ResilientCoordinateNotifications.swift; sourceTree = "<group>"; };
+		2612CE8B4B477ADE822DF001 /* iTermCreateTabGroupViewController.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = iTermCreateTabGroupViewController.swift; sourceTree = "<group>"; };
 		26D937108B4A3A7BC121FF1D /* iTermWorkgroupToolbarItemRegistry.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = iTermWorkgroupToolbarItemRegistry.swift; sourceTree = "<group>"; };
 		28AF992AB875E6786421227B /* iTermScreenshotOnDemandPreview.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = iTermScreenshotOnDemandPreview.swift; sourceTree = "<group>"; };
 		2AEB275FE345E8480B41FAEF /* iTermImageComparison.m */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.c.objc; path = iTermImageComparison.m; sourceTree = "<group>"; };
@@ -6495,6 +6499,7 @@
 		61DE2C181D86B1F93619B375 /* iTermSessionNameBuiltInFunction.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = iTermSessionNameBuiltInFunction.swift; sourceTree = "<group>"; };
 		625C956DD832F4FD0D8F9715 /* PrivateIPChecker.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = PrivateIPChecker.swift; sourceTree = "<group>"; };
 		6373295DEB74E8DFC995A362 /* iTermAdapterSettingsRevealHelper.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = iTermAdapterSettingsRevealHelper.swift; sourceTree = "<group>"; };
+		64C66C696B4432394394E845 /* PseudoTerminal+TabGroups.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = "PseudoTerminal+TabGroups.swift"; sourceTree = "<group>"; };
 		64D77A978A9DB0DB1AC8DE61 /* AILiveChatQueueTests.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = AILiveChatQueueTests.swift; sourceTree = "<group>"; };
 		6518C4017AD4275634FA34AA /* iTermRightGutterPanelRegistry.h */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.c.h; path = iTermRightGutterPanelRegistry.h; sourceTree = "<group>"; };
 		67233FA25C3C82AA22B62E01 /* WorkgroupAnimalNames.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = WorkgroupAnimalNames.swift; sourceTree = "<group>"; };
@@ -9536,6 +9541,7 @@
 		B231EDB860248C368A511B42 /* iTermEventTriggerEvaluator.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = iTermEventTriggerEvaluator.swift; sourceTree = "<group>"; };
 		B23866DFB3D15427C93C0849 /* EnterWorkgroupTrigger.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = EnterWorkgroupTrigger.swift; sourceTree = "<group>"; };
 		B391267E5EE9115AFB3E94B1 /* AISafetyClassifierBackend.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = AISafetyClassifierBackend.swift; sourceTree = "<group>"; };
+		B51E1F6235B4C132F26BE5A5 /* iTermTabGroup.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = iTermTabGroup.swift; sourceTree = "<group>"; };
 		B5E07413F98A022F224813BE /* AILiveDriver.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = AILiveDriver.swift; sourceTree = "<group>"; };
 		B673BD86C08D1241D0DDA4C1 /* ExitWorkgroupBrowserTrigger.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = ExitWorkgroupBrowserTrigger.swift; sourceTree = "<group>"; };
 		B73FCEC5593D29C35827971E /* ClaudeCodeModeController.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = ClaudeCodeModeController.swift; sourceTree = "<group>"; };
@@ -13888,6 +13894,9 @@
 				89D3137ADD4526A5A2012D83 /* iTermLayoutMutator.swift */,
 				77FCEB05FACE33F5F7947261 /* iTermWindowBorderView.swift */,
 				F98ADE6D889E9911953ECB78 /* iTermGutterPanelWidths.swift */,
+				B51E1F6235B4C132F26BE5A5 /* iTermTabGroup.swift */,
+				64C66C696B4432394394E845 /* PseudoTerminal+TabGroups.swift */,
+				2612CE8B4B477ADE822DF001 /* iTermCreateTabGroupViewController.swift */,
 			);
 			path = TerminalView;
 			sourceTree = "<group>";
@@ -21519,6 +21528,9 @@
 				9A0CA7F82D9DB1934FC5BB8C /* ChatMentionPickerController.swift in Sources */,
 				096EE94A89ADAAA4B4A2ACF9 /* ChatIconGenerator.swift in Sources */,
 				815BF5D942C3EAAF56D7E2A7 /* AIPromptTemplateEvaluator.swift in Sources */,
+				6C24405FAEB62E4BB0019A8B /* iTermTabGroup.swift in Sources */,
+				CABB49C0B6774623FB175D60 /* PseudoTerminal+TabGroups.swift in Sources */,
+				B5251D317DB4504A2E795AD4 /* iTermCreateTabGroupViewController.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
diff --git a/sources/AppKit/iTermApplicationDelegate.m b/sources/AppKit/iTermApplicationDelegate.m
index a787b34d09..d6740aeb99 100644
--- a/sources/AppKit/iTermApplicationDelegate.m
+++ b/sources/AppKit/iTermApplicationDelegate.m
@@ -2502,7 +2502,8 @@ - (void)buildSessionSubmenu:(NSNotification *)aNotification {
     }
 
     for (NSTabViewItem *aTabViewItem in tabViewItemArray) {
-        PTYTab *aTab = [aTabViewItem identifier];
+        PTYTab *aTab = aTabViewItem.it_tab;
+        if (!aTab) { continue; }
         NSMenuItem *aMenuItem;
 
         if ([aTab activeSession]) {
diff --git a/sources/TerminalView/PTYTab.h b/sources/TerminalView/PTYTab.h
index 8143b8bf0f..cdedc66996 100644
--- a/sources/TerminalView/PTYTab.h
+++ b/sources/TerminalView/PTYTab.h
@@ -353,3 +353,9 @@ extern NSString *const PTYTabArrangementOptionsPendingJumps;
 - (void)didSelectTab;
 
 @end
+
+// Tab view items normally have a PTYTab identifier, but tab-group header items do not.
+@interface NSTabViewItem (iTermPTYTab)
+// The owning PTYTab, or nil if this item is a tab-group header rather than a real tab.
+@property (nonatomic, readonly) PTYTab *it_tab;
+@end
diff --git a/sources/TerminalView/PTYTab.m b/sources/TerminalView/PTYTab.m
index d39e6c4f06..9eaa8030c5 100644
--- a/sources/TerminalView/PTYTab.m
+++ b/sources/TerminalView/PTYTab.m
@@ -7583,3 +7583,15 @@ - (NSString *)stringUniqueIdentifier {
 }
 
 @end
+
+@implementation NSTabViewItem (iTermPTYTab)
+
+- (PTYTab *)it_tab {
+    id identifier = self.identifier;
+    if ([identifier isKindOfClass:[PTYTab class]]) {
+        return identifier;
+    }
+    return nil;
+}
+
+@end
diff --git a/sources/TerminalView/PseudoTerminal+Private.h b/sources/TerminalView/PseudoTerminal+Private.h
index 2b46cc8450..daaf8bc895 100644
--- a/sources/TerminalView/PseudoTerminal+Private.h
+++ b/sources/TerminalView/PseudoTerminal+Private.h
@@ -84,6 +84,7 @@ extern NSString *const TERMINAL_ARRANGEMENT_SIZE_LOCKED;
     NSArray *_screenConfigurationAtTimeOfForceFrame;
 
     BOOL _willClose;
+    BOOL _groupCollapseManaging;
 
     // DO NOT ACCESS DIRECTLY - USE ACCESSORS INSTEAD
     iTermWindowType _windowType;
@@ -122,9 +123,10 @@ extern NSString *const TERMINAL_ARRANGEMENT_SIZE_LOCKED;
 // Used to make restoring fullscreen windows work on 10.11.
 @property(nonatomic, copy) void (^didEnterLionFullscreen)(PseudoTerminal *);
 
-// This is a reference to the window's content view, here for convenience because it has
-// the right type.
-@property (nonatomic, readonly) __unsafe_unretained iTermRootTerminalView *contentView;
+@property (nonatomic, readonly) NSMutableArray *mutableTabGroups;
+@property (nonatomic, assign) BOOL groupCollapseManaging;
+@property (nonatomic, readonly) NSColor *minimalTabStyleBackgroundColor;
+@property (nonatomic, readonly) NSAppearance *sheetAppearance;
 
 - (void)returnTabBarToContentView;
 - (void)updateForTransparency:(NSWindow<PTYWindow> *)window;
diff --git a/sources/TerminalView/PseudoTerminal+TabGroups.swift b/sources/TerminalView/PseudoTerminal+TabGroups.swift
new file mode 100644
index 0000000000..5a4ead5f02
--- /dev/null
+++ b/sources/TerminalView/PseudoTerminal+TabGroups.swift
@@ -0,0 +1,564 @@
+import Cocoa
+
+private let iTermTabGroupsArrangementKey = "Tab Groups"
+
+extension PseudoTerminal {
+
+    @objc var tabGroups: [iTermTabGroup] {
+        return mutableTabGroups as! [iTermTabGroup]
+    }
+
+    @objc @discardableResult
+    func createTabGroup(name: String, color: NSColor, forTab tab: PTYTab) -> iTermTabGroup {
+        let group = iTermTabGroup(name: name, color: color)
+        mutableTabGroups.add(group)
+        insertHeaderItem(for: group, adjacentTo: tab)
+        addTab(tab, toGroup: group)
+        moveGroupAfterLastGroup(group)
+        autoManageGroupCollapseForTab(tab)
+        if let tabViewItem = tab.tabViewItem {
+            contentView.tabView.selectTabViewItem(tabViewItem)
+        }
+        return group
+    }
+
+    private func insertHeaderItem(for group: iTermTabGroup, adjacentTo tab: PTYTab) {
+        guard let tabItem = tab.tabViewItem else { return }
+        let tabView = contentView.tabView
+        let tabIndex = tabView.indexOfTabViewItem(tabItem)
+        if tabIndex != NSNotFound {
+            tabView.insertTabViewItem(group.headerTabViewItem, at: tabIndex)
+        } else {
+            tabView.insertTabViewItem(group.headerTabViewItem, at: tabView.numberOfTabViewItems)
+        }
+    }
+
+    private func moveGroupAfterLastGroup(_ group: iTermTabGroup) {
+        let tabView = contentView.tabView
+        let allTabs = tabs() ?? []
+
+        // Find the index just after the last tab that belongs to any other group.
+        var insertionIndex = 0
+        for i in 0..<tabView.numberOfTabViewItems {
+            let item = tabView.tabViewItem(at: i)
+            if item === group.headerTabViewItem { continue }
+            if let tab = item.identifier as? PTYTab, tab.isPinned {
+                insertionIndex = i + 1
+                continue
+            }
+            let belongsToOtherGroup = tabGroups.contains { g in
+                g !== group && (g.headerTabViewItem === item || g.memberTabIDs.contains { id in
+                    allTabs.first { Int($0.uniqueId) == id }?.tabViewItem === item
+                })
+            }
+            if belongsToOtherGroup {
+                insertionIndex = i + 1
+            }
+        }
+
+        let memberTabs = group.memberTabIDs.compactMap { id in allTabs.first { Int($0.uniqueId) == id } }
+        var itemsToMove: [NSTabViewItem] = [group.headerTabViewItem]
+        itemsToMove += memberTabs.compactMap { $0.tabViewItem }
+
+        for (offset, item) in itemsToMove.enumerated() {
+            let currentIndex = tabView.indexOfTabViewItem(item)
+            guard currentIndex != NSNotFound else { continue }
+            tabView.removeTabViewItem(item)
+            let target = min(insertionIndex + offset, tabView.numberOfTabViewItems)
+            tabView.insertTabViewItem(item, at: target)
+        }
+    }
+
+    @objc func addTab(_ tab: PTYTab, toGroup group: iTermTabGroup) {
+        let tabID = Int(tab.uniqueId)
+        guard !group.memberTabIDs.contains(tabID) else { return }
+        group.memberTabIDs.append(tabID)
+        if group.isCollapsed {
+            expandGroupSilently(group)
+        }
+        enforceContiguity(of: group)
+        updateTabGroupDecorations()
+    }
+
+    @objc func removeTab(_ tab: PTYTab, fromGroup group: iTermTabGroup) {
+        let tabID = Int(tab.uniqueId)
+        group.memberTabIDs.removeAll { $0 == tabID }
+        if group.isCollapsed {
+            group.stashedTabViewItems.removeAll { $0.identifier as? PTYTab === tab }
+        }
+        if group.memberTabIDs.isEmpty {
+            deleteTabGroup(group)
+        } else {
+            updateTabGroupDecorations()
+        }
+    }
+
+    @objc func deleteTabGroup(_ group: iTermTabGroup) {
+        if group.isCollapsed {
+            unstashItems(for: group)
+        }
+        contentView.tabView.removeTabViewItem(group.headerTabViewItem)
+        group.headerTabViewItem.identifier = nil
+        group.memberTabIDs.removeAll()
+        mutableTabGroups.remove(group)
+        updateTabGroupDecorations()
+    }
+
+    @objc func ungroupTabs(_ sender: Any?) {
+        guard let group = tabGroupFromSender(sender) else { return }
+        deleteTabGroup(group)
+    }
+
+    @objc func newTabInGroup(_ sender: Any?) {
+        guard let group = tabGroupFromSender(sender) else { return }
+        newTab(inGroup: group)
+    }
+
+    func newTab(inGroup group: iTermTabGroup) {
+        let profile = currentSession()?.profile ?? ProfileModel.sharedInstance().defaultProfile()
+        asyncCreateTab(withProfile: profile,
+                       withCommand: nil,
+                       environment: nil,
+                       tabIndex: nil,
+                       didMakeSession: nil) { [weak self] session, ok in
+            guard let self, ok, let tab = session?.delegate as? PTYTab else { return }
+            self.addTab(tab, toGroup: group)
+        }
+    }
+
+    @objc func closeTabGroup(_ sender: Any?) {
+        guard let group = tabGroupFromSender(sender) else { return }
+        closeGroup(group)
+    }
+
+    @objc func closeGroup(_ group: iTermTabGroup) {
+        if group.isCollapsed {
+            expandGroupSilently(group)
+        }
+        let allTabs = tabs() ?? []
+        let members = group.memberTabIDs.compactMap { id in allTabs.first { Int($0.uniqueId) == id } }
+        for tab in members {
+            close(tab)
+        }
+    }
+
+    @objc func toggleCollapseGroupFromMenu(_ sender: Any?) {
+        guard let group = tabGroupFromSender(sender) else { return }
+        toggleCollapseGroup(group)
+    }
+
+    @objc func showRenameGroupSheet(_ sender: Any?) {
+        guard let group = tabGroupFromSender(sender) else { return }
+        showManageGroupPopover(for: group)
+    }
+
+    // Chrome-style transient popover anchored to the group header chip. Name and
+    // colour edits apply live; the action rows reuse the same group operations as
+    // the context menu and close the popover.
+    @objc func showManageGroupPopover(for group: iTermTabGroup) {
+        let vc = iTermCreateTabGroupViewController(initialColor: group.color,
+                                                   initialName: group.name,
+                                                   manageMode: true)
+        let popover = NSPopover()
+        popover.behavior = .transient
+        popover.contentViewController = vc
+        // Match the window's light/dark theme so the popover never clashes with
+        // the active tab style (minimal, compact, dark, light, …).
+        popover.appearance = sheetAppearance
+        weak let weakPopover = popover
+
+        vc.onNameChange = { [weak self] name in
+            guard let self else { return }
+            group.name = name
+            group.headerTabViewItem.label = name
+            self.updateTabGroupDecorations()
+        }
+        vc.onColorChange = { [weak self] color in
+            guard let self else { return }
+            group.color = color
+            self.updateTabGroupDecorations()
+        }
+        vc.onNewTabInGroup = { [weak self] in
+            weakPopover?.close()
+            self?.newTab(inGroup: group)
+        }
+        vc.onUngroup = { [weak self] in
+            weakPopover?.close()
+            self?.deleteTabGroup(group)
+        }
+        vc.onCloseGroup = { [weak self] in
+            weakPopover?.close()
+            self?.closeGroup(group)
+        }
+
+        let tabBar = contentView.tabBarControl
+        var anchorRect = tabBar.frameOfCell(for: group.headerTabViewItem)
+        if anchorRect.isEmpty {
+            anchorRect = tabBar.bounds
+        }
+        popover.show(relativeTo: anchorRect, of: tabBar, preferredEdge: .maxY)
+    }
+
+    @objc func reconcileGroupsAfterReorder() {
+        guard !tabGroups.isEmpty else { return }
+        let tabView = contentView.tabView
+        for group in tabGroups where !group.isCollapsed {
+            let headerIndex = tabView.indexOfTabViewItem(group.headerTabViewItem)
+            guard headerIndex != NSNotFound, !group.memberTabIDs.isEmpty else { continue }
+
+            // Walk the span after the header. Members stay; a single foreign tab
+            // dropped between members joins (Chrome-style drag-in); members that no
+            // longer appear in the span were dragged out and leave the group.
+            var remaining = Set(group.memberTabIDs)
+            var newMemberIDs: [Int] = []
+            var pendingJoiner: Int?
+            var index = headerIndex + 1
+            while index < tabView.numberOfTabViewItems, !remaining.isEmpty {
+                guard let tab = tabView.tabViewItem(at: index).identifier as? PTYTab else {
+                    break
+                }
+                let tabID = Int(tab.uniqueId)
+                let belongsToOtherGroup = tabGroups.contains { $0 !== group && $0.memberTabIDs.contains(tabID) }
+                if remaining.contains(tabID) {
+                    if let joiner = pendingJoiner {
+                        newMemberIDs.append(joiner)
+                        pendingJoiner = nil
+                    }
+                    newMemberIDs.append(tabID)
+                    remaining.remove(tabID)
+                } else if belongsToOtherGroup || pendingJoiner != nil {
+                    break
+                } else {
+                    pendingJoiner = tabID
+                }
+                index += 1
+            }
+
+            if newMemberIDs.isEmpty {
+                deleteTabGroup(group)
+            } else if newMemberIDs != group.memberTabIDs {
+                group.memberTabIDs = newMemberIDs
+            }
+        }
+        updateTabGroupDecorations()
+    }
+
+    private func tabGroupFromSender(_ sender: Any?) -> iTermTabGroup? {
+        guard let item = sender as? NSMenuItem,
+              let group = item.representedObject as? iTermTabGroup else { return nil }
+        return group
+    }
+
+    private func unstashItems(for group: iTermTabGroup) {
+        let tabView = contentView.tabView
+        let headerIndex = tabView.indexOfTabViewItem(group.headerTabViewItem)
+        guard headerIndex != NSNotFound else { return }
+
+        contentView.tabBarControl.markNextInsertions(asAnimated:group.stashedTabViewItems.count)
+        for (offset, item) in group.stashedTabViewItems.enumerated() {
+            let targetIndex = headerIndex + 1 + offset
+            let safeIndex = min(targetIndex, tabView.numberOfTabViewItems)
+            tabView.insertTabViewItem(item, at: safeIndex)
+        }
+        group.stashedTabViewItems.removeAll()
+        group.isCollapsed = false
+    }
+
+    @objc func autoManageGroupCollapseForTab(_ tab: PTYTab) {
+        guard !groupCollapseManaging else { return }
+        groupCollapseManaging = true
+        defer { groupCollapseManaging = false }
+        let activeGroup = tabGroupForTab(tab)
+        for group in tabGroups {
+            if group === activeGroup {
+                if group.isCollapsed {
+                    expandGroup(group)
+                }
+            } else if !group.isCollapsed {
+                collapseGroup(group)
+            }
+        }
+    }
+
+    @objc func toggleCollapseGroup(_ group: iTermTabGroup) {
+        if group.isCollapsed {
+            expandGroup(group)
+        } else {
+            collapseGroup(group)
+        }
+    }
+
+    @objc func tabGroupForTab(_ tab: PTYTab) -> iTermTabGroup? {
+        let tabID = Int(tab.uniqueId)
+        return tabGroups.first { $0.memberTabIDs.contains(tabID) }
+    }
+
+    @objc func tabWillBeRemoved(_ tab: PTYTab) {
+        guard let group = tabGroupForTab(tab) else { return }
+        if group.isCollapsed {
+            group.stashedTabViewItems.removeAll { $0.identifier as? PTYTab === tab }
+        } else if currentTab() === tab {
+            // Pre-select another group member before NSTabView auto-selects outside the group,
+            // which would trigger autoManageGroupCollapseForTab and collapse the whole group.
+            let remainingIDs = group.memberTabIDs.filter { $0 != Int(tab.uniqueId) }
+            if let next = (tabs() ?? []).first(where: { remainingIDs.contains(Int($0.uniqueId)) }),
+               let item = next.tabViewItem {
+                contentView.tabView.selectTabViewItem(item)
+            }
+        }
+        removeTab(tab, fromGroup: group)
+    }
+
+    @objc func updateTabGroupDecorations() {
+        let tabBar = contentView.tabBarControl
+        let allCells = tabBar.cells()
+        let selectedTabID: Int? = currentTab().map { Int($0.uniqueId) }
+
+        for cell in allCells {
+            guard let psmCell = cell as? PSMTabBarCell,
+                  let tabViewItem = psmCell.representedObject as? NSTabViewItem else {
+                continue
+            }
+            if let group = tabViewItem.identifier as? iTermTabGroup {
+                psmCell.isGroupHeader = true
+                psmCell.isGroupMember = false
+                psmCell.isGroupCollapsed = group.isCollapsed
+                psmCell.isGroupActive = selectedTabID.map { group.memberTabIDs.contains($0) } ?? false
+                psmCell.groupName = group.name
+                psmCell.groupColor = group.color
+                psmCell.groupMemberCount = group.memberTabIDs.count
+            } else if let tab = tabViewItem.identifier as? PTYTab,
+                      let group = tabGroupForTab(tab) {
+                psmCell.isGroupHeader = false
+                psmCell.isGroupMember = true
+                psmCell.isGroupCollapsed = group.isCollapsed
+                psmCell.isGroupActive = false
+                psmCell.groupName = group.name
+                psmCell.groupColor = group.color
+                psmCell.groupMemberCount = group.memberTabIDs.count
+            } else {
+                psmCell.isGroupHeader = false
+                psmCell.isGroupMember = false
+                psmCell.isGroupCollapsed = false
+                psmCell.isGroupActive = false
+                psmCell.groupName = nil
+                psmCell.groupColor = nil
+                psmCell.groupMemberCount = 0
+            }
+        }
+        tabBar.needsDisplay = true
+    }
+
+    @objc func encodeTabGroupsForArrangement() -> [[String: Any]] {
+        let allTabs = tabs() ?? []
+        return tabGroups.map { $0.toDictionary(allTabs: allTabs) }
+    }
+
+    @objc func restoreTabGroupsFromArrangement(_ arrangement: [[String: Any]]) {
+        let allTabs = tabs() ?? []
+        for dict in arrangement {
+            guard let group = iTermTabGroup(dictionary: dict) else { continue }
+            let resolvedIDs = group.memberTabIDs.compactMap { index -> Int? in
+                guard index >= 0, index < allTabs.count else { return nil }
+                return Int(allTabs[index].uniqueId)
+            }
+            guard !resolvedIDs.isEmpty else { continue }
+            group.memberTabIDs = resolvedIDs
+
+            if let firstTab = allTabs.first(where: { resolvedIDs.first == Int($0.uniqueId) }),
+               let firstItem = firstTab.tabViewItem {
+                let idx = contentView.tabView.indexOfTabViewItem(firstItem)
+                if idx != NSNotFound {
+                    contentView.tabView.insertTabViewItem(group.headerTabViewItem, at: idx)
+                }
+            }
+
+            let shouldCollapse = group.isCollapsed
+            group.isCollapsed = false
+            mutableTabGroups.add(group)
+            if shouldCollapse {
+                collapseGroupSilently(group)
+            }
+        }
+        updateTabGroupDecorations()
+    }
+
+    @objc func collapseGroupSilently(_ group: iTermTabGroup) {
+        let memberTabs = group.memberTabIDs.compactMap { id in
+            (tabs() ?? []).first { Int($0.uniqueId) == id }
+        }
+        for tab in memberTabs {
+            guard let item = tab.tabViewItem else { continue }
+            contentView.tabView.removeTabViewItem(item)
+            group.stashedTabViewItems.append(item)
+        }
+        group.isCollapsed = true
+    }
+
+    @objc func expandGroupSilently(_ group: iTermTabGroup) {
+        let tabView = contentView.tabView
+        let headerIndex = tabView.indexOfTabViewItem(group.headerTabViewItem)
+        guard headerIndex != NSNotFound else { return }
+        contentView.tabBarControl.markNextInsertions(asAnimated:group.stashedTabViewItems.count)
+        for (offset, item) in group.stashedTabViewItems.enumerated() {
+            let targetIndex = headerIndex + 1 + offset
+            let safeIndex = min(targetIndex, tabView.numberOfTabViewItems)
+            tabView.insertTabViewItem(item, at: safeIndex)
+        }
+        group.stashedTabViewItems.removeAll()
+        group.isCollapsed = false
+    }
+
+    @objc func showCreateTabGroupSheet(forTab tab: PTYTab) {
+        showCreateTabGroupSheet(forTab: tab, completion: nil)
+    }
+
+    @objc(showCreateTabGroupSheetForTab:completion:) func showCreateTabGroupSheet(forTab tab: PTYTab, completion: ((iTermTabGroup) -> Void)?) {
+        let vc = iTermCreateTabGroupViewController()
+        let panel = NSPanel(contentRect: NSRect(x: 0, y: 0, width: 340, height: 180),
+                            styleMask: [.titled, .docModalWindow],
+                            backing: .buffered,
+                            defer: false)
+        panel.appearance = sheetAppearance
+        panel.contentViewController = vc
+        vc.completion = { [weak self, weak panel] result in
+            guard let self, let panel else { return }
+            self.window?.endSheet(panel)
+            guard let (name, color) = result else { return }
+            let group = self.createTabGroup(name: name, color: color, forTab: tab)
+            completion?(group)
+        }
+        window?.beginSheet(panel) { _ in }
+    }
+
+    @objc func addTabToNewGroup(_ sender: Any?) {
+        guard let tab = tabFromSender(sender) else { return }
+        showCreateTabGroupSheet(forTab: tab)
+    }
+
+    @objc func moveTabToGroup(_ sender: Any?) {
+        guard let item = sender as? NSMenuItem,
+              let dict = item.representedObject as? [String: AnyObject],
+              let tabViewItem = dict["tabViewItem"] as? NSTabViewItem,
+              let tab = tabViewItem.identifier as? PTYTab,
+              let group = dict["group"] as? iTermTabGroup else { return }
+        if let currentGroup = tabGroupForTab(tab), currentGroup === group { return }
+        if let currentGroup = tabGroupForTab(tab) {
+            removeTab(tab, fromGroup: currentGroup)
+        }
+        addTab(tab, toGroup: group)
+        autoManageGroupCollapseForTab(tab)
+    }
+
+    @objc func removeTabFromGroup(_ sender: Any?) {
+        guard let tab = tabFromSender(sender),
+              let group = tabGroupForTab(tab) else { return }
+        removeTab(tab, fromGroup: group)
+    }
+
+    private func tabFromSender(_ sender: Any?) -> PTYTab? {
+        guard let item = sender as? NSMenuItem,
+              let tabViewItem = item.representedObject as? NSTabViewItem else { return nil }
+        return tabViewItem.identifier as? PTYTab
+    }
+
+    private func collapseGroup(_ group: iTermTabGroup) {
+        let allTabs = tabs() ?? []
+        let memberTabs = group.memberTabIDs.compactMap { id in allTabs.first { Int($0.uniqueId) == id } }
+        guard !memberTabs.isEmpty else { return }
+
+        let wasManaging = groupCollapseManaging
+        groupCollapseManaging = true
+        defer { groupCollapseManaging = wasManaging }
+
+        if let selected = currentTab(), group.memberTabIDs.contains(Int(selected.uniqueId)) {
+            selectNearestTabOutside(group: group)
+        }
+
+        group.isCollapsed = true
+        let itemsToStash = memberTabs.compactMap { $0.tabViewItem }
+        updateTabGroupDecorations()
+
+        contentView.tabBarControl.beginCollapseAnimation(for: itemsToStash) { [weak self] in
+            guard let self else { return }
+            for item in itemsToStash {
+                self.contentView.tabView.removeTabViewItem(item)
+                group.stashedTabViewItems.append(item)
+            }
+            self.contentView.tabBarControl.update(true)
+        }
+    }
+
+    private func selectNearestTabOutside(group: iTermTabGroup) {
+        let tabView = contentView.tabView
+        let headerIndex = tabView.indexOfTabViewItem(group.headerTabViewItem)
+        guard headerIndex != NSNotFound else { return }
+        let groupSize = group.memberTabIDs.count
+        let afterGroupIndex = headerIndex + groupSize + 1
+
+        for i in afterGroupIndex..<tabView.numberOfTabViewItems {
+            let item = tabView.tabViewItem(at: i)
+            if item.identifier is PTYTab {
+                tabView.selectTabViewItem(item)
+                return
+            }
+        }
+        for i in stride(from: headerIndex - 1, through: 0, by: -1) {
+            let item = tabView.tabViewItem(at: i)
+            if item.identifier is PTYTab {
+                tabView.selectTabViewItem(item)
+                return
+            }
+        }
+    }
+
+    private func expandGroup(_ group: iTermTabGroup) {
+        // If a collapse animation is in-flight for this group, finish it synchronously
+        // so stashedTabViewItems is populated before we try to expand.
+        contentView.tabBarControl.cancelCollapseAnimation()
+
+        let tabView = contentView.tabView
+        let headerIndex = tabView.indexOfTabViewItem(group.headerTabViewItem)
+        guard headerIndex != NSNotFound else { return }
+
+        group.isCollapsed = false
+        let itemsToInsert = group.stashedTabViewItems
+        group.stashedTabViewItems.removeAll()
+        contentView.tabBarControl.markNextInsertions(asAnimated:itemsToInsert.count)
+        for (offset, item) in itemsToInsert.enumerated() {
+            let targetIndex = headerIndex + 1 + offset
+            let safeIndex = min(targetIndex, tabView.numberOfTabViewItems)
+            tabView.insertTabViewItem(item, at: safeIndex)
+        }
+        contentView.tabBarControl.update(true)
+        updateTabGroupDecorations()
+    }
+
+    @objc func enforceContiguityOfAllGroups() {
+        for group in tabGroups where !group.isCollapsed {
+            enforceContiguity(of: group)
+        }
+        updateTabGroupDecorations()
+    }
+
+    private func enforceContiguity(of group: iTermTabGroup) {
+        guard !group.memberTabIDs.isEmpty else { return }
+        let allTabs = tabs() ?? []
+        let memberTabs = group.memberTabIDs.compactMap { id in allTabs.first { Int($0.uniqueId) == id } }
+
+        let tabView = contentView.tabView
+        let headerIndex = tabView.indexOfTabViewItem(group.headerTabViewItem)
+        guard headerIndex != NSNotFound else { return }
+
+        for (i, tab) in memberTabs.enumerated() {
+            guard let item = tab.tabViewItem else { continue }
+            let currentIndex = tabView.indexOfTabViewItem(item)
+            let targetIndex = headerIndex + 1 + i
+            if currentIndex != targetIndex {
+                tabView.removeTabViewItem(item)
+                let safeTarget = min(targetIndex, tabView.numberOfTabViewItems)
+                tabView.insertTabViewItem(item, at: safeTarget)
+            }
+        }
+    }
+}
diff --git a/sources/TerminalView/PseudoTerminal.h b/sources/TerminalView/PseudoTerminal.h
index 99aff56294..dd78d66a3d 100644
--- a/sources/TerminalView/PseudoTerminal.h
+++ b/sources/TerminalView/PseudoTerminal.h
@@ -18,6 +18,7 @@
 #import "PTYWindow.h"
 #import "WindowControllerInterface.h"
 #import "iTermSessionRestorationStatusProtocol.h"
+#import "iTermRootTerminalView.h"
 
 #include "iTermFileDescriptorClient.h"
 
@@ -27,6 +28,8 @@
 @class iTermBrowserWebView;
 @class iTermPromptOnCloseReason;
 @class iTermSessionFactory;
+@class iTermTabGroup;
+
 @class iTermToolbeltView;
 @protocol iTermLargeContentProvider;
 @protocol iTermWindowScope;
@@ -85,6 +88,9 @@ extern NSString *const iTermDidCreateTerminalWindowNotification;
 // Indicates if the window is fully initialized.
 @property(nonatomic, readonly) BOOL windowInitialized;
 
+// The window's root content view. Typed here for convenience.
+@property(nonatomic, readonly) __unsafe_unretained iTermRootTerminalView *contentView;
+
 // If the window is "anchored" to a screen, this returns that screen. Otherwise, it returns the
 // current screen. If the window doesn't have a current screen, it returns the
 // preferred screen from the profile. If headless, this returns nil. Consider
@@ -459,3 +465,16 @@ extern NSString *const iTermDidCreateTerminalWindowNotification;
 
 @end
 
+// Tab groups for inline tab organization. Implemented in PseudoTerminal+TabGroups.swift.
+@interface PseudoTerminal (TabGroups)
+@property(nonatomic, readonly) NSArray<iTermTabGroup *> *tabGroups;
+- (void)addTabToNewGroup:(id)sender;
+- (void)moveTabToGroup:(id)sender;
+- (void)removeTabFromGroup:(id)sender;
+- (void)showCreateTabGroupSheetForTab:(PTYTab *)tab completion:(void (^)(iTermTabGroup *))completion;
+- (void)addTab:(PTYTab *)tab toGroup:(iTermTabGroup *)group;
+- (void)newTabInGroup:(id)sender;
+- (void)closeTabGroup:(id)sender;
+- (void)toggleCollapseGroupFromMenu:(id)sender;
+@end
+
diff --git a/sources/TerminalView/PseudoTerminal.m b/sources/TerminalView/PseudoTerminal.m
index f243eeb01c..b019036435 100644
--- a/sources/TerminalView/PseudoTerminal.m
+++ b/sources/TerminalView/PseudoTerminal.m
@@ -203,6 +203,23 @@
 NSString *const TERMINAL_ARRANGEMENT_MINIATURIZED = @"miniaturized";
 NSString *const TERMINAL_ARRANGEMENT_SIZE_LOCKED = @"Size Locked";
 
+static NSString *iTermColorNameForGroupColor(NSColor *color) {
+    NSColor *srgb = [color colorUsingColorSpace:NSColorSpace.sRGBColorSpace];
+    if (!srgb) return @"Group";
+    CGFloat h = 0, s = 0, b = 0, a = 0;
+    [srgb getHue:&h saturation:&s brightness:&b alpha:&a];
+    h *= 360.0;
+    if (s < 0.25) return @"Grey";
+    if (h < 15 || h >= 345) return @"Red";
+    if (h < 45) return @"Orange";
+    if (h < 75) return @"Yellow";
+    if (h < 150) return @"Green";
+    if (h < 195) return @"Teal";
+    if (h < 255) return @"Blue";
+    if (h < 300) return @"Purple";
+    return @"Pink";
+}
+
 static void iTermPercentageSanitize(iTermPercentage *percentage) {
     if (percentage->width >= 0) {
         if (percentage->width <= 0 || percentage->width > 100) {
@@ -439,6 +456,8 @@ @implementation PseudoTerminal {
     CGFloat _rightExtraWindowGrowthDelta;
     BOOL _excursionPrevented;
 
+    NSMutableArray<iTermTabGroup *> *_mutableTabGroups;
+
 }
 
 @synthesize scope = _scope;
@@ -464,10 +483,15 @@ - (instancetype)initWithWindowNibName:(NSString *)windowNibName {
     if (self) {
         _automaticallySelectNewTabs = YES;
         self.autoCommandHistorySessionGuid = nil;
+        _mutableTabGroups = [[NSMutableArray alloc] init];
     }
     return self;
 }
 
+- (NSMutableArray *)mutableTabGroups {
+    return _mutableTabGroups;
+}
+
 - (instancetype)initWithSmartLayout:(BOOL)smartLayout
                          windowType:(iTermWindowType)windowType
                     savedWindowType:(iTermWindowType)savedWindowType
@@ -1103,6 +1127,7 @@ - (void)dealloc {
     [_fullScreenEnteredSeal release];
     [_windowSizeHelper release];
     [_titlebarAccessoryNanny release];
+    [_mutableTabGroups release];
 
     [super dealloc];
 }
@@ -2263,6 +2288,7 @@ - (iTermRestorableSession *)restorableSessionForTab:(PTYTab *)aTab {
 // tab, and closes the window if there are no tabs left.
 - (void)removeTab:(PTYTab *)aTab {
     DLog(@"Remove tab %@", aTab);
+    [self tabWillBeRemoved:aTab];
     if (![aTab isTmuxTab]) {
         // Exit synthetic sessions (filter, instant replay, screenshot mode)
         // so the restorable session captures live sessions that can be revived.
@@ -3996,6 +4022,10 @@ - (BOOL)restoreTabsFromArrangement:(NSDictionary *)arrangement
         return NO;
     }
     [self updateUseTransparency];
+    NSArray *groupDicts = arrangement[@"Tab Groups"];
+    if (groupDicts) {
+        [self restoreTabGroupsFromArrangement:groupDicts];
+    }
     return YES;
 }
 
@@ -4115,34 +4145,53 @@ - (BOOL)populateArrangementWith:(iTermOr<NSArray<PTYTab *> *, PTYSession *> *)ta
                         encoder:(id<iTermEncoderAdapter>)result {
     NSRect rect = [[self window] frame];
 
-    return [PseudoTerminal populateArrangementWith:tabsOrSession
-                                 includingContents:includeContents
-                                           encoder:result
-                                      terminalGuid:self.terminalGuid
-                                              rect:rect
-                                   useTransparency:useTransparency_
-                                shouldShowToolbelt:_contentView.shouldShowToolbelt
-                               toolbeltProportions:_contentView.toolbelt.proportions
-                           toolbeltRestorableState:_contentView.toolbelt.restorableState
-                         windowTitleOverrideFormat:self.scope.windowTitleOverrideFormat
-                  hidingToolbeltShouldResizeWindow:hidingToolbeltShouldResizeWindow_
-                                     anyFullScreen:[self anyFullScreen]
-                                    lionFullScreen:[self lionFullScreen]
-                                          oldFrame:oldFrame_
-                                        windowType:self.windowType
-                                   savedWindowType:self.savedWindowType
-                                        percentage:_percentage
-                                    initialProfile:[self expurgatedInitialProfile]
-                                    isHotKeyWindow:self.isHotKeyWindow
-                                  hotkeyWindowType:_hotkeyWindowType
-                                       screenIndex:[[NSScreen screens] indexOfObjectIdenticalTo:[[self window] screen]]
-                      screenNumberFromFirstProfile:_windowPositioner.screenNumberFromFirstProfile
-                                  windowSizeHelper:_windowSizeHelper
-                                  hideAfterOpening:hideAfterOpening_
-                                  selectedTabIndex:[_contentView.tabView indexOfTabViewItem:[_contentView.tabView selectedTabViewItem]]
-                                               tab:nil
-                                       profileGuid:[[[[iTermHotKeyController sharedInstance] profileHotKeyForWindowController:self] profile] objectForKey:KEY_GUID]
-                                       isMaximized:[self isMaximized]];
+    NSMutableArray<iTermTabGroup *> *collapsedGroups = [NSMutableArray array];
+    for (iTermTabGroup *group in self.tabGroups) {
+        if (group.isCollapsed) {
+            [collapsedGroups addObject:group];
+            [self expandGroupSilently:group];
+        }
+    }
+
+    const BOOL ok = [PseudoTerminal populateArrangementWith:tabsOrSession
+                                          includingContents:includeContents
+                                                    encoder:result
+                                               terminalGuid:self.terminalGuid
+                                                       rect:rect
+                                            useTransparency:useTransparency_
+                                         shouldShowToolbelt:_contentView.shouldShowToolbelt
+                                        toolbeltProportions:_contentView.toolbelt.proportions
+                                    toolbeltRestorableState:_contentView.toolbelt.restorableState
+                                  windowTitleOverrideFormat:self.scope.windowTitleOverrideFormat
+                           hidingToolbeltShouldResizeWindow:hidingToolbeltShouldResizeWindow_
+                                              anyFullScreen:[self anyFullScreen]
+                                             lionFullScreen:[self lionFullScreen]
+                                                   oldFrame:oldFrame_
+                                                 windowType:self.windowType
+                                            savedWindowType:self.savedWindowType
+                                                 percentage:_percentage
+                                             initialProfile:[self expurgatedInitialProfile]
+                                             isHotKeyWindow:self.isHotKeyWindow
+                                           hotkeyWindowType:_hotkeyWindowType
+                                                screenIndex:[[NSScreen screens] indexOfObjectIdenticalTo:[[self window] screen]]
+                               screenNumberFromFirstProfile:_windowPositioner.screenNumberFromFirstProfile
+                                           windowSizeHelper:_windowSizeHelper
+                                           hideAfterOpening:hideAfterOpening_
+                                           selectedTabIndex:[_contentView.tabView indexOfTabViewItem:[_contentView.tabView selectedTabViewItem]]
+                                                        tab:nil
+                                                profileGuid:[[[[iTermHotKeyController sharedInstance] profileHotKeyForWindowController:self] profile] objectForKey:KEY_GUID]
+                                                isMaximized:[self isMaximized]];
+    for (iTermTabGroup *group in collapsedGroups) {
+        [self collapseGroupSilently:group];
+    }
+
+    if (ok) {
+        NSArray *groupDicts = [self encodeTabGroupsForArrangement];
+        if (groupDicts.count > 0) {
+            result[@"Tab Groups"] = groupDicts;
+        }
+    }
+    return ok;
 }
 
 + (BOOL)populateArrangementWith:(iTermOr<NSArray<PTYTab *> *, PTYSession *> *)tabsOrSession
@@ -5482,7 +5531,8 @@ - (NSSize)windowWillResize:(NSWindow *)sender toSize:(NSSize)proposedFrameSize {
                                     rightExtra:self.currentSession.desiredRightExtra];
     // Respect minimum tab sizes.
     for (NSTabViewItem* tabViewItem in [_contentView.tabView tabViewItems]) {
-        PTYTab* theTab = [tabViewItem identifier];
+        PTYTab* theTab = tabViewItem.it_tab;
+        if (!theTab) { continue; }
         NSSize minTabSize = [theTab minSize];
         tabSize.width = MAX(tabSize.width, minTabSize.width);
         tabSize.height = MAX(tabSize.height, minTabSize.height);
@@ -6892,12 +6942,15 @@ - (void)reallyDisableBlurIfNeeded {
 
 - (void)tabView:(NSTabView *)tabView didSelectTabViewItem:(NSTabViewItem *)tabViewItem {
     DLog(@"Did select tab view %@", tabViewItem);
+    PTYTab *tab = tabViewItem.it_tab;
+    if (!tab) {
+        return;
+    }
     [_contentView.tabBarControl setFlashing:YES];
 
     if (self.autoCommandHistorySessionGuid) {
         [self hideAutoCommandHistory];
     }
-    PTYTab *tab = [tabViewItem identifier];
     for (PTYSession *aSession in [tab sessions]) {
         DLog(@"Clear new-output flag in %@", aSession);
         [aSession setNewOutput:NO];
@@ -6983,6 +7036,11 @@ - (void)tabView:(NSTabView *)tabView didSelectTabViewItem:(NSTabViewItem *)tabVi
     [_contentView setCurrentSessionAlpha:self.currentSession.textview.transparencyAlpha];
     [tab didSelectTab];
     [[NSNotificationCenter defaultCenter] postNotificationName:iTermSelectedTabDidChange object:tab];
+
+    [self autoManageGroupCollapseForTab:tab];
+    if (self.tabGroups.count > 0) {
+        [self updateTabGroupDecorations];
+    }
     DLog(@"Finished");
 }
 
@@ -7101,20 +7159,24 @@ - (void)saveAffinitiesLater:(PTYTab *)theTab {
 }
 
 - (void)tabView:(NSTabView *)tabView willRemoveTabViewItem:(NSTabViewItem *)tabViewItem {
-    [self saveAffinitiesLater:[tabViewItem identifier]];
+    PTYTab *tab = tabViewItem.it_tab;
+    if (!tab) { return; }
+    [self saveAffinitiesLater:tab];
 }
 
 - (void)tabView:(NSTabView *)tabView willAddTabViewItem:(NSTabViewItem *)tabViewItem {
-
+    PTYTab *tab = tabViewItem.it_tab;
+    if (!tab) { return; }
     [self tabView:tabView willInsertTabViewItem:tabViewItem atIndex:[tabView numberOfTabViewItems]];
-    [self saveAffinitiesLater:[tabViewItem identifier]];
+    [self saveAffinitiesLater:tab];
 }
 
 - (void)tabView:(NSTabView *)tabView
     willInsertTabViewItem:(NSTabViewItem *)tabViewItem
         atIndex:(int)anIndex {
     DLog(@"%@: tabView:%@ willInsertTabViewItem:%@ atIndex:%d", self, tabView, tabViewItem, anIndex);
-    PTYTab* theTab = [tabViewItem identifier];
+    PTYTab* theTab = tabViewItem.it_tab;
+    if (!theTab) { return; }
     [theTab setParentWindow:self];
     theTab.delegate = self;
 #if BETA
@@ -7225,7 +7287,8 @@ - (BOOL)tabView:(NSTabView*)aTabView
 - (void)tabView:(NSTabView*)aTabView
     willDropTabViewItem:(NSTabViewItem *)tabViewItem
                inTabBar:(PSMTabBarControl *)aTabBarControl {
-    PTYTab *aTab = [tabViewItem identifier];
+    PTYTab *aTab = tabViewItem.it_tab;
+    if (!aTab) { return; }
     for (PTYSession* aSession in [aTab sessions]) {
         [aSession setIgnoreResizeNotifications:YES];
     }
@@ -7260,7 +7323,8 @@ - (void)updateTabObjectCounts {
 - (void)tabView:(NSTabView*)aTabView
     didDropTabViewItem:(NSTabViewItem *)tabViewItem
               inTabBar:(PSMTabBarControl *)aTabBarControl {
-    PTYTab *aTab = [tabViewItem identifier];
+    PTYTab *aTab = tabViewItem.it_tab;
+    if (!aTab) { return; }
     PseudoTerminal *term = (PseudoTerminal *)[aTabBarControl delegate];
     [self didDonateTab:aTab toWindowController:term];
 }
@@ -7401,7 +7465,7 @@ - (void)tabViewDidChangeNumberOfTabViewItems:(NSTabView *)tabView {
         PtyLog(@"tabViewDidChangeNumberOfTabViewItems - calling fitWindowToTab");
 
         NSTabViewItem *tabViewItem = [[_contentView.tabView tabViewItems] objectAtIndex:0];
-        PTYTab *firstTab = [tabViewItem identifier];
+        PTYTab *firstTab = tabViewItem.it_tab ?: [self tabs].firstObject;
 
         NSPoint originalOrigin = self.window.frame.origin;
         if (wasDraggedFromAnotherWindow_) {
@@ -7583,6 +7647,7 @@ - (NSMenu *)tabView:(NSTabView *)tabView menuForTabViewItem:(NSTabViewItem *)tab
         NSMenu *tabMenu = [[[NSMenu alloc] initWithTitle:@""] autorelease];
         NSUInteger count = 1;
         for (NSTabViewItem *aTabViewItem in [_contentView.tabView tabViewItems]) {
+            if (!aTabViewItem.it_tab) { continue; }
             NSString *title = [NSString stringWithFormat:@"%@ #%ld", [aTabViewItem label], (unsigned long)count++];
             item = [[[NSMenuItem alloc] initWithTitle:title
                                                action:@selector(selectTab:)
@@ -7694,6 +7759,43 @@ - (NSMenu *)tabView:(NSTabView *)tabView menuForTabViewItem:(NSTabViewItem *)tab
         [rootMenu addItem:item];
     }
 
+    // tab groups
+    [rootMenu addItem:[NSMenuItem separatorItem]];
+    NSMenuItem *addToGroupItem = [[[NSMenuItem alloc] initWithTitle:@"Add to New Group\u2026"
+                                                             action:@selector(addTabToNewGroup:)
+                                                      keyEquivalent:@""] autorelease];
+    [addToGroupItem setRepresentedObject:tabViewItem];
+    [addToGroupItem setTarget:self];
+    [rootMenu addItem:addToGroupItem];
+
+    if (self.tabGroups.count > 0) {
+        NSMenu *moveMenu = [[[NSMenu alloc] initWithTitle:@""] autorelease];
+        for (iTermTabGroup *group in self.tabGroups) {
+            NSString *groupTitle = group.name.length > 0 ? group.name : iTermColorNameForGroupColor(group.color);
+            NSMenuItem *groupItem = [[[NSMenuItem alloc] initWithTitle:groupTitle
+                                                               action:@selector(moveTabToGroup:)
+                                                        keyEquivalent:@""] autorelease];
+            [groupItem setRepresentedObject:@{@"tabViewItem": tabViewItem, @"group": group}];
+            [groupItem setTarget:self];
+            [moveMenu addItem:groupItem];
+        }
+        NSMenuItem *moveItem = [[[NSMenuItem alloc] initWithTitle:@"Move to Group"
+                                                           action:nil
+                                                    keyEquivalent:@""] autorelease];
+        [rootMenu addItem:moveItem];
+        [rootMenu setSubmenu:moveMenu forItem:moveItem];
+    }
+
+    PTYTab *contextMenuTab = [tabViewItem identifier];
+    if ([self tabGroupForTab:contextMenuTab] != nil) {
+        NSMenuItem *removeItem = [[[NSMenuItem alloc] initWithTitle:@"Remove from Group"
+                                                             action:@selector(removeTabFromGroup:)
+                                                      keyEquivalent:@""] autorelease];
+        [removeItem setRepresentedObject:tabViewItem];
+        [removeItem setTarget:self];
+        [rootMenu addItem:removeItem];
+    }
+
     // add label
     [rootMenu addItem: [NSMenuItem separatorItem]];
     NSSize tabColorViewSize = [ColorsMenuItemView preferredSize];
@@ -7987,8 +8089,129 @@ - (void)tabViewDoubleClickTabBar:(NSTabView *)tabView {
     [itad newSession:nil];
 }
 
+- (NSMenu *)tabView:(NSTabView *)tabView menuForGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem {
+    iTermTabGroup *group = tabViewItem.identifier;
+    if (![group isKindOfClass:[iTermTabGroup class]]) {
+        return nil;
+    }
+    NSMenu *menu = [[[NSMenu alloc] initWithTitle:@""] autorelease];
+
+    NSMenuItem *newTabItem = [[[NSMenuItem alloc] initWithTitle:@"New Tab in Group"
+                                                         action:@selector(newTabInGroup:)
+                                                  keyEquivalent:@""] autorelease];
+    [newTabItem setRepresentedObject:group];
+    [newTabItem setTarget:self];
+    [menu addItem:newTabItem];
+
+    NSMenuItem *collapseItem = [[[NSMenuItem alloc] initWithTitle:group.isCollapsed ? @"Expand Group" : @"Collapse Group"
+                                                           action:@selector(toggleCollapseGroupFromMenu:)
+                                                    keyEquivalent:@""] autorelease];
+    [collapseItem setRepresentedObject:group];
+    [collapseItem setTarget:self];
+    [menu addItem:collapseItem];
+
+    [menu addItem:[NSMenuItem separatorItem]];
+
+    NSMenuItem *editItem = [[[NSMenuItem alloc] initWithTitle:@"Edit Group…"
+                                                        action:@selector(showRenameGroupSheet:)
+                                                 keyEquivalent:@""] autorelease];
+    [editItem setRepresentedObject:group];
+    [editItem setTarget:self];
+    [menu addItem:editItem];
+
+    NSMenuItem *ungroupItem = [[[NSMenuItem alloc] initWithTitle:@"Ungroup"
+                                                          action:@selector(ungroupTabs:)
+                                                   keyEquivalent:@""] autorelease];
+    [ungroupItem setRepresentedObject:group];
+    [ungroupItem setTarget:self];
+    [menu addItem:ungroupItem];
+
+    [menu addItem:[NSMenuItem separatorItem]];
+
+    NSMenuItem *closeItem = [[[NSMenuItem alloc] initWithTitle:@"Close Group"
+                                                        action:@selector(closeTabGroup:)
+                                                 keyEquivalent:@""] autorelease];
+    [closeItem setRepresentedObject:group];
+    [closeItem setTarget:self];
+    [menu addItem:closeItem];
+
+    return menu;
+}
+
+- (void)tabView:(NSTabView *)tabView doubleClickGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem {
+    iTermTabGroup *group = tabViewItem.identifier;
+    if (![group isKindOfClass:[iTermTabGroup class]]) {
+        return;
+    }
+    // Hold the guard so that tabView:didSelectTabViewItem: doesn't run
+    // autoManageGroupCollapseForTab mid-operation and undo our expand.
+    self.groupCollapseManaging = YES;
+    [self toggleCollapseGroup:group];
+    self.groupCollapseManaging = NO;
+
+    if (!group.isCollapsed) {
+        PTYTab *firstMember = nil;
+        for (PTYTab *tab in [self tabs]) {
+            if ([group.memberTabIDs containsObject:@(tab.uniqueId)]) {
+                firstMember = tab;
+                break;
+            }
+        }
+        if (firstMember) {
+            // Collapse other groups first, then select so the selection sticks.
+            [self autoManageGroupCollapseForTab:firstMember];
+            if (firstMember.tabViewItem) {
+                [_contentView.tabView selectTabViewItem:firstMember.tabViewItem];
+            }
+        }
+    }
+}
+
+- (void)tabView:(NSTabView *)tabView groupTabViewItems:(NSArray<NSTabViewItem *> *)tabViewItems {
+    NSMutableArray<PTYTab *> *tabs = [NSMutableArray array];
+    for (NSTabViewItem *item in tabViewItems) {
+        PTYTab *tab = item.it_tab;
+        if (tab) {
+            [tabs addObject:tab];
+        }
+    }
+    if (tabs.count < 2) { return; }
+    PTYTab *firstTab = tabs.firstObject;
+    [self showCreateTabGroupSheetForTab:firstTab completion:^(iTermTabGroup *group) {
+        if (!group) { return; }
+        for (NSUInteger i = 1; i < tabs.count; i++) {
+            [self addTab:tabs[i] toGroup:group];
+        }
+    }];
+}
+
+- (void)tabView:(NSTabView *)tabView willBeginDraggingGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem {
+    iTermTabGroup *group = tabViewItem.identifier;
+    if (![group isKindOfClass:[iTermTabGroup class]]) {
+        return;
+    }
+    if (!group.isCollapsed) {
+        self.groupCollapseManaging = YES;
+        [self collapseGroupSilently:group];
+        self.groupCollapseManaging = NO;
+        [self updateTabGroupDecorations];
+        [_contentView.tabBarControl update];
+    }
+}
+
+- (void)tabView:(NSTabView *)tabView didClickGroupHeaderTabViewItem:(NSTabViewItem *)tabViewItem {
+    iTermTabGroup *group = tabViewItem.identifier;
+    if (![group isKindOfClass:[iTermTabGroup class]]) {
+        return;
+    }
+    // Single click on the group chip opens the management popover (Chrome-style);
+    // double click toggles collapse (see doubleClickGroupHeaderTabViewItem:).
+    [self showManageGroupPopoverFor:group];
+}
+
 - (void)tabView:(NSTabView *)tabView updateStateForTabViewItem:(NSTabViewItem *)tabViewItem {
-    PTYTab *tab = tabViewItem.identifier;
+    PTYTab *tab = tabViewItem.it_tab;
+    if (!tab) { return; }
     [_contentView.tabBarControl setIsProcessing:tab.isProcessing forTabWithIdentifier:tab];
     [_contentView.tabBarControl setProgress:(PSMProgress)tab.progress
                        forTabWithIdentifier:tab];
@@ -8178,6 +8401,13 @@ + (BOOL)titleBarShouldAppearTransparentForWindowType:(iTermWindowType)windowType
 
 
 - (void)tabsDidReorder {
+    PSMTabBarControl *tabBar = self.contentView.tabBarControl;
+    if (tabBar.lastDragWasGroupHeader) {
+        tabBar.lastDragWasGroupHeader = NO;
+        [self enforceContiguityOfAllGroups];
+    } else {
+        [self reconcileGroupsAfterReorder];
+    }
     TmuxController *controller = nil;
     NSMutableArray *windowIds = [NSMutableArray array];
 
@@ -9779,7 +10009,8 @@ - (NSSize)sizeOfLargestTabWithExclusion:(PseudoTerminalTabSizeExclusion)exclusio
     PtyLog(@"fitWindowToTabs.......");
     DLog(@"Finding the biggest tab:");
     for (NSTabViewItem* item in [_contentView.tabView tabViewItems]) {
-        PTYTab* tab = [item identifier];
+        PTYTab* tab = item.it_tab;
+        if (!tab) { continue; }
         switch (exclusion) {
             case PseudoTerminalTabSizeExclusionTmux:
                 if (tab.isTmuxTab) {
@@ -10220,7 +10451,8 @@ - (float)minWidth
     // Pick 400 as an absolute minimum just to be safe. This is rather arbitrary and hacky.
     float minWidth = 400;
     for (NSTabViewItem* tabViewItem in [_contentView.tabView tabViewItems]) {
-        PTYTab* theTab = [tabViewItem identifier];
+        PTYTab* theTab = tabViewItem.it_tab;
+        if (!theTab) { continue; }
         minWidth = MAX(minWidth, [theTab minSize].width);
     }
     return minWidth;
@@ -10284,7 +10516,10 @@ - (void)addTabAtAutomaticallyDeterminedLocation:(PTYTab *)tab {
     NSMutableArray<PTYTab *> *tabs = [NSMutableArray arrayWithCapacity:n];
     for (int i = 0; i < n; ++i) {
         NSTabViewItem* theItem = [_contentView.tabView tabViewItemAtIndex:i];
-        [tabs addObject:[theItem identifier]];
+        PTYTab *tab = theItem.it_tab;
+        if (tab) {
+            [tabs addObject:tab];
+        }
     }
     return tabs;
 }
@@ -10605,7 +10840,8 @@ - (void)refreshTerminal:(NSNotification *)aNotification {
     // formerly countless tabs show their counts.
     BOOL needResize = NO;
     for (int i = 0; i < [_contentView.tabView numberOfTabViewItems]; ++i) {
-        PTYTab *aTab = [[_contentView.tabView tabViewItemAtIndex:i] identifier];
+        PTYTab *aTab = [_contentView.tabView tabViewItemAtIndex:i].it_tab;
+        if (!aTab) { continue; }
         if ([aTab updatePaneTitles]) {
             needResize = YES;
         }
@@ -12200,7 +12436,9 @@ - (IBAction)enableSendInputToAllTabs:(id)sender {
 - (void)fitTabsToWindow {
     PtyLog(@"fitTabsToWindow begins");
     for (int i = 0; i < [_contentView.tabView numberOfTabViewItems]; ++i) {
-        [self fitTabToWindow:[[_contentView.tabView tabViewItemAtIndex:i] identifier]];
+        PTYTab *tab = [_contentView.tabView tabViewItemAtIndex:i].it_tab;
+        if (!tab) { continue; }
+        [self fitTabToWindow:tab];
     }
     PtyLog(@"fitTabsToWindow returns");
 }
@@ -12521,7 +12759,8 @@ - (long long)timestampForFraction:(float)f
 - (NSArray<PTYSession *> *)allSessions {
     NSMutableArray* result = [NSMutableArray arrayWithCapacity:[_contentView.tabView numberOfTabViewItems]];
     for (NSTabViewItem* item in [_contentView.tabView tabViewItems]) {
-        PTYTab *tab = [item identifier];
+        PTYTab *tab = item.it_tab;
+        if (!tab) { continue; }
         [result addObjectsFromArray:[tab sessions]];
     }
     return result;
@@ -13663,6 +13902,16 @@ - (NSColor *)minimalTabStyleBackgroundColor {
     return self.currentSession.effectiveUnprocessedBackgroundColor;
 }
 
+- (NSAppearance *)sheetAppearance {
+    BOOL isDark;
+    if ((iTermPreferencesTabStyle)[iTermPreferences intForKey:kPreferenceKeyTabStyle] == TAB_STYLE_MINIMAL) {
+        isDark = self.minimalTabStyleBackgroundColor.isDark;
+    } else {
+        isDark = [self.window.effectiveAppearance bestMatchFromAppearancesWithNames:@[NSAppearanceNameDarkAqua, NSAppearanceNameAqua]] == NSAppearanceNameDarkAqua;
+    }
+    return [NSAppearance appearanceNamed:isDark ? NSAppearanceNameDarkAqua : NSAppearanceNameAqua];
+}
+
 #pragma mark - iTermBroadcastInputHelperDelegate
 
 - (NSArray<NSString *> *)broadcastInputHelperSessionsInCurrentTab:(iTermBroadcastInputHelper *)helper
diff --git a/sources/TerminalView/iTermCreateTabGroupViewController.swift b/sources/TerminalView/iTermCreateTabGroupViewController.swift
new file mode 100644
index 0000000000..151603409d
--- /dev/null
+++ b/sources/TerminalView/iTermCreateTabGroupViewController.swift
@@ -0,0 +1,354 @@
+import Cocoa
+
+@objc class iTermCreateTabGroupViewController: NSViewController {
+    var completion: ((String, NSColor)?) -> Void = { _ in }
+
+    private let swatchDiameter: CGFloat = 24
+    private let swatchSpacing: CGFloat = 8
+
+    private let swatchColors: [(NSColor, String)] = [
+        (NSColor(srgbRed: 0.259, green: 0.522, blue: 0.957, alpha: 1), "#4285F4"),
+        (NSColor(srgbRed: 0.612, green: 0.153, blue: 0.690, alpha: 1), "#9C27B0"),
+        (NSColor(srgbRed: 0.000, green: 0.537, blue: 0.482, alpha: 1), "#00897B"),
+        (NSColor(srgbRed: 0.902, green: 0.318, blue: 0.000, alpha: 1), "#E65100"),
+        (NSColor(srgbRed: 0.961, green: 0.498, blue: 0.090, alpha: 1), "#F57F17"),
+        (NSColor(srgbRed: 0.678, green: 0.078, blue: 0.341, alpha: 1), "#AD1457"),
+        (NSColor(srgbRed: 0.180, green: 0.490, blue: 0.196, alpha: 1), "#2E7D32"),
+        (NSColor(srgbRed: 0.329, green: 0.431, blue: 0.478, alpha: 1), "#546E7A"),
+        (NSColor(srgbRed: 0.776, green: 0.157, blue: 0.157, alpha: 1), "#C62828"),
+    ]
+
+    private let customColorIndex: Int
+    private var selectedColorIndex: Int = 0
+    private var nameField: NSTextField!
+    private var swatchButtons: [NSButton] = []
+    private var customColorButton: NSButton!
+    private var customColor: NSColor
+    private var doneButton: NSButton!
+    private var ownsColorPanel = false
+    private let isEditMode: Bool
+    private let isManageMode: Bool
+    private let initialName: String
+
+    // Manage-mode (popover) callbacks. Name and colour apply live as the user
+    // edits; the action closures run the corresponding group operation. All are
+    // ignored in the create/edit sheet, which commits via `completion` instead.
+    var onNameChange: ((String) -> Void)?
+    var onColorChange: ((NSColor) -> Void)?
+    var onNewTabInGroup: (() -> Void)?
+    var onUngroup: (() -> Void)?
+    var onCloseGroup: (() -> Void)?
+
+    init(initialColor: NSColor? = nil, initialName: String = "", editMode: Bool = false, manageMode: Bool = false) {
+        customColorIndex = swatchColors.count
+        customColor = NSColor(srgbRed: 0.5, green: 0.5, blue: 0.5, alpha: 1)
+        isEditMode = editMode
+        isManageMode = manageMode
+        self.initialName = initialName
+        super.init(nibName: nil, bundle: nil)
+        guard let c = initialColor?.usingColorSpace(.sRGB) else { return }
+        let matchIndex = swatchColors.enumerated().first { _, pair in
+            guard let s = pair.0.usingColorSpace(.sRGB) else { return false }
+            return abs(s.redComponent - c.redComponent) < 0.01
+                && abs(s.greenComponent - c.greenComponent) < 0.01
+                && abs(s.blueComponent - c.blueComponent) < 0.01
+        }?.offset
+        if let idx = matchIndex {
+            selectedColorIndex = idx
+        } else {
+            customColor = c
+            selectedColorIndex = customColorIndex
+        }
+    }
+
+    required init?(coder: NSCoder) {
+        customColorIndex = swatchColors.count
+        customColor = NSColor(srgbRed: 0.5, green: 0.5, blue: 0.5, alpha: 1)
+        isEditMode = false
+        isManageMode = false
+        initialName = ""
+        super.init(coder: coder)
+    }
+
+    deinit {
+        dismissColorPanel()
+    }
+
+    override func loadView() {
+        if isManageMode {
+            loadManageView()
+            return
+        }
+        let container = NSView(frame: NSRect(x: 0, y: 0, width: 340, height: 180))
+        self.view = container
+
+        let titleLabel = NSTextField(labelWithString: isEditMode ? "Edit Tab Group" : "Create Tab Group")
+        titleLabel.font = NSFont.boldSystemFont(ofSize: 13)
+        titleLabel.translatesAutoresizingMaskIntoConstraints = false
+        container.addSubview(titleLabel)
+
+        let nameLabel = NSTextField(labelWithString: "Name")
+        nameLabel.translatesAutoresizingMaskIntoConstraints = false
+        container.addSubview(nameLabel)
+
+        nameField = NSTextField()
+        nameField.placeholderString = "Name this group (optional)"
+        nameField.stringValue = initialName
+        nameField.translatesAutoresizingMaskIntoConstraints = false
+        nameField.delegate = self
+        container.addSubview(nameField)
+
+        let swatchRow = buildSwatchRow()
+        swatchRow.translatesAutoresizingMaskIntoConstraints = false
+        container.addSubview(swatchRow)
+
+        let cancelButton = NSButton(title: "Cancel", target: self, action: #selector(cancelClicked(_:)))
+        cancelButton.translatesAutoresizingMaskIntoConstraints = false
+        container.addSubview(cancelButton)
+
+        doneButton = NSButton(title: isEditMode ? "Save" : "Done", target: self, action: #selector(doneClicked(_:)))
+        doneButton.bezelStyle = .rounded
+        doneButton.keyEquivalent = "\r"
+        doneButton.isEnabled = true
+        doneButton.translatesAutoresizingMaskIntoConstraints = false
+        container.addSubview(doneButton)
+
+        let swatchRowWidth = CGFloat(customColorIndex) * swatchDiameter
+            + CGFloat(customColorIndex - 1) * swatchSpacing
+            + swatchSpacing + swatchDiameter
+
+        NSLayoutConstraint.activate([
+            titleLabel.topAnchor.constraint(equalTo: container.topAnchor, constant: 20),
+            titleLabel.centerXAnchor.constraint(equalTo: container.centerXAnchor),
+
+            nameLabel.topAnchor.constraint(equalTo: titleLabel.bottomAnchor, constant: 16),
+            nameLabel.leadingAnchor.constraint(equalTo: container.leadingAnchor, constant: 20),
+
+            nameField.centerYAnchor.constraint(equalTo: nameLabel.centerYAnchor),
+            nameField.leadingAnchor.constraint(equalTo: nameLabel.trailingAnchor, constant: 8),
+            nameField.trailingAnchor.constraint(equalTo: container.trailingAnchor, constant: -20),
+
+            swatchRow.topAnchor.constraint(equalTo: nameField.bottomAnchor, constant: 14),
+            swatchRow.centerXAnchor.constraint(equalTo: container.centerXAnchor),
+            swatchRow.widthAnchor.constraint(equalToConstant: swatchRowWidth),
+            swatchRow.heightAnchor.constraint(equalToConstant: swatchDiameter),
+
+            cancelButton.topAnchor.constraint(equalTo: swatchRow.bottomAnchor, constant: 16),
+            cancelButton.trailingAnchor.constraint(equalTo: doneButton.leadingAnchor, constant: -8),
+            cancelButton.bottomAnchor.constraint(equalTo: container.bottomAnchor, constant: -16),
+
+            doneButton.topAnchor.constraint(equalTo: swatchRow.bottomAnchor, constant: 16),
+            doneButton.trailingAnchor.constraint(equalTo: container.trailingAnchor, constant: -20),
+            doneButton.bottomAnchor.constraint(equalTo: container.bottomAnchor, constant: -16),
+        ])
+
+        updateSwatchSelection()
+        customColorButton.layer?.backgroundColor = customColor.cgColor
+    }
+
+    // Chrome-style management popover: name + colour swatches + group actions in
+    // a single transient surface. Name and colour apply live; actions invoke the
+    // corresponding closure (the presenter closes the popover).
+    private func loadManageView() {
+        let padding: CGFloat = 14
+        let swatchRowWidth = CGFloat(customColorIndex) * swatchDiameter
+            + CGFloat(customColorIndex - 1) * swatchSpacing
+            + swatchSpacing + swatchDiameter
+        let contentWidth = swatchRowWidth
+
+        nameField = NSTextField()
+        nameField.placeholderString = "Name this group (optional)"
+        nameField.stringValue = initialName
+        nameField.delegate = self
+        nameField.translatesAutoresizingMaskIntoConstraints = false
+
+        let swatchRow = buildSwatchRow()
+        swatchRow.translatesAutoresizingMaskIntoConstraints = false
+
+        let newTabButton = makeActionButton(title: "New tab in group",
+                                             symbol: "plus.square.on.square",
+                                             action: #selector(newTabInGroupClicked(_:)))
+        let ungroupButton = makeActionButton(title: "Ungroup",
+                                             symbol: "rectangle.dashed",
+                                             action: #selector(ungroupClicked(_:)))
+        let closeGroupButton = makeActionButton(title: "Close group",
+                                                symbol: "xmark.square",
+                                                action: #selector(closeGroupClicked(_:)))
+
+        let topSeparator = makeSeparator()
+
+        let stack = NSStackView(views: [
+            nameField,
+            swatchRow,
+            topSeparator,
+            newTabButton,
+            ungroupButton,
+            closeGroupButton,
+        ])
+        stack.orientation = .vertical
+        stack.alignment = .leading
+        stack.spacing = 8
+        stack.setCustomSpacing(12, after: swatchRow)
+        stack.translatesAutoresizingMaskIntoConstraints = false
+
+        let container = NSView()
+        self.view = container
+        container.addSubview(stack)
+
+        NSLayoutConstraint.activate([
+            stack.topAnchor.constraint(equalTo: container.topAnchor, constant: padding),
+            stack.leadingAnchor.constraint(equalTo: container.leadingAnchor, constant: padding),
+            stack.trailingAnchor.constraint(equalTo: container.trailingAnchor, constant: -padding),
+            stack.bottomAnchor.constraint(equalTo: container.bottomAnchor, constant: -padding),
+
+            nameField.widthAnchor.constraint(equalToConstant: contentWidth),
+            swatchRow.widthAnchor.constraint(equalToConstant: swatchRowWidth),
+            swatchRow.heightAnchor.constraint(equalToConstant: swatchDiameter),
+            topSeparator.widthAnchor.constraint(equalToConstant: contentWidth),
+        ])
+
+        updateSwatchSelection()
+        customColorButton.layer?.backgroundColor = customColor.cgColor
+        container.layoutSubtreeIfNeeded()
+        preferredContentSize = container.fittingSize
+    }
+
+    private func makeActionButton(title: String, symbol: String, action: Selector) -> NSButton {
+        let button = NSButton(title: " \(title)", target: self, action: action)
+        button.isBordered = false
+        button.bezelStyle = .regularSquare
+        button.alignment = .left
+        button.imagePosition = .imageLeading
+        button.contentTintColor = .labelColor
+        button.image = NSImage(systemSymbolName: symbol, accessibilityDescription: title)
+        button.translatesAutoresizingMaskIntoConstraints = false
+        return button
+    }
+
+    private func makeSeparator() -> NSBox {
+        let box = NSBox()
+        box.boxType = .separator
+        box.translatesAutoresizingMaskIntoConstraints = false
+        return box
+    }
+
+    @objc private func newTabInGroupClicked(_ sender: Any?) { onNewTabInGroup?() }
+    @objc private func ungroupClicked(_ sender: Any?) { onUngroup?() }
+    @objc private func closeGroupClicked(_ sender: Any?) { onCloseGroup?() }
+
+    private func notifyColorChange() {
+        guard isManageMode else { return }
+        onColorChange?(selectedColorIndex == customColorIndex ? customColor : swatchColors[selectedColorIndex].0)
+    }
+
+    private func buildSwatchRow() -> NSView {
+        let container = NSView()
+        for (index, (color, _)) in swatchColors.enumerated() {
+            let button = NSButton()
+            button.title = ""
+            button.isBordered = false
+            button.wantsLayer = true
+            button.layer?.cornerRadius = swatchDiameter / 2
+            button.layer?.backgroundColor = color.cgColor
+            button.tag = index
+            button.target = self
+            button.action = #selector(swatchClicked(_:))
+            button.frame = NSRect(x: CGFloat(index) * (swatchDiameter + swatchSpacing),
+                                  y: 0,
+                                  width: swatchDiameter,
+                                  height: swatchDiameter)
+            container.addSubview(button)
+            swatchButtons.append(button)
+        }
+
+        customColorButton = NSButton()
+        customColorButton.title = ""
+        customColorButton.isBordered = false
+        customColorButton.wantsLayer = true
+        customColorButton.layer?.cornerRadius = swatchDiameter / 2
+        customColorButton.layer?.backgroundColor = customColor.cgColor
+        if let icon = NSImage(systemSymbolName: "eyedropper", accessibilityDescription: "Custom colour") {
+            customColorButton.image = icon
+            customColorButton.imagePosition = .imageOnly
+            customColorButton.contentTintColor = NSColor.white.withAlphaComponent(0.85)
+        }
+        customColorButton.tag = customColorIndex
+        customColorButton.target = self
+        customColorButton.action = #selector(customColorActivated(_:))
+        customColorButton.frame = NSRect(x: CGFloat(customColorIndex) * (swatchDiameter + swatchSpacing),
+                                         y: 0,
+                                         width: swatchDiameter,
+                                         height: swatchDiameter)
+        container.addSubview(customColorButton)
+        return container
+    }
+
+    private func updateSwatchSelection() {
+        for (index, button) in swatchButtons.enumerated() {
+            button.layer?.borderWidth = index == selectedColorIndex ? 2.5 : 0
+            button.layer?.borderColor = NSColor.white.cgColor
+        }
+        customColorButton.layer?.borderWidth = selectedColorIndex == customColorIndex ? 2.5 : 0
+        customColorButton.layer?.borderColor = NSColor.white.cgColor
+    }
+
+    @objc private func swatchClicked(_ sender: NSButton) {
+        selectedColorIndex = sender.tag
+        updateSwatchSelection()
+        notifyColorChange()
+    }
+
+    @objc private func customColorActivated(_ sender: NSButton) {
+        selectedColorIndex = customColorIndex
+        updateSwatchSelection()
+        notifyColorChange()
+        let panel = NSColorPanel.shared
+        panel.color = customColor
+        panel.setTarget(self)
+        panel.setAction(#selector(colorPanelColorChanged(_:)))
+        ownsColorPanel = true
+        panel.orderFront(nil)
+    }
+
+    @objc private func colorPanelColorChanged(_ sender: NSColorPanel) {
+        customColor = sender.color
+        customColorButton.layer?.backgroundColor = customColor.cgColor
+        if selectedColorIndex == customColorIndex {
+            updateSwatchSelection()
+            notifyColorChange()
+        }
+    }
+
+    @objc private func cancelClicked(_ sender: Any?) {
+        dismissColorPanel()
+        completion(nil)
+    }
+
+    @objc private func doneClicked(_ sender: Any?) {
+        dismissColorPanel()
+        let name = nameField.stringValue.trimmingCharacters(in: .whitespaces)
+        let color: NSColor
+        if selectedColorIndex == customColorIndex {
+            color = customColor
+        } else {
+            color = swatchColors[selectedColorIndex].0
+        }
+        completion((name, color))
+    }
+
+    private func dismissColorPanel() {
+        guard ownsColorPanel else { return }
+        ownsColorPanel = false
+        let panel = NSColorPanel.shared
+        panel.setTarget(nil)
+        panel.setAction(nil)
+        panel.orderOut(nil)
+    }
+}
+
+extension iTermCreateTabGroupViewController: NSTextFieldDelegate {
+    func controlTextDidChange(_ obj: Notification) {
+        guard isManageMode else { return }
+        onNameChange?(nameField.stringValue.trimmingCharacters(in: .whitespaces))
+    }
+}
diff --git a/sources/TerminalView/iTermRootTerminalView.h b/sources/TerminalView/iTermRootTerminalView.h
index 757b35ecb5..107fcc2662 100644
--- a/sources/TerminalView/iTermRootTerminalView.h
+++ b/sources/TerminalView/iTermRootTerminalView.h
@@ -14,13 +14,15 @@
 @class iTermRootTerminalView;
 @class iTermStatusBarViewController;
 @protocol iTermSwipeHandler;
-@class iTermTabBarControlView;
+#import "iTermTabBarControlView.h"
+#import "PTYTabView.h"
 @protocol iTermTabBarControlViewDelegate;
 @class iTermToolbeltView;
 @protocol iTermToolbeltViewDelegate;
 @protocol PSMTabBarControlDelegate;
 @protocol PSMPUAFontProvider;
-@class PTYTabView;
+
+NS_ASSUME_NONNULL_BEGIN
 
 @protocol iTermRootTerminalViewDelegate<iTermTabBarControlViewDelegate, iTermSwipeHandler>
 - (void)repositionWidgets;
@@ -48,10 +50,10 @@
 - (NSColor *)rootTerminalViewTabBarBackgroundColorIgnoringTabColor:(BOOL)ignoreTabColor;
 - (BOOL)rootTerminalViewWindowNumberLabelShouldBeVisible;
 - (BOOL)rootTerminalViewShouldDrawWindowTitleInPlaceOfTabBar;
-- (NSImage *)rootTerminalViewCurrentTabIcon;
+- (nullable NSImage *)rootTerminalViewCurrentTabIcon;
 - (BOOL)rootTerminalViewShouldDrawStoplightButtons;
 - (BOOL)rootTerminalViewShouldRevealStandardWindowButtons;
-- (iTermStatusBarViewController *)rootTerminalViewSharedStatusBarViewController;
+- (nullable iTermStatusBarViewController *)rootTerminalViewSharedStatusBarViewController;
 
 // Returns YES when the tab bar is a titlebar accessory in fullscreen AND the window
 // uses NSWindowStyleMaskFullSizeContentView, meaning the content view extends under
@@ -69,7 +71,7 @@
 - (NSString *)rootTerminalViewWindowSizeViewDetailString;
 - (void)rootTerminalViewWillLayoutSubviews;
 - (void)rootTerminalViewDidLayoutSubviews;
-- (NSString *)rootTerminalViewCurrentTabSubtitle;
+- (nullable NSString *)rootTerminalViewCurrentTabSubtitle;
 - (id<PSMPUAFontProvider>)rootTerminalViewPUAFontProvider;
 @end
 
@@ -92,7 +94,7 @@ extern const NSInteger iTermRootTerminalViewWindowNumberLabelWidth;
 // Gray line dividing tab/title bar from content. Will be nil if a division
 // view isn't needed such as for fullscreen windows or windows without a
 // title bar (e.g., top-of-screen).
-@property(nonatomic, readonly) NSView<iTermSolidColorView> *divisionView;
+@property(nonatomic, readonly, nullable) NSView<iTermSolidColorView> *divisionView;
 
 // Toolbelt view. Goes on the right side of the terminal window, if visible.
 @property(nonatomic, readonly) iTermToolbeltView *toolbelt;
@@ -114,10 +116,10 @@ extern const NSInteger iTermRootTerminalViewWindowNumberLabelWidth;
 
 @property(nonatomic) BOOL useMetal;
 @property(nonatomic, readonly) BOOL tabBarControlOnLoan NS_AVAILABLE_MAC(10_14);
-@property(nonatomic, strong, readonly) iTermStatusBarViewController *statusBarViewController;
+@property(nonatomic, strong, readonly, nullable) iTermStatusBarViewController *statusBarViewController;
 @property(nonatomic, readonly) iTermImageView *backgroundImage NS_AVAILABLE_MAC(10_14);
 // Excludes the window number
-@property(nonatomic, readonly) NSString *windowTitle;
+@property(nonatomic, readonly, nullable) NSString *windowTitle;
 
 - (instancetype)initWithFrame:(NSRect)frame
                         color:(NSColor *)color
@@ -128,8 +130,8 @@ extern const NSInteger iTermRootTerminalViewWindowNumberLabelWidth;
 - (void)updateDivisionViewAndWindowNumberLabel;
 
 // Perform a layout pass on the toolbelt, and hide/show it as needed.
-- (void)updateToolbeltFrameForWindow:(NSWindow *)thisWindow;
-- (void)updateToolbeltForWindow:(NSWindow *)thisWindow;
+- (void)updateToolbeltFrameForWindow:(nullable NSWindow *)thisWindow;
+- (void)updateToolbeltForWindow:(nullable NSWindow *)thisWindow;
 
 // TODO: Don't expose this
 - (void)constrainToolbeltWidth;
@@ -146,8 +148,8 @@ extern const NSInteger iTermRootTerminalViewWindowNumberLabelWidth;
 - (void)didChangeCompactness;
 
 - (void)windowTitleDidChangeTo:(NSString *)title;
-- (void)windowNumberDidChangeTo:(NSNumber *)number;
-- (void)setWindowTitleIcon:(NSImage *)icon;
+- (void)windowNumberDidChangeTo:(nullable NSNumber *)number;
+- (void)setWindowTitleIcon:(nullable NSImage *)icon;
 - (iTermTabBarControlView *)borrowTabBarControl NS_AVAILABLE_MAC(10_14);
 - (void)returnTabBarControlView:(iTermTabBarControlView *)tabBarControl NS_AVAILABLE_MAC(10_14);
 - (CGFloat)maximumToolbeltWidthForViewWidth:(CGFloat)viewWidth;
@@ -164,3 +166,5 @@ extern const NSInteger iTermRootTerminalViewWindowNumberLabelWidth;
 - (CGFloat)compactProxyIconWidthIncludingMargin;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/sources/TerminalView/iTermTabBarControlView.m b/sources/TerminalView/iTermTabBarControlView.m
index 8b8608df8f..8e94ae83df 100644
--- a/sources/TerminalView/iTermTabBarControlView.m
+++ b/sources/TerminalView/iTermTabBarControlView.m
@@ -287,9 +287,10 @@ - (void)setOrientation:(PSMTabBarOrientation)orientation {
 
 - (BOOL)cellAllowsTabProgressBar:(PSMTabBarCell *)cell {
     NSTabViewItem *item = (NSTabViewItem *)cell.representedObject;
-    PTYTab *tab = item.identifier;
-    if (![tab isKindOfClass:[PTYTab class]]) {
-        return YES;
+    PTYTab *tab = item.it_tab;
+    if (!tab) {
+        // Group header items have no tab and never show progress.
+        return NO;
     }
     return tab.activeSession.view.enableProgressBars;
 }
@@ -306,8 +307,8 @@ - (BOOL)cellShouldShowTabProgressBar:(PSMTabBarCell *)cell {
 
 - (NSString *)tabProgressBarColorSchemeForCell:(PSMTabBarCell *)cell {
     NSTabViewItem *item = (NSTabViewItem *)cell.representedObject;
-    PTYTab *tab = item.identifier;
-    if (![tab isKindOfClass:[PTYTab class]]) {
+    PTYTab *tab = item.it_tab;
+    if (!tab) {
         return iTermProgressBarColorSchemeDefault;
     }
     return tab.activeSession.view.progressBarColorScheme ?: iTermProgressBarColorSchemeDefault;
diff --git a/sources/TerminalView/iTermTabGroup.swift b/sources/TerminalView/iTermTabGroup.swift
new file mode 100644
index 0000000000..6dc63b8a72
--- /dev/null
+++ b/sources/TerminalView/iTermTabGroup.swift
@@ -0,0 +1,79 @@
+import Cocoa
+
+@objc class iTermTabGroup: NSObject {
+    @objc let identifier: String
+    @objc var name: String
+    @objc var color: NSColor
+    @objc var memberTabIDs: [Int]
+    @objc var isCollapsed: Bool
+    var stashedTabViewItems: [NSTabViewItem] = []
+    @objc let headerTabViewItem: NSTabViewItem
+
+    private enum CodingKey {
+        static let identifier = "identifier"
+        static let name = "name"
+        static let color = "color"
+        static let memberTabIndices = "memberTabIndices"
+        static let isCollapsed = "isCollapsed"
+    }
+
+    @objc(groupWithName:color:)
+    static func group(name: String, color: NSColor) -> iTermTabGroup {
+        return iTermTabGroup(name: name, color: color)
+    }
+
+    private static func makeHeaderItem(label: String) -> NSTabViewItem {
+        let item = NSTabViewItem()
+        item.label = label
+        item.view = NSView(frame: .zero)
+        return item
+    }
+
+    @objc init(name: String, color: NSColor) {
+        self.identifier = UUID().uuidString
+        self.name = name
+        self.color = color
+        self.memberTabIDs = []
+        self.isCollapsed = false
+        let item = iTermTabGroup.makeHeaderItem(label: name)
+        self.headerTabViewItem = item
+        super.init()
+        item.identifier = self
+    }
+
+    @objc func toDictionary(allTabs: [PTYTab]) -> [String: Any] {
+        let indices = memberTabIDs.compactMap { id -> NSNumber? in
+            guard let index = allTabs.firstIndex(where: { Int($0.uniqueId) == id }) else { return nil }
+            return NSNumber(value: index)
+        }
+        var dict: [String: Any] = [
+            CodingKey.identifier: identifier,
+            CodingKey.name: name,
+            CodingKey.memberTabIndices: indices,
+            CodingKey.isCollapsed: isCollapsed
+        ]
+        if let colorData = try? NSKeyedArchiver.archivedData(withRootObject: color, requiringSecureCoding: false) {
+            dict[CodingKey.color] = colorData
+        }
+        return dict
+    }
+
+    @objc init?(dictionary: [String: Any]) {
+        guard let identifier = dictionary[CodingKey.identifier] as? String,
+              let name = dictionary[CodingKey.name] as? String,
+              let colorData = dictionary[CodingKey.color] as? Data,
+              let color = try? NSKeyedUnarchiver.unarchivedObject(ofClass: NSColor.self, from: colorData),
+              let rawIndices = dictionary[CodingKey.memberTabIndices] as? [NSNumber] else {
+            return nil
+        }
+        self.identifier = identifier
+        self.name = name
+        self.color = color
+        self.memberTabIDs = rawIndices.map { $0.intValue }
+        self.isCollapsed = (dictionary[CodingKey.isCollapsed] as? Bool) ?? false
+        let item = iTermTabGroup.makeHeaderItem(label: name)
+        self.headerTabViewItem = item
+        super.init()
+        item.identifier = self
+    }
+}