diff --git a/backend/internal/handler/openai_codex_models_handler.go b/backend/internal/handler/openai_codex_models_handler.go
new file mode 100644
index 0000000000..e64c555d14
--- /dev/null
+++ b/backend/internal/handler/openai_codex_models_handler.go
@@ -0,0 +1,53 @@
+package handler
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
+	middleware2 "github.com/Wei-Shaw/sub2api/internal/server/middleware"
+	"github.com/Wei-Shaw/sub2api/internal/service"
+)
+
+// CodexModels serves the Codex models manifest for Codex clients.
+//
+// Codex CLI and the Codex desktop app refresh their model picker from
+// GET {base_url}/models?client_version=... (custom provider mode) or
+// GET /backend-api/codex/models (chatgpt_base_url mode). Both routes land
+// here. The manifest is proxied verbatim from the ChatGPT backend with a
+// schedulable OAuth account's credentials, so clients pointed at the gateway
+// see the account's real, always-current model entitlements instead of a
+// frozen local cache.
+func (h *OpenAIGatewayHandler) CodexModels(c *gin.Context) {
+	apiKey, ok := middleware2.GetAPIKeyFromContext(c)
+	if !ok || apiKey.Group == nil {
+		h.errorResponse(c, http.StatusUnauthorized, "invalid_request_error", "API key group is required")
+		return
+	}
+	if apiKey.Group.Platform != service.PlatformOpenAI {
+		h.errorResponse(c, http.StatusNotFound, "not_found_error", "Codex models manifest is only available for OpenAI groups")
+		return
+	}
+
+	account, err := h.gatewayService.SelectAccountForModel(c.Request.Context(), apiKey.GroupID, "", "")
+	if err != nil {
+		h.errorResponse(c, http.StatusServiceUnavailable, "upstream_error", "No available OpenAI accounts")
+		return
+	}
+
+	manifest, err := h.gatewayService.FetchCodexModelsManifest(c.Request.Context(), account, c.Query("client_version"), c.GetHeader("If-None-Match"))
+	if err != nil {
+		h.errorResponse(c, infraerrors.Code(err), "upstream_error", infraerrors.Message(err))
+		return
+	}
+
+	if manifest.ETag != "" {
+		c.Header("ETag", manifest.ETag)
+	}
+	if manifest.NotModified {
+		c.Status(http.StatusNotModified)
+		return
+	}
+	c.Data(http.StatusOK, "application/json", manifest.Body)
+}
diff --git a/backend/internal/server/routes/gateway.go b/backend/internal/server/routes/gateway.go
index d22e339c75..ba5b4f61d1 100644
--- a/backend/internal/server/routes/gateway.go
+++ b/backend/internal/server/routes/gateway.go
@@ -121,7 +121,16 @@ func RegisterGatewayRoutes(
 			}
 			h.Gateway.CountTokens(c)
 		})
-		gateway.GET("/models", h.Gateway.Models)
+		// Codex CLI / Codex app refresh their model picker from the provider's
+		// /models endpoint with a client_version query and expect the ChatGPT
+		// Codex manifest format; other clients keep the OpenAI-style list.
+		gateway.GET("/models", func(c *gin.Context) {
+			if isOpenAIGatewayPlatform(c) && c.Query("client_version") != "" {
+				h.OpenAIGateway.CodexModels(c)
+				return
+			}
+			h.Gateway.Models(c)
+		})
 		gateway.GET("/usage", h.Gateway.Usage)
 		// OpenAI Responses API: auto-route based on group platform
 		gateway.POST("/responses", func(c *gin.Context) {
@@ -214,6 +223,7 @@ func RegisterGatewayRoutes(
 		codexDirect.GET("/responses", func(c *gin.Context) {
 			h.OpenAIGateway.ResponsesWebSocket(c)
 		})
+		codexDirect.GET("/models", h.OpenAIGateway.CodexModels)
 	}
 	// OpenAI Chat Completions API（不带v1前缀的别名）— auto-route based on group platform
 	r.POST("/chat/completions", bodyLimit, clientRequestID, opsErrorLogger, endpointNorm, gin.HandlerFunc(apiKeyAuth), requireGroupAnthropic, func(c *gin.Context) {
diff --git a/backend/internal/server/routes/gateway_codex_models_test.go b/backend/internal/server/routes/gateway_codex_models_test.go
new file mode 100644
index 0000000000..74af755919
--- /dev/null
+++ b/backend/internal/server/routes/gateway_codex_models_test.go
@@ -0,0 +1,22 @@
+package routes
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGatewayRoutesCodexModelsManifestPathIsRegistered(t *testing.T) {
+	router := newGatewayRoutesTestRouter()
+
+	registered := make(map[string]bool)
+	for _, route := range router.Routes() {
+		if route.Method == http.MethodGet {
+			registered[route.Path] = true
+		}
+	}
+
+	require.True(t, registered["/backend-api/codex/models"], "GET /backend-api/codex/models should be registered")
+	require.True(t, registered["/v1/models"], "GET /v1/models should be registered")
+}
diff --git a/backend/internal/service/openai_codex_models_service.go b/backend/internal/service/openai_codex_models_service.go
new file mode 100644
index 0000000000..8a919fa2b0
--- /dev/null
+++ b/backend/internal/service/openai_codex_models_service.go
@@ -0,0 +1,107 @@
+package service
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/httpclient"
+)
+
+// chatgptCodexModelsURL is the ChatGPT Codex models manifest endpoint.
+// Package-level variable so tests can point it at a stub server.
+var chatgptCodexModelsURL = "https://chatgpt.com/backend-api/codex/models"
+
+const codexModelsManifestBodyLimit int64 = 8 << 20
+
+// CodexModelsManifest carries the raw upstream manifest payload plus caching
+// metadata so handlers can pass both through to the client untouched.
+type CodexModelsManifest struct {
+	Body        []byte
+	ETag        string
+	NotModified bool
+}
+
+// FetchCodexModelsManifest fetches the live Codex models manifest from the
+// ChatGPT backend using the account's OAuth credentials.
+//
+// The response body is passed through verbatim: the manifest schema evolves
+// with Codex client releases, and interpreting it here would force the gateway
+// to chase upstream changes. Passing it through keeps the gateway
+// schema-agnostic and always reflects the account's real entitlements.
+func (s *OpenAIGatewayService) FetchCodexModelsManifest(ctx context.Context, account *Account, clientVersion, ifNoneMatch string) (*CodexModelsManifest, error) {
+	if account == nil {
+		return nil, infraerrors.New(http.StatusInternalServerError, "OPENAI_CODEX_MODELS_ACCOUNT_REQUIRED", "account is required")
+	}
+	credAccount, err := resolveCredentialAccount(ctx, s.accountRepo, account)
+	if err != nil {
+		return nil, infraerrors.Newf(http.StatusInternalServerError, "OPENAI_CODEX_MODELS_CREDENTIALS_FAILED", "resolve credential account: %v", err)
+	}
+	accessToken := credAccount.GetOpenAIAccessToken()
+	if accessToken == "" {
+		return nil, infraerrors.New(http.StatusBadGateway, "OPENAI_CODEX_MODELS_TOKEN_MISSING", "account has no Codex backend access token")
+	}
+
+	clientVersion = strings.TrimSpace(clientVersion)
+	if clientVersion == "" {
+		clientVersion = openAICodexProbeVersion
+	}
+	requestURL := chatgptCodexModelsURL + "?client_version=" + url.QueryEscape(clientVersion)
+
+	reqCtx, cancel := context.WithTimeout(ctx, 15*time.Second)
+	defer cancel()
+	req, err := http.NewRequestWithContext(reqCtx, http.MethodGet, requestURL, nil)
+	if err != nil {
+		return nil, infraerrors.Newf(http.StatusInternalServerError, "OPENAI_CODEX_MODELS_REQUEST_FAILED", "create codex models request: %v", err)
+	}
+	req.Header.Set("Authorization", "Bearer "+accessToken)
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("Originator", "codex_cli_rs")
+	req.Header.Set("Version", clientVersion)
+	req.Header.Set("User-Agent", codexCLIUserAgent)
+	if ifNoneMatch = strings.TrimSpace(ifNoneMatch); ifNoneMatch != "" {
+		req.Header.Set("If-None-Match", ifNoneMatch)
+	}
+	setOpenAIChatGPTAccountHeaders(req.Header, credAccount)
+
+	proxyURL := ""
+	if account.ProxyID != nil && account.Proxy != nil {
+		proxyURL = account.Proxy.URL()
+	}
+	client, err := httpclient.GetClient(httpclient.Options{
+		ProxyURL:              proxyURL,
+		Timeout:               15 * time.Second,
+		ResponseHeaderTimeout: 10 * time.Second,
+	})
+	if err != nil {
+		return nil, infraerrors.Newf(http.StatusInternalServerError, "OPENAI_CODEX_MODELS_PROXY_INVALID", "invalid proxy configuration: %v", err)
+	}
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, infraerrors.Newf(http.StatusBadGateway, "OPENAI_CODEX_MODELS_UPSTREAM_FAILED", "codex models manifest request failed: %v", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode == http.StatusNotModified {
+		return &CodexModelsManifest{ETag: resp.Header.Get("ETag"), NotModified: true}, nil
+	}
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
+		message := strings.TrimSpace(string(body))
+		if message == "" {
+			message = resp.Status
+		}
+		return nil, infraerrors.Newf(http.StatusBadGateway, "OPENAI_CODEX_MODELS_UPSTREAM_FAILED", "codex models manifest upstream error %d: %s", resp.StatusCode, message)
+	}
+
+	body, err := io.ReadAll(io.LimitReader(resp.Body, codexModelsManifestBodyLimit))
+	if err != nil {
+		return nil, infraerrors.Newf(http.StatusBadGateway, "OPENAI_CODEX_MODELS_UPSTREAM_FAILED", "read codex models manifest response: %v", err)
+	}
+	return &CodexModelsManifest{Body: body, ETag: resp.Header.Get("ETag")}, nil
+}
diff --git a/backend/internal/service/openai_codex_models_service_test.go b/backend/internal/service/openai_codex_models_service_test.go
new file mode 100644
index 0000000000..c9eae35629
--- /dev/null
+++ b/backend/internal/service/openai_codex_models_service_test.go
@@ -0,0 +1,138 @@
+package service
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func newCodexModelsTestAccount() *Account {
+	return &Account{
+		ID:       1,
+		Platform: PlatformOpenAI,
+		Type:     AccountTypeOAuth,
+		Credentials: map[string]any{
+			"access_token":       "test-access-token",
+			"chatgpt_account_id": "acc-123",
+		},
+	}
+}
+
+func TestFetchCodexModelsManifestPassthrough(t *testing.T) {
+	manifestBody := `{"models":[{"slug":"gpt-5.5","display_name":"GPT-5.5"}]}`
+
+	var gotAuth, gotAccountID, gotOriginator, gotClientVersion string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotAuth = r.Header.Get("Authorization")
+		gotAccountID = r.Header.Get("chatgpt-account-id")
+		gotOriginator = r.Header.Get("Originator")
+		gotClientVersion = r.URL.Query().Get("client_version")
+		w.Header().Set("ETag", `W/"abc123"`)
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(manifestBody))
+	}))
+	defer server.Close()
+
+	original := chatgptCodexModelsURL
+	chatgptCodexModelsURL = server.URL
+	defer func() { chatgptCodexModelsURL = original }()
+
+	s := &OpenAIGatewayService{}
+	manifest, err := s.FetchCodexModelsManifest(context.Background(), newCodexModelsTestAccount(), "0.137.0", "")
+	if err != nil {
+		t.Fatalf("FetchCodexModelsManifest returned error: %v", err)
+	}
+
+	if string(manifest.Body) != manifestBody {
+		t.Errorf("body not passed through verbatim: got %q", manifest.Body)
+	}
+	if manifest.ETag != `W/"abc123"` {
+		t.Errorf("etag not passed through: got %q", manifest.ETag)
+	}
+	if gotAuth != "Bearer test-access-token" {
+		t.Errorf("authorization header: got %q", gotAuth)
+	}
+	if gotAccountID != "acc-123" {
+		t.Errorf("chatgpt-account-id header: got %q", gotAccountID)
+	}
+	if gotOriginator != "codex_cli_rs" {
+		t.Errorf("originator header: got %q", gotOriginator)
+	}
+	if gotClientVersion != "0.137.0" {
+		t.Errorf("client_version query: got %q", gotClientVersion)
+	}
+}
+
+func TestFetchCodexModelsManifestDefaultClientVersion(t *testing.T) {
+	var gotClientVersion string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotClientVersion = r.URL.Query().Get("client_version")
+		_, _ = w.Write([]byte(`{"models":[]}`))
+	}))
+	defer server.Close()
+
+	original := chatgptCodexModelsURL
+	chatgptCodexModelsURL = server.URL
+	defer func() { chatgptCodexModelsURL = original }()
+
+	s := &OpenAIGatewayService{}
+	if _, err := s.FetchCodexModelsManifest(context.Background(), newCodexModelsTestAccount(), "", ""); err != nil {
+		t.Fatalf("FetchCodexModelsManifest returned error: %v", err)
+	}
+	if gotClientVersion != openAICodexProbeVersion {
+		t.Errorf("default client_version: got %q, want %q", gotClientVersion, openAICodexProbeVersion)
+	}
+}
+
+func TestFetchCodexModelsManifestNotModified(t *testing.T) {
+	var gotIfNoneMatch string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotIfNoneMatch = r.Header.Get("If-None-Match")
+		w.Header().Set("ETag", `W/"abc123"`)
+		w.WriteHeader(http.StatusNotModified)
+	}))
+	defer server.Close()
+
+	original := chatgptCodexModelsURL
+	chatgptCodexModelsURL = server.URL
+	defer func() { chatgptCodexModelsURL = original }()
+
+	s := &OpenAIGatewayService{}
+	manifest, err := s.FetchCodexModelsManifest(context.Background(), newCodexModelsTestAccount(), "0.137.0", `W/"abc123"`)
+	if err != nil {
+		t.Fatalf("FetchCodexModelsManifest returned error: %v", err)
+	}
+	if !manifest.NotModified {
+		t.Error("expected NotModified to be true")
+	}
+	if gotIfNoneMatch != `W/"abc123"` {
+		t.Errorf("if-none-match header: got %q", gotIfNoneMatch)
+	}
+}
+
+func TestFetchCodexModelsManifestUpstreamError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, `{"detail":"boom"}`, http.StatusInternalServerError)
+	}))
+	defer server.Close()
+
+	original := chatgptCodexModelsURL
+	chatgptCodexModelsURL = server.URL
+	defer func() { chatgptCodexModelsURL = original }()
+
+	s := &OpenAIGatewayService{}
+	if _, err := s.FetchCodexModelsManifest(context.Background(), newCodexModelsTestAccount(), "0.137.0", ""); err == nil {
+		t.Fatal("expected error for upstream 500, got nil")
+	}
+}
+
+func TestFetchCodexModelsManifestMissingToken(t *testing.T) {
+	account := newCodexModelsTestAccount()
+	delete(account.Credentials, "access_token")
+
+	s := &OpenAIGatewayService{}
+	if _, err := s.FetchCodexModelsManifest(context.Background(), account, "0.137.0", ""); err == nil {
+		t.Fatal("expected error for missing access token, got nil")
+	}
+}