diff --git a/.changeset/poor-ends-peel.md b/.changeset/poor-ends-peel.md
new file mode 100644
index 0000000000..c3262eaf6c
--- /dev/null
+++ b/.changeset/poor-ends-peel.md
@@ -0,0 +1,5 @@
+---
+"@rainbow-me/rainbowkit": patch
+---
+
+Made `getNonce` optional in `AuthenticationAdapter`. When the server generates the nonce alongside the SIWE message, you can now omit `getNonce` entirely—RainbowKit will skip the client-side nonce pre-fetch and call `createMessage` directly with `{ address, chainId }`. Adapters that already provide `getNonce` keep the existing behavior and continue to receive `nonce` in `createMessage` args.
diff --git a/packages/rainbowkit/src/components/RainbowKitProvider/AuthenticationContext.tsx b/packages/rainbowkit/src/components/RainbowKitProvider/AuthenticationContext.tsx
index dbc5655d83..3ef3ed8662 100644
--- a/packages/rainbowkit/src/components/RainbowKitProvider/AuthenticationContext.tsx
+++ b/packages/rainbowkit/src/components/RainbowKitProvider/AuthenticationContext.tsx
@@ -14,17 +14,33 @@ export type AuthenticationStatus =
   | 'unauthenticated'
   | 'authenticated';
 
-export interface AuthenticationAdapter<Message> {
-  getNonce: () => Promise<string>;
-  createMessage: (args: {
-    nonce: string;
-    address: Address;
-    chainId: number;
-  }) => Promise<Message> | Message;
+interface AuthenticationAdapterBase<Message> {
   verify: (args: { message: Message; signature: string }) => Promise<boolean>;
   signOut: () => Promise<void>;
 }
 
+// When `getNonce` is omitted, RainbowKit skips client-side nonce pre-fetching
+// and calls `createMessage` directly with `{ address, chainId }`
+export type AuthenticationAdapter<Message> =
+  AuthenticationAdapterBase<Message> &
+    (
+      | {
+          getNonce: () => Promise<string>;
+          createMessage: (args: {
+            nonce: string;
+            address: Address;
+            chainId: number;
+          }) => Promise<Message> | Message;
+        }
+      | {
+          getNonce?: undefined;
+          createMessage: (args: {
+            address: Address;
+            chainId: number;
+          }) => Promise<Message> | Message;
+        }
+    );
+
 export interface AuthenticationConfig<Message> {
   adapter: AuthenticationAdapter<Message>;
   status: AuthenticationStatus;
diff --git a/packages/rainbowkit/src/components/SignIn/SignIn.test.tsx b/packages/rainbowkit/src/components/SignIn/SignIn.test.tsx
index 19cd92e609..0a5ba62ca5 100644
--- a/packages/rainbowkit/src/components/SignIn/SignIn.test.tsx
+++ b/packages/rainbowkit/src/components/SignIn/SignIn.test.tsx
@@ -32,19 +32,34 @@ const address = '0x0000000000000000000000000000000000000001' as Address;
 
 function renderSignIn({
   createMessage,
+  getNonce = async () => 'nonce',
 }: {
   createMessage: (args: {
-    nonce: string;
+    nonce?: string;
     address: Address;
     chainId: number;
   }) => string | Promise<string>;
+  // Pass `null` to omit `getNonce` entirely (server-side message creation).
+  getNonce?: (() => Promise<string>) | null;
 }) {
-  const adapter = createAuthenticationAdapter<string>({
-    createMessage,
-    getNonce: async () => 'nonce',
-    signOut: async () => {},
-    verify: async () => true,
-  });
+  const adapter = createAuthenticationAdapter<string>(
+    getNonce === null
+      ? {
+          createMessage,
+          signOut: async () => {},
+          verify: async () => true,
+        }
+      : {
+          createMessage: createMessage as (args: {
+            nonce: string;
+            address: Address;
+            chainId: number;
+          }) => string | Promise<string>,
+          getNonce,
+          signOut: async () => {},
+          verify: async () => true,
+        },
+  );
 
   return render(
     <RainbowKitAuthenticationProvider
@@ -78,6 +93,11 @@ describe('SignIn', () => {
     fireEvent.click(button);
 
     expect(createMessage).toHaveBeenCalledOnce();
+    expect(createMessage).toHaveBeenCalledWith({
+      address,
+      chainId: 1,
+      nonce: 'nonce',
+    });
     await waitFor(() =>
       expect(wagmiMocks.signMessageAsync).toHaveBeenCalledWith({
         message: 'message',
@@ -142,4 +162,30 @@ describe('SignIn', () => {
 
     expect(createMessage).toHaveBeenCalledTimes(2);
   });
+
+  it('enables sign-in immediately when getNonce is omitted', async () => {
+    const createMessage = vi.fn(() => 'message');
+    wagmiMocks.signMessageAsync.mockReturnValue(new Promise(() => {}));
+
+    renderSignIn({ createMessage, getNonce: null });
+
+    const button = await screen.findByTestId('rk-auth-message-button');
+    expect(button).toHaveTextContent('Sign message');
+    expect(button).not.toBeDisabled();
+
+    fireEvent.click(button);
+
+    expect(createMessage).toHaveBeenCalledOnce();
+    // No nonce should be passed to createMessage when getNonce is omitted.
+    expect(createMessage).toHaveBeenCalledWith({
+      address,
+      chainId: 1,
+    });
+
+    await waitFor(() =>
+      expect(wagmiMocks.signMessageAsync).toHaveBeenCalledWith({
+        message: 'message',
+      }),
+    );
+  });
 });
diff --git a/packages/rainbowkit/src/components/SignIn/SignIn.tsx b/packages/rainbowkit/src/components/SignIn/SignIn.tsx
index 993ced248a..ce82eef184 100644
--- a/packages/rainbowkit/src/components/SignIn/SignIn.tsx
+++ b/packages/rainbowkit/src/components/SignIn/SignIn.tsx
@@ -30,6 +30,8 @@ export function SignIn({
   const authAdapter = useAuthenticationAdapter();
 
   const getNonce = useCallback(async () => {
+    if (!authAdapter.getNonce) return;
+
     try {
       const nonce = await authAdapter.getNonce();
       setState((x) => ({ ...x, nonce }));
@@ -62,9 +64,10 @@ export function SignIn({
       const chainId = activeChain?.id;
       const { nonce } = state;
 
-      if (!address || !chainId || !nonce) {
-        return;
-      }
+      if (!address || !chainId) return;
+
+      // Block when the adapter expects a pre-fetched nonce that hasn't arrived.
+      if (authAdapter.getNonce && !nonce) return;
 
       setState((x) => ({
         ...x,
@@ -73,11 +76,18 @@ export function SignIn({
 
       let message: Awaited<ReturnType<typeof authAdapter.createMessage>>;
       try {
-        const messageResult = authAdapter.createMessage({
-          address,
-          chainId,
-          nonce,
-        });
+        let messageResult: ReturnType<typeof authAdapter.createMessage>;
+        if (authAdapter.getNonce) {
+          // This isn't reachable in practice, but for type safety.
+          if (!nonce) return;
+          messageResult = authAdapter.createMessage({
+            address,
+            chainId,
+            nonce,
+          });
+        } else {
+          messageResult = authAdapter.createMessage({ address, chainId });
+        }
 
         if (messageResult instanceof Promise) {
           setState((x) => ({ ...x, status: 'creatingMessage' }));
@@ -223,13 +233,14 @@ export function SignIn({
         >
           <ActionButton
             disabled={
-              !state.nonce ||
+              (authAdapter.getNonce && !state.nonce) ||
               status === 'creatingMessage' ||
               status === 'signing' ||
               status === 'verifying'
             }
             label={
-              !state.nonce || status === 'creatingMessage'
+              (authAdapter.getNonce && !state.nonce) ||
+              status === 'creatingMessage'
                 ? i18n.t('sign_in.message.preparing')
                 : status === 'signing'
                   ? i18n.t('sign_in.signature.waiting')
diff --git a/site/data/en-US/docs/custom-authentication.mdx b/site/data/en-US/docs/custom-authentication.mdx
index 0c7f0e4547..8d7da505a7 100644
--- a/site/data/en-US/docs/custom-authentication.mdx
+++ b/site/data/en-US/docs/custom-authentication.mdx
@@ -57,7 +57,10 @@ const authenticationAdapter = createAuthenticationAdapter({
 
 `createMessage` also supports returning a `Promise`, allowing you to construct [EIP-4361](https://eips.ethereum.org/EIPS/eip-4361) messages on the server. For stricter security, the server endpoint should derive or validate security-critical fields like `domain`, `nonce`, and `issued-at` timestamps instead of trusting client-provided values. See [SIWE documentation](https://docs.siwe.xyz/security-considerations#server-side-message-generation) for more details.
 
+When the server generates the nonce alongside the message, you can omit `getNonce`. RainbowKit will skip nonce pre-fetching and call `createMessage` directly with `{ address, chainId }`:
+
 ```tsx
+const authenticationAdapter = createAuthenticationAdapter({
   createMessage: async ({ address, chainId }) => {
     const response = await fetch('/api/siwe/message', {
       method: 'POST',
@@ -71,8 +74,19 @@ const authenticationAdapter = createAuthenticationAdapter({
 
     return await response.text();
   },
+
+  verify: async ({ message, signature }) => {
+    /* ... */
+  },
+
+  signOut: async () => {
+    /* ... */
+  },
+});
 ```
 
+If you still want the client to fetch a nonce separately (for example, to keep the existing `/api/nonce` endpoint), keep `getNonce` and continue to receive `nonce` in `createMessage` args.
+
 #### Providing the authentication state
 
 Assuming your application is already managing the authentication lifecycle in some way, you can pass the current authentication status along with your custom adapter to `RainbowKitAuthenticationProvider`, wrapping your existing `RainbowKitProvider`.