diff --git a/src/commands/provider/provider.test.tsx b/src/commands/provider/provider.test.tsx
index 7b4fa1be..6597fada 100644
--- a/src/commands/provider/provider.test.tsx
+++ b/src/commands/provider/provider.test.tsx
@@ -264,7 +264,7 @@ test('buildCurrentProviderSummary labels generic local openai-compatible provide
   expect(summary.endpointLabel).toBe('http://127.0.0.1:8080/v1')
 })
 
-test('buildCurrentProviderSummary does not relabel local gpt-5.4 providers as Codex', () => {
+test('buildCurrentProviderSummary does not relabel local gpt-5.4 providers as Codex when custom base URL is set', () => {
   const summary = buildCurrentProviderSummary({
     processEnv: {
       CLAUDE_CODE_USE_OPENAI: '1',
diff --git a/src/components/StartupScreen.ts b/src/components/StartupScreen.ts
index 506937e7..59f89739 100644
--- a/src/components/StartupScreen.ts
+++ b/src/components/StartupScreen.ts
@@ -5,7 +5,7 @@
  * Addresses: https://github.com/Gitlawb/openclaude/issues/55
  */
 
-import { isLocalProviderUrl } from '../services/api/providerConfig.js'
+import { isLocalProviderUrl, resolveProviderRequest } from '../services/api/providerConfig.js'
 import { getLocalOpenAICompatibleProviderLabel } from '../utils/providerDiscovery.js'
 import { getSettings_DEPRECATED } from '../utils/settings/settings.js'
 import { parseUserSpecifiedModel } from '../utils/model/model.js'
@@ -110,10 +110,17 @@ function detectProvider(): { name: string; model: string; baseUrl: string; isLoc
 
   if (useOpenAI) {
     const rawModel = process.env.OPENAI_MODEL || 'gpt-4o'
-    const baseUrl = process.env.OPENAI_BASE_URL || 'https://api.openai.com/v1'
+    const resolvedRequest = resolveProviderRequest({
+      model: rawModel,
+      baseUrl: process.env.OPENAI_BASE_URL,
+    })
+    const baseUrl = resolvedRequest.baseUrl
     const isLocal = isLocalProviderUrl(baseUrl)
     let name = 'OpenAI'
-    if (/deepseek/i.test(baseUrl) || /deepseek/i.test(rawModel))       name = 'DeepSeek'
+    // Override to Codex when resolved endpoint is Codex
+    if (resolvedRequest.transport === 'codex_responses' || baseUrl.includes('chatgpt.com/backend-api/codex')) {
+      name = 'Codex'
+    } else if (/deepseek/i.test(baseUrl) || /deepseek/i.test(rawModel))       name = 'DeepSeek'
     else if (/openrouter/i.test(baseUrl))                             name = 'OpenRouter'
     else if (/together/i.test(baseUrl))                               name = 'Together AI'
     else if (/groq/i.test(baseUrl))                                   name = 'Groq'
@@ -123,26 +130,9 @@ function detectProvider(): { name: string; model: string; baseUrl: string; isLoc
     else if (isLocal)                                                  name = getLocalOpenAICompatibleProviderLabel(baseUrl)
     
     // Resolve model alias to actual model name + reasoning effort
-    let displayModel = rawModel
-    const codexAliases: Record<string, { model: string; reasoningEffort?: string }> = {
-      codexplan: { model: 'gpt-5.4', reasoningEffort: 'high' },
-      'gpt-5.4': { model: 'gpt-5.4', reasoningEffort: 'high' },
-      'gpt-5.3-codex': { model: 'gpt-5.3-codex', reasoningEffort: 'high' },
-      'gpt-5.3-codex-spark': { model: 'gpt-5.3-codex-spark' },
-      codexspark: { model: 'gpt-5.3-codex-spark' },
-      'gpt-5.2-codex': { model: 'gpt-5.2-codex', reasoningEffort: 'high' },
-      'gpt-5.1-codex-max': { model: 'gpt-5.1-codex-max', reasoningEffort: 'high' },
-      'gpt-5.1-codex-mini': { model: 'gpt-5.1-codex-mini' },
-      'gpt-5.4-mini': { model: 'gpt-5.4-mini', reasoningEffort: 'medium' },
-      'gpt-5.2': { model: 'gpt-5.2', reasoningEffort: 'medium' },
-    }
-    const alias = rawModel.toLowerCase()
-    if (alias in codexAliases) {
-      const resolved = codexAliases[alias]
-      displayModel = resolved.model
-      if (resolved.reasoningEffort) {
-        displayModel = `${displayModel} (${resolved.reasoningEffort})`
-      }
+    let displayModel = resolvedRequest.resolvedModel
+    if (resolvedRequest.reasoning?.effort) {
+      displayModel = `${displayModel} (${resolvedRequest.reasoning.effort})`
     }
     
     return { name, model: displayModel, baseUrl, isLocal }
diff --git a/src/services/api/codexShim.test.ts b/src/services/api/codexShim.test.ts
index 7a0ba1f5..a135425b 100644
--- a/src/services/api/codexShim.test.ts
+++ b/src/services/api/codexShim.test.ts
@@ -18,6 +18,7 @@ const originalEnv = {
   OPENAI_BASE_URL: process.env.OPENAI_BASE_URL,
   OPENAI_API_BASE: process.env.OPENAI_API_BASE,
   CLAUDE_CODE_USE_GITHUB: process.env.CLAUDE_CODE_USE_GITHUB,
+  OPENAI_MODEL: process.env.OPENAI_MODEL,
 }
 
 afterEach(() => {
@@ -30,6 +31,9 @@ afterEach(() => {
   if (originalEnv.CLAUDE_CODE_USE_GITHUB === undefined) delete process.env.CLAUDE_CODE_USE_GITHUB
   else process.env.CLAUDE_CODE_USE_GITHUB = originalEnv.CLAUDE_CODE_USE_GITHUB
 
+  if (originalEnv.OPENAI_MODEL === undefined) delete process.env.OPENAI_MODEL
+  else process.env.OPENAI_MODEL = originalEnv.OPENAI_MODEL
+
   while (tempDirs.length > 0) {
     const dir = tempDirs.pop()
     if (dir) rmSync(dir, { recursive: true, force: true })
@@ -84,6 +88,18 @@ describe('Codex provider config', () => {
     expect(resolved.transport).toBe('codex_responses')
     expect(resolved.resolvedModel).toBe('gpt-5.4')
     expect(resolved.reasoning).toEqual({ effort: 'high' })
+    expect(resolved.baseUrl).toBe('https://chatgpt.com/backend-api/codex')
+  })
+
+  test('resolves codexspark alias to Codex transport with Codex base URL', () => {
+    delete process.env.OPENAI_BASE_URL
+    delete process.env.OPENAI_API_BASE
+    delete process.env.CLAUDE_CODE_USE_GITHUB
+
+    const resolved = resolveProviderRequest({ model: 'codexspark' })
+    expect(resolved.transport).toBe('codex_responses')
+    expect(resolved.resolvedModel).toBe('gpt-5.3-codex-spark')
+    expect(resolved.baseUrl).toBe('https://chatgpt.com/backend-api/codex')
   })
 
   test('does not force Codex transport when a local non-Codex base URL is explicit', () => {
@@ -118,6 +134,37 @@ describe('Codex provider config', () => {
     expect(resolved.baseUrl).toBe('https://chatgpt.com/backend-api/codex')
   })
 
+  test('default gpt-4o uses OpenAI base URL (no regression)', () => {
+    delete process.env.OPENAI_BASE_URL
+    delete process.env.CLAUDE_CODE_USE_GITHUB
+
+    const resolved = resolveProviderRequest({ model: 'gpt-4o' })
+    expect(resolved.transport).toBe('chat_completions')
+    expect(resolved.baseUrl).toBe('https://api.openai.com/v1')
+    expect(resolved.resolvedModel).toBe('gpt-4o')
+  })
+
+  test('resolves codexplan from env var OPENAI_MODEL to Codex endpoint', () => {
+    process.env.OPENAI_MODEL = 'codexplan'
+    delete process.env.OPENAI_BASE_URL
+    delete process.env.CLAUDE_CODE_USE_GITHUB
+
+    const resolved = resolveProviderRequest()
+    expect(resolved.transport).toBe('codex_responses')
+    expect(resolved.baseUrl).toBe('https://chatgpt.com/backend-api/codex')
+    expect(resolved.resolvedModel).toBe('gpt-5.4')
+  })
+
+  test('does not override custom base URL for codexplan (e.g., local provider)', () => {
+    process.env.OPENAI_MODEL = 'codexplan'
+    process.env.OPENAI_BASE_URL = 'http://localhost:11434/v1'
+    delete process.env.CLAUDE_CODE_USE_GITHUB
+
+    const resolved = resolveProviderRequest()
+    expect(resolved.transport).toBe('chat_completions')
+    expect(resolved.baseUrl).toBe('http://localhost:11434/v1')
+  })
+
   test('loads Codex credentials from auth.json fallback', () => {
     const authPath = createTempAuthJson({
       tokens: {
diff --git a/src/services/api/providerConfig.ts b/src/services/api/providerConfig.ts
index b1d56bfc..d17b71a5 100644
--- a/src/services/api/providerConfig.ts
+++ b/src/services/api/providerConfig.ts
@@ -60,6 +60,8 @@ const CODEX_ALIAS_MODELS: Record<
 type CodexAlias = keyof typeof CODEX_ALIAS_MODELS
 type ReasoningEffort = 'low' | 'medium' | 'high' | 'xhigh'
 
+const OPENAI_CODEX_SHORTCUT_ALIASES = new Set(['codexplan', 'codexspark'])
+
 export type ProviderTransport = 'chat_completions' | 'codex_responses'
 
 export type ResolvedProviderRequest = {
@@ -220,6 +222,12 @@ export function isCodexAlias(model: string): boolean {
   return base in CODEX_ALIAS_MODELS
 }
 
+function isOpenAICodexShortcutAlias(model: string): boolean {
+  const normalized = model.trim().toLowerCase()
+  const base = normalized.split('?', 1)[0] ?? normalized
+  return OPENAI_CODEX_SHORTCUT_ALIASES.has(base)
+}
+
 export function shouldUseCodexTransport(
   model: string,
   baseUrl: string | undefined,
@@ -367,13 +375,41 @@ export function resolveProviderRequest(options?: {
     options?.fallbackModel?.trim() ||
     (isGithubMode ? 'github:copilot' : 'gpt-4o')
   const descriptor = parseModelDescriptor(requestedModel)
-  const rawBaseUrl =
-    asEnvUrl(options?.baseUrl) ??
+  const explicitBaseUrl = asEnvUrl(options?.baseUrl)
+  const envBaseUrlRaw =
+    explicitBaseUrl ??
     asEnvUrl(
-      isMistralMode ? (process.env.MISTRAL_BASE_URL ?? DEFAULT_MISTRAL_BASE_URL) : process.env.OPENAI_BASE_URL,
+      isMistralMode
+        ? (process.env.MISTRAL_BASE_URL ?? DEFAULT_MISTRAL_BASE_URL)
+        : process.env.OPENAI_BASE_URL
     ) ??
     asEnvUrl(process.env.OPENAI_API_BASE)
 
+  const isCodexModelForGithub = isGithubMode && isCodexAlias(requestedModel)
+  const envBaseUrl =
+    isCodexModelForGithub && envBaseUrlRaw && getGithubEndpointType(envBaseUrlRaw) === 'custom'
+      ? undefined
+      : envBaseUrlRaw
+
+  const rawBaseUrl = explicitBaseUrl ?? envBaseUrl
+
+  const shellModel = process.env.OPENAI_MODEL?.trim() ?? ''
+  const envIsCodexShortcut = isOpenAICodexShortcutAlias(shellModel)
+  const envResolvedCodexModel = envIsCodexShortcut
+    ? parseModelDescriptor(shellModel).baseModel
+    : null
+  const requestedMatchesEnvCodexShortcut =
+    Boolean(options?.model) &&
+    Boolean(envResolvedCodexModel) &&
+    descriptor.baseModel === envResolvedCodexModel
+  const isCodexAliasModel =
+    isOpenAICodexShortcutAlias(requestedModel) || requestedMatchesEnvCodexShortcut
+  const hasUserSetBaseUrl = rawBaseUrl && rawBaseUrl !== DEFAULT_OPENAI_BASE_URL
+  const finalBaseUrl =
+    !isGithubMode && isCodexAliasModel && !hasUserSetBaseUrl
+      ? DEFAULT_CODEX_BASE_URL
+      : rawBaseUrl
+
   const githubEndpointType = isGithubMode
     ? getGithubEndpointType(rawBaseUrl)
     : 'custom'
@@ -386,7 +422,7 @@ export function resolveProviderRequest(options?: {
     : requestedModel
 
   const transport: ProviderTransport =
-    shouldUseCodexTransport(requestedModel, rawBaseUrl) ||
+    shouldUseCodexTransport(requestedModel, finalBaseUrl) ||
       (isGithubCopilot && shouldUseGithubResponsesApi(githubResolvedModel))
       ? 'codex_responses'
       : 'chat_completions'
@@ -410,7 +446,7 @@ export function resolveProviderRequest(options?: {
     requestedModel,
     resolvedModel,
     baseUrl:
-      (rawBaseUrl ??
+      (finalBaseUrl ??
         (isGithubCopilot && transport === 'codex_responses'
           ? GITHUB_COPILOT_BASE_URL
           : (isGithubMode