Cursor flicker in Neovim

[alewis001]

Hi,

I'm not sure if this is an issue in tmux, Neovim, Ghostty or has already been reported and I've done a poor job of trying to find it (I have tried) so, I'm starting here as the behaviour I'm seeing changed between tmux 3.6 and 3.7.

When I open Neovim, I see the cursor flicker all over the terminal window until it settles in it's normal position at the beginning of the buffer. The flickering doesn't happen outside tmux (i.e. just neovim in ghostty), if that helps narrow it down.

Versions:

• tmux 3.7b
• NVIM v0.12.4
• Ghostty 1.3.1
• MacOS Tahoe 26.5.2 (25F84)

Sorry for the large terminal window in the recording but it makes the flickering more visible:

Screen.Recording.2026-07-21.at.17.26.04.mov

[nicm]

Does this still happen if you build tmux from master?

[nicm]

macOS master has extra debugging code because there is a bug that only triggers on macOS so it might be slower.

[alewis001]

macOS master has extra debugging code because there is a bug that only triggers on macOS so it might be slower.

Ah, got ya. Thanks

[halfmu]

I also had a similar issue. Saw cursor flickering in neovim after upgrading to 3.7b, so switched to tmux master which resolved the issue. But every time when I use fzflua in neovim (invoking any picker in a floating window), I saw everything crawling, and cpu spiked significantly for iTerm2. After sample the iTerm2 process, I saw hot path of the following which appeared to be repeatedly processing terminal color-reset escape sequences according to codex:

terminalResetColor
-> screenResetColorWithColorMapKey
-> setSessionSpecificProfileValues

I was able to workaround that by disabling terminal cursor-color support (Cr and Cs) in tmux with set-option -ga terminal-overrides ',xterm-256color:Cr@:Cs@'.

[GNOMES]

This could be a red herring, but I may have pinned this issue down to a Neovim config setting + Tmux 3.7c.

Using either Ghostty or stock Mac Terminal + tmux kill-server; tmux -vv new, I tried nvim --clean, and nvim -U NONE -i NONE + opening a random file (I used my .bashrc) - I was not able to trigger the issue.

I next disabled all lines in my config, adding them back one by one.

I currently use:vim.o.cmdheight = 0 and vim.o.laststatus = 0

With both disabled, I don't encounter the flickering issue. If I have either or both enabled, and hold J/K in .bashrc, eventually I get this flickering issue similar to @alewis001.

I am not using Snacks. For me it first looks like the cursor is trying to move along the last character of each row (which is odd as I am in the first column). Continuing to move up/down causes more flickering in various places like in the gif.

When issue is happening scrolling is very slow. Performance is back to normal after it stops until re-triggered.

@halfmu settings had no effect for me.

I experience no problems outside of Tmux with both vim.o.cmdheight = 0 and vim.o.laststatus = 0 enabled using both Ghostty and Mac Terminal.

Due to environment variables and other information in the generated -vv log file, I don't feel comfortable posting full log from this particular computer. The generated log also grows very fast to 100k + lines. Not sure if that's abnormal.

@nicm are there any debug messages or patterns you would look for when this kind of artifacting/cursor behavior happens? I can raise an issue with relevant messages if I find them.

[nicm]

If you can reproduce with master then open an issue please with logs.

[GNOMES]

So building from master (commit c1f947a), and simply running ./tmux without -vv, I coud not replicate the issue.

When I do add the -vv the issue is reproducible

I will try sanitizing a log later today.

[luisdavim]

I haven't tried building from master but on 3.7c I can reproduce this both on neovim as well as outside, with mouse scrolling through output from something like delta (the diff viewer).

[nicm]

I think I fixed this recently in master.

[luisdavim]

I've reinstalled using brew install --HEAD tmux I have:

$  tmux -V
tmux next-3.8

$ brew upgrade --fetch-HEAD tmux
==> Downloading Homebrew API data
✔︎ JSON API packages.arm64_tahoe.jws.json            Downloaded   15.5MB/ 15.5MB
Warning: tmux HEAD-578e07f already installed

And I still see the issue.

[luisdavim]

update, I can also reproduce the issue without tmux, this might be a ghostty thing, I'll also try other terminals.