diff --git a/open-sse/providers/registry/antigravity.js b/open-sse/providers/registry/antigravity.js
index 65f6083a..419a9779 100644
--- a/open-sse/providers/registry/antigravity.js
+++ b/open-sse/providers/registry/antigravity.js
@@ -1,4 +1,5 @@
 import { platform, arch } from "os";
+import { ANTIGRAVITY_OAUTH_CLIENT } from "../shared.js";
 
 export default {
   id: "antigravity",
@@ -10,8 +11,7 @@ export default {
     ],
     format: "antigravity",
     headers: { "User-Agent": `antigravity/1.107.0 ${platform()}/${arch()}` },
-    clientId: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
-    clientSecret: "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"
+    ...ANTIGRAVITY_OAUTH_CLIENT
   },
   models: [
     { id: "gemini-3-flash-agent", name: "Gemini 3.5 Flash (High)" },
diff --git a/open-sse/providers/registry/gemini-cli.js b/open-sse/providers/registry/gemini-cli.js
index df1269c4..bd868d3d 100644
--- a/open-sse/providers/registry/gemini-cli.js
+++ b/open-sse/providers/registry/gemini-cli.js
@@ -1,11 +1,12 @@
+import { GOOGLE_OAUTH_CLIENT } from "../shared.js";
+
 export default {
   "id": "gemini-cli",
   "alias": "gc",
   "transport": {
     "baseUrl": "https://cloudcode-pa.googleapis.com/v1internal",
     "format": "gemini-cli",
-    "clientId": "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com",
-    "clientSecret": "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"
+    ...GOOGLE_OAUTH_CLIENT
   },
   "models": [
     {
diff --git a/open-sse/providers/registry/gemini.js b/open-sse/providers/registry/gemini.js
index be3fbbb4..5fdc7e95 100644
--- a/open-sse/providers/registry/gemini.js
+++ b/open-sse/providers/registry/gemini.js
@@ -1,11 +1,12 @@
+import { GOOGLE_OAUTH_CLIENT } from "../shared.js";
+
 export default {
   "id": "gemini",
   "alias": "gemini",
   "transport": {
     "baseUrl": "https://generativelanguage.googleapis.com/v1beta/models",
     "format": "gemini",
-    "clientId": "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com",
-    "clientSecret": "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"
+    ...GOOGLE_OAUTH_CLIENT
   },
   "models": [
     {
diff --git a/open-sse/providers/shared.js b/open-sse/providers/shared.js
index e4fad1e1..d31c1856 100644
--- a/open-sse/providers/shared.js
+++ b/open-sse/providers/shared.js
@@ -46,3 +46,15 @@ export const CLAUDE_CLI_SPOOF_HEADERS = {
 
 // Shared baseUrls
 export const KIMI_CODING_BASE_URL = "https://api.kimi.com/coding/v1/messages";
+
+// Antigravity OAuth client credentials (public CLI client — duplicated in usage.js + src/lib/oauth)
+export const ANTIGRAVITY_OAUTH_CLIENT = {
+  clientId: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
+  clientSecret: "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"
+};
+
+// Gemini (Google) OAuth client credentials (public CLI client — shared by gemini, gemini-cli, src/lib/oauth)
+export const GOOGLE_OAUTH_CLIENT = {
+  clientId: "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com",
+  clientSecret: "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"
+};
diff --git a/open-sse/services/usage.js b/open-sse/services/usage.js
index 9425f09d..e994b9bc 100644
--- a/open-sse/services/usage.js
+++ b/open-sse/services/usage.js
@@ -5,6 +5,7 @@
 import { CLIENT_METADATA, getPlatformUserAgent } from "../config/appConstants.js";
 import { proxyAwareFetch } from "../utils/proxyFetch.js";
 import { resolveDefaultProfileArn } from "../config/kiroConstants.js";
+import { ANTIGRAVITY_OAUTH_CLIENT } from "../providers/shared.js";
 
 // GitHub API config
 const GITHUB_CONFIG = {
@@ -40,8 +41,7 @@ const ANTIGRAVITY_CONFIG = {
   quotaApiUrl: "https://cloudcode-pa.googleapis.com/v1internal:fetchAvailableModels",
   loadProjectApiUrl: "https://cloudcode-pa.googleapis.com/v1internal:loadCodeAssist",
   tokenUrl: "https://oauth2.googleapis.com/token",
-  clientId: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
-  clientSecret: "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",
+  ...ANTIGRAVITY_OAUTH_CLIENT,
   userAgent: getPlatformUserAgent(),
 };
 
diff --git a/src/lib/oauth/constants/oauth.js b/src/lib/oauth/constants/oauth.js
index dc825b30..66ab7134 100644
--- a/src/lib/oauth/constants/oauth.js
+++ b/src/lib/oauth/constants/oauth.js
@@ -2,6 +2,7 @@
  * OAuth Configuration Constants
  */
 import { platform, arch } from "os";
+import { ANTIGRAVITY_OAUTH_CLIENT, GOOGLE_OAUTH_CLIENT } from "open-sse/providers/shared.js";
 
 /**
  * Get the platform enum value based on the current OS.
@@ -42,8 +43,7 @@ export const CODEX_CONFIG = {
 
 // Gemini (Google) OAuth Configuration (Standard OAuth2)
 export const GEMINI_CONFIG = {
-  clientId: "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com",
-  clientSecret: "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",
+  ...GOOGLE_OAUTH_CLIENT,
   authorizeUrl: "https://accounts.google.com/o/oauth2/v2/auth",
   tokenUrl: "https://oauth2.googleapis.com/token",
   userInfoUrl: "https://www.googleapis.com/oauth2/v1/userinfo",
@@ -94,8 +94,7 @@ export const IFLOW_CONFIG = {
 
 // Antigravity OAuth Configuration (Standard OAuth2 with Google)
 export const ANTIGRAVITY_CONFIG = {
-  clientId: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
-  clientSecret: "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",
+  ...ANTIGRAVITY_OAUTH_CLIENT,
   authorizeUrl: "https://accounts.google.com/o/oauth2/v2/auth",
   tokenUrl: "https://oauth2.googleapis.com/token",
   userInfoUrl: "https://www.googleapis.com/oauth2/v1/userinfo",
diff --git a/tests/unit/antigravity-oauth-client.test.js b/tests/unit/antigravity-oauth-client.test.js
new file mode 100644
index 00000000..a43bd8ff
--- /dev/null
+++ b/tests/unit/antigravity-oauth-client.test.js
@@ -0,0 +1,49 @@
+// Guards the deduped Antigravity OAuth client: same values across all 3 sources after refactor.
+import { describe, it, expect } from "vitest";
+
+const EXPECTED = {
+  clientId: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
+  clientSecret: "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",
+};
+const GOOGLE = {
+  clientId: "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com",
+  clientSecret: "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",
+};
+
+describe("antigravity oauth client (deduped)", () => {
+  it("shared source holds the canonical credentials", async () => {
+    const { ANTIGRAVITY_OAUTH_CLIENT } = await import("../../open-sse/providers/shared.js");
+    expect(ANTIGRAVITY_OAUTH_CLIENT).toEqual(EXPECTED);
+  });
+
+  it("registry transport keeps clientId/clientSecret", async () => {
+    const ag = (await import("../../open-sse/providers/registry/antigravity.js")).default;
+    expect(ag.transport.clientId).toBe(EXPECTED.clientId);
+    expect(ag.transport.clientSecret).toBe(EXPECTED.clientSecret);
+  });
+
+  it("google client shared by gemini + gemini-cli", async () => {
+    const { GOOGLE_OAUTH_CLIENT } = await import("../../open-sse/providers/shared.js");
+    expect(GOOGLE_OAUTH_CLIENT).toEqual(GOOGLE);
+    const gemini = (await import("../../open-sse/providers/registry/gemini.js")).default;
+    const gc = (await import("../../open-sse/providers/registry/gemini-cli.js")).default;
+    expect(gemini.transport.clientSecret).toBe(GOOGLE.clientSecret);
+    expect(gc.transport.clientSecret).toBe(GOOGLE.clientSecret);
+  });
+
+  // Vitest can't resolve the `@/` alias used inside oauth.js (pre-existing infra gap),
+  // so guard the refactor textually: it must spread the shared client + keep other fields.
+  it("src oauth.js imports shared client + keeps full shape", async () => {
+    const { readFileSync } = await import("node:fs");
+    const { fileURLToPath } = await import("node:url");
+    const { dirname, join } = await import("node:path");
+    const here = dirname(fileURLToPath(import.meta.url));
+    const src = readFileSync(join(here, "../../src/lib/oauth/constants/oauth.js"), "utf8");
+    expect(src).toContain('import { ANTIGRAVITY_OAUTH_CLIENT, GOOGLE_OAUTH_CLIENT } from "open-sse/providers/shared.js"');
+    expect(src).toContain("...ANTIGRAVITY_OAUTH_CLIENT");
+    expect(src).toContain("...GOOGLE_OAUTH_CLIENT");
+    expect(src).toContain('authorizeUrl: "https://accounts.google.com/o/oauth2/v2/auth"');
+    expect(src).not.toContain(EXPECTED.clientSecret); // antigravity secret no longer hardcoded here
+    expect(src).not.toContain(GOOGLE.clientSecret);   // gemini secret no longer hardcoded here
+  });
+});