diff --git a/extensions/openai/openai-provider.ts b/extensions/openai/openai-provider.ts
index a34fdd725430..679e7307af74 100644
--- a/extensions/openai/openai-provider.ts
+++ b/extensions/openai/openai-provider.ts
@@ -84,7 +84,7 @@ function classifyOpenAiFailoverCode(code: string | undefined) {
 const OPENAI_MODELS_ENDPOINT = "https://api.openai.com/v1/models";
 // Keep synchronized with extensions/codex's exact @openai/codex dependency;
 // the provider contract test fails when that managed-runtime pin changes.
-const OPENAI_CODEX_CLIENT_VERSION = "0.144.6";
+const OPENAI_CODEX_CLIENT_VERSION = "0.145.0";
 const OPENAI_CODEX_MODELS_ENDPOINT = `${OPENAI_CODEX_RESPONSES_BASE_URL}/models?client_version=${OPENAI_CODEX_CLIENT_VERSION}`;
 const OPENAI_MODELS_CACHE_TTL_MS = 60_000;
 const OPENAI_CODEX_MODELS_CACHE_TTL_MS = 60_000;
diff --git a/scripts/test-projects.test-support.mjs b/scripts/test-projects.test-support.mjs
index 5fe99472e0c2..06901e9005fd 100644
--- a/scripts/test-projects.test-support.mjs
+++ b/scripts/test-projects.test-support.mjs
@@ -2350,6 +2350,7 @@ const APPCAST_TEST_TARGETS = ["test/appcast.test.ts", "test/scripts/make-appcast
 const CODEX_VERSION_CONTRACT_TEST_TARGETS = [
   "extensions/codex/src/manifest.test.ts",
   "extensions/openai/openai-provider.test.ts",
+  "test/scripts/codex-client-version-contract.test.ts",
 ];
 const SOURCE_TEST_TARGETS = new Map([
   ...PRECISE_SOURCE_TEST_TARGETS,
diff --git a/test/scripts/codex-client-version-contract.test.ts b/test/scripts/codex-client-version-contract.test.ts
new file mode 100644
index 000000000000..e8731563d075
--- /dev/null
+++ b/test/scripts/codex-client-version-contract.test.ts
@@ -0,0 +1,33 @@
+// Codex Client Version Contract tests cover cross-plugin managed version alignment.
+import fs from "node:fs";
+import { describe, expect, it } from "vitest";
+
+const CODEX_PACKAGE_JSON_URL = new URL("../../extensions/codex/package.json", import.meta.url);
+const OPENAI_PROVIDER_URL = new URL("../../extensions/openai/openai-provider.ts", import.meta.url);
+const OPENAI_CODEX_CLIENT_VERSION_PATTERN = /^const OPENAI_CODEX_CLIENT_VERSION = "([^"]+)";$/mu;
+
+function readManagedCodexVersion(): string {
+  const packageJson = JSON.parse(fs.readFileSync(CODEX_PACKAGE_JSON_URL, "utf8")) as {
+    dependencies?: Record<string, unknown>;
+  };
+  const version = packageJson.dependencies?.["@openai/codex"];
+  if (typeof version !== "string") {
+    throw new Error("extensions/codex/package.json must pin @openai/codex exactly");
+  }
+  return version;
+}
+
+function readOpenAICodexClientVersion(): string {
+  const providerSource = fs.readFileSync(OPENAI_PROVIDER_URL, "utf8");
+  const version = OPENAI_CODEX_CLIENT_VERSION_PATTERN.exec(providerSource)?.[1];
+  if (!version) {
+    throw new Error("extensions/openai/openai-provider.ts must declare the Codex client version");
+  }
+  return version;
+}
+
+describe("Codex client version contract", () => {
+  it("matches OpenAI model discovery to the managed Codex package", () => {
+    expect(readOpenAICodexClientVersion()).toBe(readManagedCodexVersion());
+  });
+});
diff --git a/test/scripts/test-projects.test.ts b/test/scripts/test-projects.test.ts
index b77048cc9669..f674c701a711 100644
--- a/test/scripts/test-projects.test.ts
+++ b/test/scripts/test-projects.test.ts
@@ -298,6 +298,7 @@ describe("scripts/test-projects changed-target routing", () => {
         targets: [
           "extensions/codex/src/manifest.test.ts",
           "extensions/openai/openai-provider.test.ts",
+          "test/scripts/codex-client-version-contract.test.ts",
         ],
       });
     },