diff --git a/src/server/claude-messages.ts b/src/server/claude-messages.ts
index 5e3074bec4a..ec81a456c44 100644
--- a/src/server/claude-messages.ts
+++ b/src/server/claude-messages.ts
@@ -732,6 +732,7 @@ async function handleClaudeMessagesWithBudget(
     // Without this the replay would look native and a Responses-scoped wire default
     // would fire, disagreeing with the pre-flight decision above.
     inboundWire: "anthropic",
+    stripClaudeMainAuthForNoncanonicalForward: true,
     translatorBudget,
     ...(logIds ? { onFirstOutput: () => recordFirstOutput(logCtx, logIds.start) } : {}),
     onNativePassthroughTerminal: status => finalizeNativeLog(httpStatusForTerminalStatus(status), { terminalStatus: status, closeReason: "terminal" }),
diff --git a/src/server/responses/core.ts b/src/server/responses/core.ts
index 327376fc596..01a58b79490 100644
--- a/src/server/responses/core.ts
+++ b/src/server/responses/core.ts
@@ -631,6 +631,12 @@ export interface HandleResponsesOptions {
   inboundWire?: InboundWire;
   /** Internal transport identity for route-scoped upstream compatibility policy. */
   inboundTransport?: "websocket";
+  /**
+   * Claude replay may add native-main auth so OpenAI sidecars remain available.
+   * Strip only that internal credential when the final route is a noncanonical
+   * forward destination; final routing can differ from Claude's preflight route.
+   */
+  stripClaudeMainAuthForNoncanonicalForward?: boolean;
   /** Internal recursion guard; callers outside this module must not set it. */
   comboAttempt?: boolean;
   /** Internal combo handoff: allow a later same-provider model after a reset-derived 429/402. */
@@ -1701,7 +1707,24 @@ async function handleResponsesInner(
     parsed.options.promptCacheKey,
     route.providerName === "github-copilot" ? getOAuthCredentialApiBaseUrl(route.providerName) : undefined,
   );
-  const adapterProvider = resolveWireProtocolOverride(route.providerName, route.modelId, route.provider, inboundWire);
+  let adapterProvider = resolveWireProtocolOverride(route.providerName, route.modelId, route.provider, inboundWire);
+  const stripClaudeMainAuth = options.stripClaudeMainAuthForNoncanonicalForward === true
+    && adapterProvider.adapter === "openai-responses"
+    && adapterProvider.authMode === "forward"
+    && !isCanonicalOpenAiForwardProvider(adapterProvider);
+  if (stripClaudeMainAuth) {
+    releaseCodexAuthContextProbeLease(authCtx);
+    authCtx = { kind: "main", accountId: null };
+    route.provider = stripCodexRuntimeProviderFields(route.provider);
+    adapterProvider = stripCodexRuntimeProviderFields(adapterProvider);
+    selectedForwardHeaders = new Headers(selectedForwardHeaders);
+    selectedForwardHeaders.delete("authorization");
+    selectedForwardHeaders.delete("chatgpt-account-id");
+    delete route.codexAccountMode;
+    delete route.codexAccountId;
+    delete route.codexAccountNamespace;
+    logCtx.provider = route.providerName;
+  }
   const adapter = resolveAdapter(adapterProvider, config.cacheRetention);
   logCtx.providerAdapter = adapter.name;
   // Ordinary requests receive one durable attempt only after their final initial
diff --git a/tests/claude-messages-endpoint.test.ts b/tests/claude-messages-endpoint.test.ts
index 9269160db5f..e365299c52c 100644
--- a/tests/claude-messages-endpoint.test.ts
+++ b/tests/claude-messages-endpoint.test.ts
@@ -686,6 +686,121 @@ test("native openai-responses route carries prompt_cache_key + synthesized sessi
   }
 });
 
+test("custom forward openai-responses route never receives the main ChatGPT credential", async () => {
+  writeFileSync(join(isolatedCodexHome!.path, "auth.json"), JSON.stringify({
+    tokens: { access_token: "main-secret-must-not-leave", account_id: "main-account-must-not-leave" },
+  }));
+  const captured: Array<{ authorization: string | null; accountId: string | null }> = [];
+  const upstream = Bun.serve({
+    port: 0,
+    fetch(req) {
+      captured.push({
+        authorization: req.headers.get("authorization"),
+        accountId: req.headers.get("chatgpt-account-id"),
+      });
+      return new Response([
+        'event: response.created\ndata: {"response":{"id":"resp_1","status":"in_progress"}}\n\n',
+        'event: response.output_text.delta\ndata: {"delta":"ok"}\n\n',
+        'event: response.completed\ndata: {"response":{"status":"completed","usage":{"input_tokens":1,"output_tokens":1}}}\n\n',
+      ].join(""), { headers: { "content-type": "text/event-stream" } });
+    },
+  });
+  saveConfig({
+    port: 0,
+    defaultProvider: "custom",
+    providers: {
+      custom: {
+        adapter: "openai-chat",
+        baseUrl: `${upstream.url.toString().replace(/\/$/, "")}/v1`,
+        authMode: "forward",
+        allowPrivateNetwork: true,
+        modelAdapters: { "gpt-test": "openai-responses" },
+      },
+    },
+  } as OcxConfig);
+  const server = startServer(0);
+  try {
+    const response = await fetch(new URL("/v1/messages", server.url), {
+      method: "POST",
+      headers: { "content-type": "application/json", authorization: "Bearer claude-placeholder" },
+      body: JSON.stringify({
+        model: "custom/gpt-test",
+        max_tokens: 16,
+        messages: [{ role: "user", content: "hi" }],
+      }),
+    });
+    const responseBody = await response.text();
+    expect({ status: response.status, body: responseBody }).toMatchObject({ status: 200 });
+    expect(captured).toEqual([{ authorization: null, accountId: null }]);
+  } finally {
+    await server.stop(true);
+    upstream.stop(true);
+  }
+});
+
+test("shadow-call rerouting cannot carry the main ChatGPT credential to a custom forward route", async () => {
+  writeFileSync(join(isolatedCodexHome!.path, "auth.json"), JSON.stringify({
+    tokens: { access_token: "main-secret-must-not-leave", account_id: "main-account-must-not-leave" },
+  }));
+  const captured: Array<{ authorization: string | null; accountId: string | null }> = [];
+  const upstream = Bun.serve({
+    port: 0,
+    fetch(req) {
+      captured.push({
+        authorization: req.headers.get("authorization"),
+        accountId: req.headers.get("chatgpt-account-id"),
+      });
+      return new Response([
+        'event: response.created\ndata: {"response":{"id":"resp_1","status":"in_progress"}}\n\n',
+        'event: response.output_text.delta\ndata: {"delta":"ok"}\n\n',
+        'event: response.completed\ndata: {"response":{"status":"completed","usage":{"input_tokens":1,"output_tokens":1}}}\n\n',
+      ].join(""), { headers: { "content-type": "text/event-stream" } });
+    },
+  });
+  saveConfig({
+    port: 0,
+    defaultProvider: "openai",
+    providers: {
+      openai: {
+        adapter: "openai-responses",
+        baseUrl: "https://chatgpt.com/backend-api/codex",
+        authMode: "forward",
+        codexAccountMode: "direct",
+      },
+      custom: {
+        adapter: "openai-chat",
+        baseUrl: `${upstream.url.toString().replace(/\/$/, "")}/v1`,
+        authMode: "forward",
+        allowPrivateNetwork: true,
+        modelAdapters: { "gpt-test": "openai-responses" },
+      },
+    },
+    shadowCallIntercept: {
+      enabled: true,
+      model: "custom/gpt-test",
+      sourceModels: ["gpt-5.6-luna"],
+    },
+  } as OcxConfig);
+  const server = startServer(0);
+  try {
+    const response = await fetch(new URL("/v1/messages", server.url), {
+      method: "POST",
+      headers: { "content-type": "application/json", authorization: "Bearer claude-placeholder" },
+      body: JSON.stringify({
+        model: "gpt-5.6-luna",
+        max_tokens: 16,
+        messages: [{ role: "user", content: "hi" }],
+      }),
+    });
+    const responseBody = await response.text();
+    expect({ status: response.status, body: responseBody }).toMatchObject({ status: 200 });
+    expect(captured).toEqual([{ authorization: null, accountId: null }]);
+  } finally {
+    await server.stop(true);
+    upstream.stop(true);
+  }
+});
+
 test("Claude replay owns optional main enrichment while routed work survives drain and recovery", async () => {
   resetLifecycleDrainStateForTests();
   writeFileSync(join(isolatedCodexHome!.path, "auth.json"), JSON.stringify({