diff --git a/src/oauth/xai.ts b/src/oauth/xai.ts
index 9af6b25a96..f1669c7576 100644
--- a/src/oauth/xai.ts
+++ b/src/oauth/xai.ts
@@ -14,6 +14,7 @@ const XAI_OAUTH_REFRESH_SKEW_MS = 2 * 60 * 1000;
 const TOKEN_REQUEST_TIMEOUT_MS = 30_000;
 const RETRY_AFTER_MAX_DELAY_MS = 60_000;
 const JITTER_DELAY_CAP_MS = 2_000;
+const XAI_TRUSTED_AUTH_HOSTS = new Set(["auth.x.ai", "accounts.x.ai"]);
 
 export const XAI_LOCAL_CLI_DETACH_WARNING =
   "[oauth:xai] Grok CLI credential was stale; refreshed into OpenCodex ownership. Grok CLI may require login again.";
@@ -48,10 +49,21 @@ function requestSignal(signal: AbortSignal | undefined): AbortSignal {
 }
 
 function validateXaiEndpoint(rawUrl: string): string {
-  const parsed = new URL(rawUrl);
+  let parsed: URL;
+  try {
+    parsed = new URL(rawUrl);
+  } catch {
+    throw new Error("xAI OAuth discovery returned an unparseable endpoint URL");
+  }
   const host = parsed.hostname.toLowerCase();
-  if (parsed.protocol !== "https:" || (host !== "x.ai" && !host.endsWith(".x.ai"))) {
-    throw new Error(`xAI OAuth discovery returned an unexpected endpoint: ${rawUrl}`);
+  if (
+    parsed.protocol !== "https:"
+    || parsed.username !== ""
+    || parsed.password !== ""
+    || parsed.port !== ""
+    || !XAI_TRUSTED_AUTH_HOSTS.has(host)
+  ) {
+    throw new Error(`xAI OAuth discovery returned an unexpected endpoint (host: ${host || "none"})`);
   }
   return parsed.toString();
 }
diff --git a/tests/providers/xai/xai-oauth-retry.test.ts b/tests/providers/xai/xai-oauth-retry.test.ts
index fd912d22f9..b5ecfa0efb 100644
--- a/tests/providers/xai/xai-oauth-retry.test.ts
+++ b/tests/providers/xai/xai-oauth-retry.test.ts
@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, test } from "bun:test";
-import { postXaiToken, XaiTokenRequestError } from "../../../src/oauth/xai";
+import { discoverXaiOAuthEndpoints, postXaiToken, XaiTokenRequestError } from "../../../src/oauth/xai";
 const original=globalThis.fetch; afterEach(()=>{globalThis.fetch=original;});
 function queue(items:Array<Response|Error>){let n=0;globalThis.fetch=(async()=>{const x=items[n++]!;if(x instanceof Error)throw x;return x;}) as typeof fetch;return()=>n;}
 const body={grant_type:"refresh_token",client_id:"client",refresh_token:"secret"}; const ok=()=>new Response(JSON.stringify({access_token:"a",refresh_token:"r",expires_in:3600}));
@@ -38,3 +38,15 @@ describe("xAI abort handling",()=>{
  test("caller aborted before a 429 backoff does not sleep",async()=>{const c=new AbortController();let calls=0;globalThis.fetch=(async()=>{calls++;c.abort();return new Response("",{status:429,headers:{"retry-after":"60"}});}) as typeof fetch;const d:number[]=[];await expect(postXaiToken("https://auth.x.ai/token",body,c.signal,{sleep:async x=>{d.push(x)}})).rejects.toMatchObject({status:429});expect(calls).toBe(1);expect(d).toEqual([]);});
  test("caller abort during a Retry-After wait rejects promptly",async()=>{const c=new AbortController();const reason=new Error("cancel during wait");globalThis.fetch=(async()=>new Response("",{status:429,headers:{"retry-after":"60"}})) as typeof fetch;const d:number[]=[];const pending=postXaiToken("https://auth.x.ai/token",body,c.signal,{sleep:async x=>{d.push(x);await new Promise(()=>{});}});while(!d.length)await Bun.sleep(1);c.abort(reason);await expect(pending).rejects.toBe(reason);expect(d).toEqual([60000]);});
 });
+
+describe("xAI endpoint validation",()=>{
+ const discover=(authorization_endpoint:string,token_endpoint:string)=>{globalThis.fetch=(async()=>Response.json({authorization_endpoint,token_endpoint})) as typeof fetch;return discoverXaiOAuthEndpoints();};
+ test("accepts the live discovery shape",async()=>{const d=await discover("https://auth.x.ai/oauth2/authorize","https://auth.x.ai/oauth2/token");expect(d).toEqual({authorizationEndpoint:"https://auth.x.ai/oauth2/authorize",tokenEndpoint:"https://auth.x.ai/oauth2/token"});});
+ test("accepts the allow-listed accounts host",async()=>{const d=await discover("https://accounts.x.ai/oauth2/authorize","https://accounts.x.ai/oauth2/token");expect(d.tokenEndpoint).toBe("https://accounts.x.ai/oauth2/token");});
+ test("rejects plain http",async()=>{await expect(discover("http://auth.x.ai/oauth2/authorize","http://auth.x.ai/oauth2/token")).rejects.toThrow(/unexpected endpoint/);});
+ test("rejects the apex host",async()=>{await expect(discover("https://x.ai/oauth2/authorize","https://x.ai/oauth2/token")).rejects.toThrow(/unexpected endpoint/);});
+ test("rejects unlisted subdomains",async()=>{await expect(discover("https://evil.x.ai/token","https://api.x.ai/token")).rejects.toThrow(/unexpected endpoint/);});
+ test("rejects embedded userinfo without echoing it",async()=>{const u="https://u:p@"+"auth.x.ai/oauth2/token";await expect(discover(u,u)).rejects.toThrowError(/unexpected endpoint/);try{await discover(u,u);expect.unreachable();}catch(error){const m=(error as Error).message;expect(m).not.toContain("u:p");expect(m).not.toContain("p@auth");}});
+ test("rejects an explicit port",async()=>{await expect(discover("https://auth.x.ai:8443/oauth2/authorize","https://auth.x.ai:8443/oauth2/token")).rejects.toThrow(/unexpected endpoint/);});
+ test("malformed discovery URL is a generic Error, not a TypeError",async()=>{await expect(discover("not a url","::")).rejects.toThrowError(/unparseable endpoint URL/);try{await discover("not a url","::");expect.unreachable();}catch(error){expect(error).toBeInstanceOf(Error);expect(error).not.toBeInstanceOf(TypeError);expect(error).not.toBeInstanceOf(XaiTokenRequestError);}});
+});