diff --git a/open-sse/executors/github.ts b/open-sse/executors/github.ts
index f4ab762f80..036998c417 100644
--- a/open-sse/executors/github.ts
+++ b/open-sse/executors/github.ts
@@ -27,7 +27,10 @@ export class GithubExecutor extends BaseExecutor {
 
   buildUrl(model: string, _stream: boolean, _urlIndex = 0) {
     const targetFormat = getModelTargetFormat("gh", model);
-    if (targetFormat === "openai-responses") {
+    // 9router#102: Copilot Codex models advertise supported_endpoints: ["/responses"]
+    // and 400 on /chat/completions. Route any *-codex id to /responses even when it
+    // isn't in the curated registry, so newly-shipped Codex models work out of the box.
+    if (targetFormat === "openai-responses" || /codex/i.test(model)) {
       return (
         this.config.responsesBaseUrl ||
         this.config.baseUrl?.replace(/\/chat\/completions\/?$/, "/responses") ||
diff --git a/tests/unit/executor-github.test.ts b/tests/unit/executor-github.test.ts
index 6d8194e043..ddcbf272cc 100644
--- a/tests/unit/executor-github.test.ts
+++ b/tests/unit/executor-github.test.ts
@@ -71,6 +71,33 @@ test("GithubExecutor.buildUrl keeps GitHub Claude Opus 4.6 on /chat/completions"
   assert.equal(url, "https://api.githubcopilot.com/chat/completions");
 });
 
+test("GithubExecutor.buildUrl routes unlisted Codex models to /responses (9router#102)", () => {
+  // Copilot Codex models advertise supported_endpoints: ["/responses"]. When such
+  // a model isn't in the curated gh registry, getModelTargetFormat returns null and
+  // the request fell through to /chat/completions -> upstream 400 "model <id> is not
+  // accessible via the /chat/completions endpoint". Any *-codex id must route to
+  // /responses regardless of whether it's explicitly registered.
+  const executor = new GithubExecutor();
+  for (const model of [
+    "gpt-5-codex",
+    "gpt-5.1-codex",
+    "gpt-5.1-codex-mini",
+    "gpt-5.1-codex-max",
+    "gpt-5.2-codex",
+  ]) {
+    assert.equal(
+      executor.buildUrl(model, true),
+      "https://api.githubcopilot.com/responses",
+      `${model} must route to /responses`
+    );
+  }
+  // Non-codex unlisted models keep the chat/completions default.
+  assert.equal(
+    executor.buildUrl("some-random-chat-model", true),
+    "https://api.githubcopilot.com/chat/completions"
+  );
+});
+
 test("GithubExecutor.transformRequest injects JSON response instructions for Claude and strips reasoning fields", () => {
   const executor = new GithubExecutor();
   const body = {