diff --git a/open-sse/config/codexConstants.js b/open-sse/config/codexConstants.js
new file mode 100644
index 00000000000..b66322116a8
--- /dev/null
+++ b/open-sse/config/codexConstants.js
@@ -0,0 +1,3 @@
+// Keep model discovery and image requests on the same client version. GPT-5.6
+// models require >= 0.144.0 in openai/codex's models-manager/models.json.
+export const CODEX_CLIENT_VERSION = "0.144.6";
diff --git a/open-sse/handlers/imageProviders/codex.js b/open-sse/handlers/imageProviders/codex.js
index 218302abf8c..b0b769b8e8b 100644
--- a/open-sse/handlers/imageProviders/codex.js
+++ b/open-sse/handlers/imageProviders/codex.js
@@ -2,10 +2,9 @@
 import { randomUUID } from "node:crypto";
 import { nowSec } from "./_base.js";
 import { PROVIDERS } from "../../config/providers.js";
+import { CODEX_CLIENT_VERSION } from "../../config/codexConstants.js";
 
 const CODEX_RESPONSES_URL = PROVIDERS["codex"].baseUrl;
-const CODEX_USER_AGENT = "codex_cli_rs/0.136.0";
-const CODEX_VERSION = "0.136.0";
 const CODEX_ORIGINATOR = "codex_cli_rs";
 const CODEX_MODEL_SUFFIX = "-image";
 const CODEX_REF_DETAIL = "high";
@@ -156,8 +155,8 @@ export default {
       "content-type": "application/json",
       "originator": CODEX_ORIGINATOR,
       "session_id": randomUUID(),
-      "user-agent": CODEX_USER_AGENT,
-      "version": CODEX_VERSION,
+      "user-agent": `${CODEX_ORIGINATOR}/${CODEX_CLIENT_VERSION}`,
+      "version": CODEX_CLIENT_VERSION,
       "x-client-request-id": randomUUID(),
     };
   },
diff --git a/src/app/api/providers/[id]/models/route.js b/src/app/api/providers/[id]/models/route.js
index d73ec11dfac..05c0d90d7bc 100644
--- a/src/app/api/providers/[id]/models/route.js
+++ b/src/app/api/providers/[id]/models/route.js
@@ -11,6 +11,7 @@ import { resolveQoderModels } from "open-sse/services/qoderModels.js";
 import { resolveGrokCliModels } from "open-sse/services/grokCliModels.js";
 import { resolveConnectionProxyConfig } from "@/lib/network/connectionProxy";
 import { resolveCursorModels } from "open-sse/services/cursorModels.js";
+import { CODEX_CLIENT_VERSION } from "open-sse/config/codexConstants.js";
 
 const GEMINI_CLI_MODELS_URL = "https://cloudcode-pa.googleapis.com/v1internal:fetchAvailableModels";
 
@@ -18,7 +19,6 @@ const GEMINI_CLI_MODELS_URL = "https://cloudcode-pa.googleapis.com/v1internal:fe
 // value, and codex CLI's own manifest (openai/codex codex-rs/models-manager/models.json)
 // already requires 0.144.0 for its newest models, so a stale client_version here comes
 // back 200 with those entries quietly missing instead of erroring.
-const CODEX_CLIENT_VERSION = "0.144.6";
 const CODEX_MODELS_URL = `https://chatgpt.com/backend-api/codex/models?client_version=${CODEX_CLIENT_VERSION}`;
 
 const parseOpenAIStyleModels = (data) => {
diff --git a/tests/unit/image-generation.test.js b/tests/unit/image-generation.test.js
index 12dce95d66c..ba12b2116f0 100644
--- a/tests/unit/image-generation.test.js
+++ b/tests/unit/image-generation.test.js
@@ -351,7 +351,8 @@ describe("handleImageGenerationCore", () => {
         headers: expect.objectContaining({
           authorization: "Bearer codex-token",
           "chatgpt-account-id": "account-123",
-          version: "0.136.0",
+          version: "0.144.6",
+          "user-agent": "codex_cli_rs/0.144.6",
         }),
       })
     );