diff --git a/src/server/__tests__/haha-openai-oauth-api.test.ts b/src/server/__tests__/haha-openai-oauth-api.test.ts
index 3a605561..e7b19950 100644
--- a/src/server/__tests__/haha-openai-oauth-api.test.ts
+++ b/src/server/__tests__/haha-openai-oauth-api.test.ts
@@ -83,7 +83,8 @@ describe('POST /api/haha-openai-oauth/start', () => {
     expect(data.authorizeUrl).toContain(
       encodeURIComponent('http://localhost:54321/auth/callback'),
     )
-    expect(data.state).toMatch(/^[A-Za-z0-9_-]+$/)
+    expect(data.authorizeUrl).not.toContain('originator=')
+    expect(data.state).toMatch(/^[a-f0-9]{64}$/)
   })
 
   test('400 if serverPort missing', async () => {
diff --git a/src/server/__tests__/haha-openai-oauth-service.test.ts b/src/server/__tests__/haha-openai-oauth-service.test.ts
index 8bd331b7..db5de249 100644
--- a/src/server/__tests__/haha-openai-oauth-service.test.ts
+++ b/src/server/__tests__/haha-openai-oauth-service.test.ts
@@ -113,8 +113,8 @@ describe('HahaOpenAIOAuthService — session management', () => {
 
   test('startSession creates session with PKCE + state', () => {
     const session = service.startSession({ serverPort: 54321 })
-    expect(session.state).toMatch(/^[A-Za-z0-9_-]{43}$/)
-    expect(session.codeVerifier).toMatch(/^[A-Za-z0-9_-]{43}$/)
+    expect(session.state).toMatch(/^[a-f0-9]{64}$/)
+    expect(session.codeVerifier).toMatch(/^[a-f0-9]{128}$/)
     expect(session.authorizeUrl).toContain('code_challenge_method=S256')
     expect(session.authorizeUrl).toContain(
       `state=${encodeURIComponent(session.state)}`,
@@ -125,6 +125,7 @@ describe('HahaOpenAIOAuthService — session management', () => {
     expect(session.authorizeUrl).toContain(
       encodeURIComponent('http://localhost:54321/auth/callback'),
     )
+    expect(session.authorizeUrl).not.toContain('originator=')
   })
 
   test('getSession returns stored session by state', () => {
diff --git a/src/server/services/hahaOpenAIOAuthService.ts b/src/server/services/hahaOpenAIOAuthService.ts
index 74738b9c..4f71b252 100644
--- a/src/server/services/hahaOpenAIOAuthService.ts
+++ b/src/server/services/hahaOpenAIOAuthService.ts
@@ -12,19 +12,15 @@
 import * as fs from 'fs/promises'
 import * as os from 'os'
 import * as path from 'path'
-import {
-  generateCodeVerifier,
-  generateCodeChallenge,
-  generateState,
-} from '../../services/oauth/crypto.js'
 import {
   buildOpenAIAuthorizeUrl,
   exchangeOpenAICodeForTokens,
+  generateOpenAICodeVerifier,
+  generateOpenAIState,
   refreshOpenAITokens,
   isOpenAITokenExpired,
   normalizeOpenAITokens,
   withRefreshedAccessToken,
-  OPENAI_CODEX_OAUTH_PORT,
   OPENAI_CODEX_REDIRECT_PATH,
 } from '../../services/openaiAuth/client.js'
 import type { OpenAIOAuthTokenResponse } from '../../services/openaiAuth/types.js'
@@ -108,8 +104,8 @@ export class HahaOpenAIOAuthService {
   startSession({ serverPort }: { serverPort: number }): OpenAIOAuthSession {
     this.pruneExpiredSessions()
 
-    const codeVerifier = generateCodeVerifier()
-    const state = generateState()
+    const codeVerifier = generateOpenAICodeVerifier()
+    const state = generateOpenAIState()
 
     const redirectUri = `http://localhost:${serverPort}${OPENAI_CODEX_REDIRECT_PATH}`
     const authorizeUrl = buildOpenAIAuthorizeUrl({
diff --git a/src/services/openaiAuth/client.test.ts b/src/services/openaiAuth/client.test.ts
new file mode 100644
index 00000000..2ea7bd61
--- /dev/null
+++ b/src/services/openaiAuth/client.test.ts
@@ -0,0 +1,40 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  buildOpenAIAuthorizeUrl,
+  generateOpenAICodeVerifier,
+  generateOpenAIState,
+  OPENAI_CODEX_CLIENT_ID,
+} from './client.js'
+
+describe('OpenAI Codex OAuth client', () => {
+  test('generates hex PKCE verifier and state like the Codex-compatible flow', () => {
+    const verifier = generateOpenAICodeVerifier()
+    const state = generateOpenAIState()
+
+    expect(verifier).toMatch(/^[a-f0-9]{128}$/)
+    expect(state).toMatch(/^[a-f0-9]{64}$/)
+  })
+
+  test('builds authorize URL without non-Codex originator parameter', () => {
+    const authorizeUrl = buildOpenAIAuthorizeUrl({
+      redirectUri: 'http://localhost:1455/auth/callback',
+      codeVerifier: 'a'.repeat(128),
+      state: 'b'.repeat(64),
+    })
+    const parsed = new URL(authorizeUrl)
+    const params = parsed.searchParams
+
+    expect(parsed.origin + parsed.pathname).toBe(
+      'https://auth.openai.com/oauth/authorize',
+    )
+    expect(params.get('client_id')).toBe(OPENAI_CODEX_CLIENT_ID)
+    expect(params.get('redirect_uri')).toBe(
+      'http://localhost:1455/auth/callback',
+    )
+    expect(params.get('scope')).toBe('openid profile email offline_access')
+    expect(params.get('code_challenge_method')).toBe('S256')
+    expect(params.get('id_token_add_organizations')).toBe('true')
+    expect(params.get('codex_cli_simplified_flow')).toBe('true')
+    expect(params.has('originator')).toBe(false)
+  })
+})
diff --git a/src/services/openaiAuth/client.ts b/src/services/openaiAuth/client.ts
index e83a148c..459800e8 100644
--- a/src/services/openaiAuth/client.ts
+++ b/src/services/openaiAuth/client.ts
@@ -1,3 +1,4 @@
+import { randomBytes } from 'crypto'
 import { generateCodeChallenge } from '../oauth/crypto.js'
 import type {
   OpenAIJwtClaims,
@@ -14,6 +15,14 @@ export const OPENAI_CODEX_REDIRECT_PATH = '/auth/callback'
 
 const DEFAULT_TOKEN_LIFETIME_MS = 3600 * 1000
 
+export function generateOpenAIState(): string {
+  return randomBytes(32).toString('hex')
+}
+
+export function generateOpenAICodeVerifier(): string {
+  return randomBytes(64).toString('hex')
+}
+
 export function buildOpenAIAuthorizeUrl(input: {
   redirectUri: string
   codeVerifier: string
@@ -29,7 +38,6 @@ export function buildOpenAIAuthorizeUrl(input: {
     id_token_add_organizations: 'true',
     codex_cli_simplified_flow: 'true',
     state: input.state,
-    originator: 'opencode',
   })
 
   return `${OPENAI_AUTH_ISSUER}/oauth/authorize?${params.toString()}`
diff --git a/src/services/openaiAuth/index.ts b/src/services/openaiAuth/index.ts
index 95be8ec5..8837f99f 100644
--- a/src/services/openaiAuth/index.ts
+++ b/src/services/openaiAuth/index.ts
@@ -1,9 +1,10 @@
 import { openBrowser } from '../../utils/browser.js'
 import { AuthCodeListener } from '../oauth/auth-code-listener.js'
-import { generateCodeVerifier, generateState } from '../oauth/crypto.js'
 import {
   buildOpenAIAuthorizeUrl,
   exchangeOpenAICodeForTokens,
+  generateOpenAICodeVerifier,
+  generateOpenAIState,
   isOpenAITokenExpired,
   OPENAI_CODEX_OAUTH_PORT,
   OPENAI_CODEX_REDIRECT_PATH,
@@ -59,7 +60,7 @@ export class OpenAIOAuthService {
     null
 
   constructor() {
-    this.codeVerifier = generateCodeVerifier()
+    this.codeVerifier = generateOpenAICodeVerifier()
   }
 
   async startOAuthFlow(
@@ -71,7 +72,7 @@ export class OpenAIOAuthService {
     this.authCodeListener = new AuthCodeListener(OPENAI_CODEX_REDIRECT_PATH)
     this.port = await this.authCodeListener.start(OPENAI_CODEX_OAUTH_PORT)
 
-    const state = generateState()
+    const state = generateOpenAIState()
     const redirectUri = `http://localhost:${this.port}${OPENAI_CODEX_REDIRECT_PATH}`
     const authorizeUrl = buildOpenAIAuthorizeUrl({
       redirectUri,