diff --git a/open-sse/executors/antigravity.ts b/open-sse/executors/antigravity.ts
index f08ce7e576..28cba9ec38 100644
--- a/open-sse/executors/antigravity.ts
+++ b/open-sse/executors/antigravity.ts
@@ -583,6 +583,9 @@ export class AntigravityExecutor extends BaseExecutor {
             : credentials.refreshToken,
         expiresIn: typeof tokens.expires_in === "number" ? tokens.expires_in : undefined,
         projectId: credentials.projectId,
+        // Preserve providerSpecificData so a projectId stored there survives the refresh
+        // (the onCredentialsRefreshed DB write) instead of being dropped → 422 (#2480).
+        providerSpecificData: credentials.providerSpecificData,
       };
     } catch (error) {
       const message = error instanceof Error ? error.message : String(error);
diff --git a/open-sse/translator/request/openai-to-gemini.ts b/open-sse/translator/request/openai-to-gemini.ts
index 2140278d3f..cc8c744a11 100644
--- a/open-sse/translator/request/openai-to-gemini.ts
+++ b/open-sse/translator/request/openai-to-gemini.ts
@@ -508,7 +508,15 @@ function wrapInCloudCodeEnvelope(model, geminiCLI, credentials = null, isAntigra
   // Both Antigravity and Gemini CLI need the project field for the Cloud Code API.
   // For Gemini CLI, the stored projectId may be stale; the executor's transformRequest
   // refreshes it via loadCodeAssist before the request is sent to the API.
-  let projectId = credentials?.projectId;
+  // Fall back to providerSpecificData.projectId — some connections (and post-refresh
+  // credentials) store it there rather than at the top level, which otherwise produced a
+  // spurious 422 "Missing Google projectId" on the Antigravity /v1beta path (#2480).
+  const providerSpecificProjectId = (
+    credentials?.providerSpecificData as { projectId?: unknown } | undefined
+  )?.projectId;
+  let projectId =
+    credentials?.projectId ||
+    (typeof providerSpecificProjectId === "string" ? providerSpecificProjectId : "");
 
   if (!projectId) {
     console.warn(
diff --git a/tests/unit/translator-openai-to-gemini.test.ts b/tests/unit/translator-openai-to-gemini.test.ts
index daf2b12e61..993be797c1 100644
--- a/tests/unit/translator-openai-to-gemini.test.ts
+++ b/tests/unit/translator-openai-to-gemini.test.ts
@@ -891,3 +891,26 @@ test("OpenAI -> Antigravity Gemini path preserves thinkingConfig (only Claude is
   assert.equal((result as any).request?.generationConfig.thinkingConfig.thinkingBudget > 0, true);
   assert.equal((result as any).request?.generationConfig.thinkingConfig.includeThoughts, true);
 });
+
+// Regression for #2480: when projectId is stored in providerSpecificData rather than at
+// the top level of the credential record, the Antigravity Cloud Code envelope must still
+// pick it up — otherwise the /v1beta path 422s with "Missing Google projectId".
+test("openaiToAntigravityRequest falls back to providerSpecificData.projectId (#2480)", () => {
+  const result = openaiToAntigravityRequest(
+    "gemini-3.1-flash-lite",
+    { messages: [{ role: "user", content: "Hello" }] },
+    false,
+    { providerSpecificData: { projectId: "proj-from-psd" } } as any
+  );
+  assert.equal(result.project, "proj-from-psd");
+});
+
+test("openaiToAntigravityRequest prefers top-level projectId over providerSpecificData (#2480)", () => {
+  const result = openaiToAntigravityRequest(
+    "gemini-3.1-flash-lite",
+    { messages: [{ role: "user", content: "Hello" }] },
+    false,
+    { projectId: "proj-top", providerSpecificData: { projectId: "proj-psd" } } as any
+  );
+  assert.equal(result.project, "proj-top");
+});