diff --git a/packages/controller/src/controller.ts b/packages/controller/src/controller.ts
index b8930c180..f9b1727e0 100644
--- a/packages/controller/src/controller.ts
+++ b/packages/controller/src/controller.ts
@@ -789,6 +789,7 @@ export default class ControllerProvider extends BaseProvider {
     const iframe = new KeychainIFrame({
       ...this.options,
       rpcUrl: this.rpcUrl(),
+      chainId: this.selectedChain,
       onClose: () => {
         this.keychain?.reset?.();
       },
diff --git a/packages/controller/src/iframe/keychain.ts b/packages/controller/src/iframe/keychain.ts
index ef27d906f..1733d8a71 100644
--- a/packages/controller/src/iframe/keychain.ts
+++ b/packages/controller/src/iframe/keychain.ts
@@ -6,6 +6,7 @@ import { IFrame, IFrameOptions } from "./base";
 type KeychainIframeOptions = IFrameOptions<Keychain> &
   KeychainOptions & {
     version?: string;
+    chainId?: string;
     ref?: string;
     refGroup?: string;
     needsSessionCreation?: boolean;
@@ -31,6 +32,7 @@ export class KeychainIFrame extends IFrame<Keychain> {
     preset,
     shouldOverridePresetPolicies,
     rpcUrl,
+    chainId,
     ref,
     refGroup,
     needsSessionCreation,
@@ -77,6 +79,10 @@ export class KeychainIFrame extends IFrame<Keychain> {
       _url.searchParams.set("rpc_url", encodeURIComponent(rpcUrl));
     }
 
+    if (chainId) {
+      _url.searchParams.set("chain_id", chainId);
+    }
+
     if (ref) {
       _url.searchParams.set("ref", encodeURIComponent(ref));
     }
diff --git a/packages/controller/src/node/provider.ts b/packages/controller/src/node/provider.ts
index 8f5964312..a6a410329 100644
--- a/packages/controller/src/node/provider.ts
+++ b/packages/controller/src/node/provider.ts
@@ -146,7 +146,7 @@ export default class SessionProvider extends BaseProvider {
       redirectUri,
     )}&redirect_query_name=startapp&policies=${encodeURIComponent(
       JSON.stringify(this._policies),
-    )}&rpc_url=${encodeURIComponent(this._rpcUrl)}`;
+    )}&rpc_url=${encodeURIComponent(this._rpcUrl)}&chain_id=${encodeURIComponent(this._chainId)}`;
 
     this._backend.openLink(url);
 
diff --git a/packages/controller/src/session/provider.ts b/packages/controller/src/session/provider.ts
index 31ebba76a..8915192eb 100644
--- a/packages/controller/src/session/provider.ts
+++ b/packages/controller/src/session/provider.ts
@@ -295,7 +295,8 @@ export default class SessionProvider extends BaseProvider {
           `/session?public_key=${this._publicKey}` +
           `&redirect_uri=${this._redirectUrl}` +
           `&redirect_query_name=startapp` +
-          `&rpc_url=${this._rpcUrl}`;
+          `&rpc_url=${this._rpcUrl}` +
+          `&chain_id=${this._chainId}`;
 
         if (this._preset) {
           url += `&preset=${encodeURIComponent(this._preset)}`;
diff --git a/packages/controller/src/telegram/provider.ts b/packages/controller/src/telegram/provider.ts
index e24832b13..7a64290ca 100644
--- a/packages/controller/src/telegram/provider.ts
+++ b/packages/controller/src/telegram/provider.ts
@@ -82,7 +82,7 @@ export default class TelegramProvider extends BaseProvider {
       this._tmaUrl
     }&redirect_query_name=startapp&policies=${JSON.stringify(
       this._policies,
-    )}&rpc_url=${this._rpcUrl}`;
+    )}&rpc_url=${this._rpcUrl}&chain_id=${this._chainId}`;
 
     localStorage.setItem("lastUsedConnector", this.id);
     openLink(url);
diff --git a/packages/keychain/src/hooks/connection.test.ts b/packages/keychain/src/hooks/connection.test.ts
index b79d5a166..151de76b3 100644
--- a/packages/keychain/src/hooks/connection.test.ts
+++ b/packages/keychain/src/hooks/connection.test.ts
@@ -396,44 +396,59 @@ describe("URL rpc_url priority over stored controller rpcUrl", () => {
   });
 
   describe("Controller disconnect on chain mismatch", () => {
-    it("should disconnect controller when URL rpc_url differs from stored controller", () => {
-      const urlRpcUrl = "https://api.cartridge.gg/x/starknet/mainnet";
+    it("should disconnect controller when chain IDs differ", () => {
+      // Controller is on sepolia (0x534e5f534550), URL requests mainnet
+      const controllerChainId = mockController.chainId();
+      const urlChainId = "0x534e5f4d41494e"; // SN_MAIN
 
-      // Simulate the effect logic: URL rpc_url differs from controller's rpcUrl
-      const controllerRpcUrl = mockController.rpcUrl();
-      expect(controllerRpcUrl).not.toBe(urlRpcUrl);
+      expect(controllerChainId).not.toBe(urlChainId);
 
-      // The effect should trigger disconnect when rpcUrls don't match
+      // The effect should trigger disconnect when chain IDs don't match
       const shouldDisconnect =
-        mockController && urlRpcUrl && controllerRpcUrl !== urlRpcUrl;
+        mockController && urlChainId && controllerChainId !== urlChainId;
       expect(shouldDisconnect).toBeTruthy();
     });
 
-    it("should NOT disconnect controller when URL rpc_url matches stored controller", () => {
-      const urlRpcUrl = "https://rpc.sepolia.example.com";
-      const controllerRpcUrl = mockController.rpcUrl();
+    it("should NOT disconnect controller when chain IDs match", () => {
+      // Same chain, potentially different RPC endpoints
+      const controllerChainId = mockController.chainId();
+      const urlChainId = "0x534e5f534550"; // SN_SEPOLIA (matches mock)
 
-      // URLs match - no disconnect should happen
-      expect(controllerRpcUrl).toBe(urlRpcUrl);
+      expect(controllerChainId).toBe(urlChainId);
 
-      const shouldDisconnect = controllerRpcUrl !== urlRpcUrl;
+      const shouldDisconnect = controllerChainId !== urlChainId;
       expect(shouldDisconnect).toBe(false);
     });
 
-    it("should NOT disconnect controller when no URL rpc_url is provided", () => {
-      const urlRpcUrl = null;
+    it("should NOT disconnect when chain IDs match despite different RPC URLs", () => {
+      // Both on sepolia but using different RPC endpoints
+      const controllerChainId = mockController.chainId(); // 0x534e5f534550
+      const urlChainId = "0x534e5f534550"; // SN_SEPOLIA
+
+      // RPC URLs differ, but chain IDs match — no disconnect
+      const controllerRpcUrl = mockController.rpcUrl(); // sepolia.example.com
+      const urlRpcUrl = "https://other-provider.com/sepolia";
+      expect(controllerRpcUrl).not.toBe(urlRpcUrl);
+      expect(controllerChainId).toBe(urlChainId);
 
-      // No urlRpcUrl - the effect guard returns early
-      const shouldDisconnect = urlRpcUrl !== null;
+      const shouldDisconnect = controllerChainId !== urlChainId;
       expect(shouldDisconnect).toBe(false);
     });
 
+    it("should NOT disconnect controller when chainId is undefined", () => {
+      const chainId = undefined;
+
+      // No chainId - the effect guard returns early
+      const shouldDisconnect = mockController && chainId;
+      expect(shouldDisconnect).toBeFalsy();
+    });
+
     it("should NOT disconnect controller when controller is not set", () => {
       const controller = undefined;
-      const urlRpcUrl = "https://api.cartridge.gg/x/starknet/mainnet";
+      const chainId = "0x534e5f4d41494e";
 
       // No controller - the effect guard returns early
-      const shouldDisconnect = controller && urlRpcUrl;
+      const shouldDisconnect = controller && chainId;
       expect(shouldDisconnect).toBeFalsy();
     });
   });
diff --git a/packages/keychain/src/hooks/connection.ts b/packages/keychain/src/hooks/connection.ts
index c5a557a18..99487c61c 100644
--- a/packages/keychain/src/hooks/connection.ts
+++ b/packages/keychain/src/hooks/connection.ts
@@ -244,7 +244,12 @@ export function useConnectionValue() {
     ...defaultTheme,
   });
   const [controller, setController] = useState(window.controller);
-  const [chainId, setChainId] = useState<string>();
+  const [chainId, setChainId] = useState<string | undefined>(() =>
+    typeof window !== "undefined"
+      ? (new URLSearchParams(window.location.search).get("chain_id") ??
+        undefined)
+      : undefined,
+  );
   const [controllerVersion, setControllerVersion] = useState<SemVer>();
   const connectionStateRef = useRef<HeadlessConnectionState>({
     origin,
@@ -277,20 +282,23 @@ export function useConnectionValue() {
     }
   }, [controller, setRpcUrl, urlRpcUrl]);
 
-  // When URL provides an rpc_url that differs from the controller's, log the user
-  // out so they re-authenticate on the correct chain. The account may not be deployed
-  // on the target chain, so we can't simply recreate the controller.
+  // When the requested chain differs from the controller's, log the user out so
+  // they re-authenticate on the correct chain. Compares chain IDs (semantic
+  // equality) rather than RPC URLs (string equality) to avoid false mismatches
+  // from URL normalization differences.
   useEffect(() => {
-    if (!controller || !urlRpcUrl) return;
-    if (controller.rpcUrl() === urlRpcUrl) return;
+    if (!controller || !chainId) return;
+    if (controller.chainId() === chainId) return;
 
-    setRpcUrl(urlRpcUrl);
+    if (urlRpcUrl) {
+      setRpcUrl(urlRpcUrl);
+    }
 
     (async () => {
       await controller.disconnect();
       setController(undefined);
     })();
-  }, [controller, urlRpcUrl, setController, setRpcUrl]);
+  }, [controller, chainId, urlRpcUrl, setController, setRpcUrl]);
 
   const urlParamsRef = useRef<{
     theme: string | null;