diff --git a/config.example.yaml b/config.example.yaml
index be84de3b5..bb9307cc6 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -119,7 +119,7 @@ routing:
   strategy: "round-robin" # round-robin (default), fill-first
   # Enable universal session-sticky routing for all clients.
   # Session IDs are extracted from: metadata.user_id (Claude Code session format),
-  # X-Session-ID, X-Amp-Thread-Id (Amp CLI),
+  # X-Session-ID, Session_id (Codex), X-Amp-Thread-Id (Amp CLI),
   # X-Client-Request-Id (PI), conversation_id, or first few messages hash.
   # Automatic failover is always enabled when bound auth becomes unavailable.
   session-affinity: false # default: false
diff --git a/internal/config/config.go b/internal/config/config.go
index 7c660cd23..0e1939388 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -237,7 +237,7 @@ type RoutingConfig struct {
 
 	// SessionAffinity enables universal session-sticky routing for all clients.
 	// Session IDs are extracted from multiple sources:
-	// metadata.user_id (Claude Code session format), X-Session-ID,
+	// metadata.user_id (Claude Code session format), X-Session-ID, Session_id (Codex),
 	// X-Amp-Thread-Id (Amp CLI thread), X-Client-Request-Id (PI), metadata.user_id,
 	// conversation_id, or message hash.
 	// Automatic failover is always enabled when bound auth becomes unavailable.
diff --git a/internal/runtime/executor/codex_executor.go b/internal/runtime/executor/codex_executor.go
index c7dd2d3ec..26f2327e6 100644
--- a/internal/runtime/executor/codex_executor.go
+++ b/internal/runtime/executor/codex_executor.go
@@ -931,6 +931,9 @@ func (e *CodexExecutor) cacheHelper(ctx context.Context, from sdktranslator.Form
 	if err != nil {
 		return nil, nil, codexIdentityConfuseState{}, err
 	}
+	if cache.ID != "" {
+		httpReq.Header.Set("Session_id", cache.ID)
+	}
 	return httpReq, rawJSON, identityState, nil
 }
 
@@ -964,7 +967,6 @@ func applyCodexIdentityConfuseHeaders(headers http.Header, state *codexIdentityC
 	if headers == nil {
 		return
 	}
-	defer deleteDeprecatedCodexConversationHeader(headers)
 	if state == nil || !state.enabled {
 		return
 	}
@@ -977,6 +979,12 @@ func applyCodexIdentityConfuseHeaders(headers http.Header, state *codexIdentityC
 	}
 
 	setHeaderCasePreserved(headers, "Session-Id", state.promptCacheKey)
+	if headerValueCaseInsensitive(headers, "session_id") != "" {
+		setHeaderCasePreserved(headers, "session_id", state.promptCacheKey)
+	}
+	if headerValueCaseInsensitive(headers, "Conversation_id") != "" {
+		setHeaderCasePreserved(headers, "Conversation_id", state.promptCacheKey)
+	}
 	headers.Set("X-Client-Request-Id", state.promptCacheKey)
 	headers.Set("Thread-Id", state.promptCacheKey)
 	headers.Set("X-Codex-Window-Id", state.promptCacheKey+":0")
@@ -1072,6 +1080,10 @@ func applyCodexHeaders(r *http.Request, auth *cliproxyauth.Auth, token string, s
 	cfgUserAgent, _ := codexHeaderDefaults(cfg, auth)
 	ensureHeaderWithConfigPrecedence(r.Header, ginHeaders, "User-Agent", cfgUserAgent, codexUserAgent)
 
+	if strings.Contains(r.Header.Get("User-Agent"), "Mac OS") {
+		misc.EnsureHeader(r.Header, ginHeaders, "Session_id", uuid.NewString())
+	}
+
 	if stream {
 		r.Header.Set("Accept", "text/event-stream")
 	} else {
@@ -1090,19 +1102,18 @@ func applyCodexHeaders(r *http.Request, auth *cliproxyauth.Auth, token string, s
 	} else if !isAPIKey {
 		r.Header.Set("Originator", codexOriginator)
 	}
-	// if !isAPIKey {
-	// 	if auth != nil && auth.Metadata != nil {
-	// 		if accountID, ok := auth.Metadata["account_id"].(string); ok {
-	// 			r.Header.Set("Chatgpt-Account-Id", accountID)
-	// 		}
-	// 	}
-	// }
+	if !isAPIKey {
+		if auth != nil && auth.Metadata != nil {
+			if accountID, ok := auth.Metadata["account_id"].(string); ok {
+				r.Header.Set("Chatgpt-Account-Id", accountID)
+			}
+		}
+	}
 	var attrs map[string]string
 	if auth != nil {
 		attrs = auth.Attributes
 	}
 	util.ApplyCustomHeadersFromAttrs(r, attrs)
-	deleteDeprecatedCodexConversationHeader(r.Header)
 }
 
 func newCodexStatusErr(statusCode int, body []byte) statusErr {
diff --git a/internal/runtime/executor/codex_executor_cache_test.go b/internal/runtime/executor/codex_executor_cache_test.go
index 29d244e68..3f7d412ba 100644
--- a/internal/runtime/executor/codex_executor_cache_test.go
+++ b/internal/runtime/executor/codex_executor_cache_test.go
@@ -47,8 +47,8 @@ func TestCodexExecutorCacheHelper_OpenAIChatCompletions_StablePromptCacheKeyFrom
 	if gotConversation := httpReq.Header.Get("Conversation_id"); gotConversation != "" {
 		t.Fatalf("Conversation_id = %q, want empty", gotConversation)
 	}
-	if gotSession := httpReq.Header.Get("Session_id"); gotSession != "" {
-		t.Fatalf("Session_id = %q, want empty", gotSession)
+	if gotSession := httpReq.Header.Get("Session_id"); gotSession != expectedKey {
+		t.Fatalf("Session_id = %q, want %q", gotSession, expectedKey)
 	}
 
 	httpReq2, _, _, err := executor.cacheHelper(ctx, sdktranslator.FromString("openai"), url, nil, req, req.Payload, rawJSON)
@@ -119,8 +119,8 @@ func TestCodexExecutorCacheHelper_IdentityConfuseRemapsBodyAndHeaders(t *testing
 			t.Fatalf("%s = %q, want %q", headerName, gotHeader, expectedPromptCacheKey)
 		}
 	}
-	if gotSession := httpReq.Header.Get("Session_id"); gotSession != "" {
-		t.Fatalf("Session_id = %q, want empty", gotSession)
+	if gotSession := httpReq.Header.Get("Session_id"); gotSession != expectedPromptCacheKey {
+		t.Fatalf("Session_id = %q, want %q", gotSession, expectedPromptCacheKey)
 	}
 	if gotWindow := httpReq.Header.Get("X-Codex-Window-Id"); gotWindow != expectedPromptCacheKey+":0" {
 		t.Fatalf("X-Codex-Window-Id = %q, want %q", gotWindow, expectedPromptCacheKey+":0")
@@ -137,6 +137,20 @@ func TestCodexExecutorCacheHelper_IdentityConfuseRemapsBodyAndHeaders(t *testing
 	}
 }
 
+func TestApplyCodexHeadersUsesAccountHeaderForOAuth(t *testing.T) {
+	httpReq := httptest.NewRequest("POST", "https://example.com/responses", nil)
+	auth := &cliproxyauth.Auth{
+		Provider: "codex",
+		Metadata: map[string]any{"account_id": "acct-1"},
+	}
+
+	applyCodexHeaders(httpReq, auth, "oauth-token", true, nil)
+
+	if got := httpReq.Header.Get("Chatgpt-Account-Id"); got != "acct-1" {
+		t.Fatalf("Chatgpt-Account-Id = %q, want acct-1", got)
+	}
+}
+
 func TestCodexIdentityConfuseKeepsClientBodySeparateFromUpstreamBody(t *testing.T) {
 	cfg := &config.Config{
 		Routing: config.RoutingConfig{Strategy: "fill-first"},
diff --git a/internal/runtime/executor/codex_websockets_executor.go b/internal/runtime/executor/codex_websockets_executor.go
index ecbf21710..2cb9bc98f 100644
--- a/internal/runtime/executor/codex_websockets_executor.go
+++ b/internal/runtime/executor/codex_websockets_executor.go
@@ -857,6 +857,8 @@ func applyCodexPromptCacheHeaders(from sdktranslator.Format, req cliproxyexecuto
 
 	if cache.ID != "" {
 		rawJSON, _ = sjson.SetBytes(rawJSON, "prompt_cache_key", cache.ID)
+		setHeaderCasePreserved(headers, "session_id", cache.ID)
+		headers.Set("Conversation_id", cache.ID)
 	}
 
 	return rawJSON, headers
@@ -897,27 +899,30 @@ func applyCodexWebsocketHeaders(ctx context.Context, headers http.Header, auth *
 		betaHeader = codexResponsesWebsocketBetaHeaderValue
 	}
 	headers.Set("OpenAI-Beta", betaHeader)
+	if strings.Contains(headers.Get("User-Agent"), "Mac OS") {
+		ensureHeaderCasePreserved(headers, ginHeaders, "session_id", "", uuid.NewString())
+	}
+	ensureHeaderCasePreserved(headers, ginHeaders, "session_id", "", "")
 	if originator := strings.TrimSpace(ginHeaders.Get("Originator")); originator != "" {
 		headers.Set("Originator", originator)
 	} else if !isAPIKey {
 		headers.Set("Originator", codexOriginator)
 	}
-	// if !isAPIKey {
-	// 	if auth != nil && auth.Metadata != nil {
-	// 		if accountID, ok := auth.Metadata["account_id"].(string); ok {
-	// 			if trimmed := strings.TrimSpace(accountID); trimmed != "" {
-	// 				setHeaderCasePreserved(headers, "ChatGPT-Account-ID", trimmed)
-	// 			}
-	// 		}
-	// 	}
-	// }
+	if !isAPIKey {
+		if auth != nil && auth.Metadata != nil {
+			if accountID, ok := auth.Metadata["account_id"].(string); ok {
+				if trimmed := strings.TrimSpace(accountID); trimmed != "" {
+					setHeaderCasePreserved(headers, "ChatGPT-Account-ID", trimmed)
+				}
+			}
+		}
+	}
 
 	var attrs map[string]string
 	if auth != nil {
 		attrs = auth.Attributes
 	}
 	util.ApplyCustomHeadersFromAttrs(&http.Request{Header: headers}, attrs)
-	deleteDeprecatedCodexConversationHeader(headers)
 
 	return headers
 }
@@ -993,10 +998,6 @@ func deleteHeaderCaseInsensitive(headers http.Header, key string) {
 	}
 }
 
-func deleteDeprecatedCodexConversationHeader(headers http.Header) {
-	deleteHeaderCaseInsensitive(headers, "Conversation_id")
-}
-
 func codexHeaderDefaults(cfg *config.Config, auth *cliproxyauth.Auth) (string, string) {
 	if cfg == nil || auth == nil {
 		return "", ""
diff --git a/internal/runtime/executor/codex_websockets_executor_test.go b/internal/runtime/executor/codex_websockets_executor_test.go
index ba01d2b66..5dbfbce94 100644
--- a/internal/runtime/executor/codex_websockets_executor_test.go
+++ b/internal/runtime/executor/codex_websockets_executor_test.go
@@ -217,8 +217,11 @@ func TestApplyCodexWebsocketHeadersPassesThroughClientIdentityHeaders(t *testing
 	if got := headers.Get("X-Client-Request-Id"); got != "019d2233-e240-7162-992d-38df0a2a0e0d" {
 		t.Fatalf("X-Client-Request-Id = %s, want %s", got, "019d2233-e240-7162-992d-38df0a2a0e0d")
 	}
-	if got := headerValueCaseInsensitive(headers, "session_id"); got != "" {
-		t.Fatalf("session_id = %q, want empty", got)
+	if got := headerValueCaseInsensitive(headers, "session_id"); got != "legacy-session" {
+		t.Fatalf("session_id = %s, want legacy-session", got)
+	}
+	if _, ok := headers["session_id"]; !ok {
+		t.Fatalf("expected lowercase session_id header key, got %#v", headers)
 	}
 }
 
@@ -341,16 +344,36 @@ func TestApplyCodexWebsocketHeadersPreservesExplicitAPIKeyUserAgent(t *testing.T
 	}
 }
 
-func TestApplyCodexPromptCacheHeadersDoesNotSetDeprecatedConversationHeader(t *testing.T) {
+func TestApplyCodexWebsocketHeadersUsesCanonicalAccountHeader(t *testing.T) {
+	auth := &cliproxyauth.Auth{Provider: "codex", Metadata: map[string]any{"account_id": "acct-1"}}
+
+	headers := applyCodexWebsocketHeaders(context.Background(), http.Header{}, auth, "", nil)
+
+	if got := headerValueCaseInsensitive(headers, "ChatGPT-Account-ID"); got != "acct-1" {
+		t.Fatalf("ChatGPT-Account-ID = %s, want acct-1", got)
+	}
+	values, ok := headers["ChatGPT-Account-ID"]
+	if !ok {
+		t.Fatalf("expected exact ChatGPT-Account-ID key, got %#v", headers)
+	}
+	if len(values) != 1 || values[0] != "acct-1" {
+		t.Fatalf("ChatGPT-Account-ID values = %#v, want [acct-1]", values)
+	}
+}
+
+func TestApplyCodexPromptCacheHeadersSetsLowercaseSessionAndLegacyConversation(t *testing.T) {
 	req := cliproxyexecutor.Request{Model: "gpt-5-codex", Payload: []byte(`{"prompt_cache_key":"cache-1"}`)}
 
 	_, headers := applyCodexPromptCacheHeaders("openai-response", req, []byte(`{"model":"gpt-5-codex"}`))
 
-	if got := headerValueCaseInsensitive(headers, "session_id"); got != "" {
-		t.Fatalf("session_id = %q, want empty", got)
+	if got := headerValueCaseInsensitive(headers, "session_id"); got != "cache-1" {
+		t.Fatalf("session_id = %s, want cache-1", got)
 	}
-	if got := headers.Get("Conversation_id"); got != "" {
-		t.Fatalf("Conversation_id = %q, want empty", got)
+	if _, ok := headers["session_id"]; !ok {
+		t.Fatalf("expected lowercase session_id key, got %#v", headers)
+	}
+	if got := headers.Get("Conversation_id"); got != "cache-1" {
+		t.Fatalf("Conversation_id = %s, want cache-1", got)
 	}
 }
 
@@ -379,8 +402,8 @@ func TestApplyCodexWebsocketHeadersIdentityConfuseRemapsPromptCacheKey(t *testin
 	if gotKey := gjson.GetBytes(body, "prompt_cache_key").String(); gotKey != expectedPromptCacheKey {
 		t.Fatalf("prompt_cache_key = %q, want %q", gotKey, expectedPromptCacheKey)
 	}
-	if gotSession := headerValueCaseInsensitive(headers, "session_id"); gotSession != "" {
-		t.Fatalf("session_id = %q, want empty", gotSession)
+	if gotSession := headerValueCaseInsensitive(headers, "session_id"); gotSession != expectedPromptCacheKey {
+		t.Fatalf("session_id = %q, want %q", gotSession, expectedPromptCacheKey)
 	}
 	if gotRequestID := headers.Get("X-Client-Request-Id"); gotRequestID != expectedPromptCacheKey {
 		t.Fatalf("X-Client-Request-Id = %q, want %q", gotRequestID, expectedPromptCacheKey)
@@ -388,8 +411,8 @@ func TestApplyCodexWebsocketHeadersIdentityConfuseRemapsPromptCacheKey(t *testin
 	if gotThreadID := headers.Get("Thread-Id"); gotThreadID != expectedPromptCacheKey {
 		t.Fatalf("Thread-Id = %q, want %q", gotThreadID, expectedPromptCacheKey)
 	}
-	if gotConversation := headers.Get("Conversation_id"); gotConversation != "" {
-		t.Fatalf("Conversation_id = %q, want empty", gotConversation)
+	if gotConversation := headers.Get("Conversation_id"); gotConversation != expectedPromptCacheKey {
+		t.Fatalf("Conversation_id = %q, want %q", gotConversation, expectedPromptCacheKey)
 	}
 	if gotWindowID := headers.Get("X-Codex-Window-Id"); gotWindowID != expectedPromptCacheKey+":0" {
 		t.Fatalf("X-Codex-Window-Id = %q, want %q", gotWindowID, expectedPromptCacheKey+":0")
diff --git a/sdk/api/handlers/openai/openai_responses_websocket_toolcall_repair.go b/sdk/api/handlers/openai/openai_responses_websocket_toolcall_repair.go
index 6e1e7a673..dc3857b26 100644
--- a/sdk/api/handlers/openai/openai_responses_websocket_toolcall_repair.go
+++ b/sdk/api/handlers/openai/openai_responses_websocket_toolcall_repair.go
@@ -147,6 +147,12 @@ func websocketDownstreamSessionKey(req *http.Request) string {
 			return sessionID
 		}
 	}
+	if sessionID := strings.TrimSpace(req.Header.Get("Session-Id")); sessionID != "" {
+		return sessionID
+	}
+	if sessionID := strings.TrimSpace(req.Header.Get("Session_id")); sessionID != "" {
+		return sessionID
+	}
 	return ""
 }
 
diff --git a/sdk/cliproxy/auth/selector.go b/sdk/cliproxy/auth/selector.go
index 3cf11cf14..19d1843fe 100644
--- a/sdk/cliproxy/auth/selector.go
+++ b/sdk/cliproxy/auth/selector.go
@@ -471,11 +471,12 @@ func NewSessionAffinitySelectorWithConfig(cfg SessionAffinityConfig) *SessionAff
 // Priority for session ID extraction:
 //  1. metadata.user_id (Claude Code format with _session_{uuid}) - highest priority
 //  2. X-Session-ID header
-//  3. X-Amp-Thread-Id header (Amp CLI thread ID)
-//  4. X-Client-Request-Id header (PI)
-//  5. metadata.user_id (non-Claude Code format)
-//  6. conversation_id field in request body
-//  7. Stable hash from first few messages content (fallback)
+//  3. Session_id header (Codex)
+//  4. X-Amp-Thread-Id header (Amp CLI thread ID)
+//  5. X-Client-Request-Id header (PI)
+//  6. metadata.user_id (non-Claude Code format)
+//  7. conversation_id field in request body
+//  8. Stable hash from first few messages content (fallback)
 //
 // Note: The cache key includes provider, session ID, and model to handle cases where
 // a session uses multiple models (e.g., gemini-2.5-pro and gemini-3-flash-preview)
@@ -572,11 +573,12 @@ func (s *SessionAffinitySelector) InvalidateAuth(authID string) {
 // Priority order:
 //  1. metadata.user_id (Claude Code format with _session_{uuid}) - highest priority for Claude Code clients
 //  2. X-Session-ID header
-//  3. X-Amp-Thread-Id header (Amp CLI thread ID)
-//  4. X-Client-Request-Id header (PI)
-//  5. metadata.user_id (non-Claude Code format)
-//  6. conversation_id field in request body
-//  7. Stable hash from first few messages content (fallback)
+//  3. Session_id header (Codex)
+//  4. X-Amp-Thread-Id header (Amp CLI thread ID)
+//  5. X-Client-Request-Id header (PI)
+//  6. metadata.user_id (non-Claude Code format)
+//  7. conversation_id field in request body
+//  8. Stable hash from first few messages content (fallback)
 func ExtractSessionID(headers http.Header, payload []byte, metadata map[string]any) string {
 	primary, _ := extractSessionIDs(headers, payload, metadata)
 	return primary
@@ -612,14 +614,24 @@ func extractSessionIDs(headers http.Header, payload []byte, metadata map[string]
 		}
 	}
 
-	// 3. X-Amp-Thread-Id header (Amp CLI thread ID)
+	// 3. Session_id header (Codex)
+	if headers != nil {
+		if sid := headers.Get("Session-Id"); sid != "" {
+			return "codex:" + sid, ""
+		}
+		if sid := headers.Get("Session_id"); sid != "" {
+			return "codex:" + sid, ""
+		}
+	}
+
+	// 4. X-Amp-Thread-Id header (Amp CLI thread ID)
 	if headers != nil {
 		if tid := headers.Get("X-Amp-Thread-Id"); tid != "" {
 			return "amp:" + tid, ""
 		}
 	}
 
-	// 4. X-Client-Request-Id header (PI)
+	// 5. X-Client-Request-Id header (PI)
 	if headers != nil {
 		if rid := headers.Get("X-Client-Request-Id"); rid != "" {
 			return "clientreq:" + rid, ""
@@ -630,18 +642,18 @@ func extractSessionIDs(headers http.Header, payload []byte, metadata map[string]
 		return "", ""
 	}
 
-	// 5. metadata.user_id (non-Claude Code format)
+	// 6. metadata.user_id (non-Claude Code format)
 	userID := gjson.GetBytes(payload, "metadata.user_id").String()
 	if userID != "" {
 		return "user:" + userID, ""
 	}
 
-	// 6. conversation_id field
+	// 7. conversation_id field
 	if convID := gjson.GetBytes(payload, "conversation_id").String(); convID != "" {
 		return "conv:" + convID, ""
 	}
 
-	// 7. Hash-based fallback from message content
+	// 8. Hash-based fallback from message content
 	return extractMessageHashIDs(payload)
 }
 
diff --git a/sdk/cliproxy/auth/selector_test.go b/sdk/cliproxy/auth/selector_test.go
index 0e2eb9521..99231bdf7 100644
--- a/sdk/cliproxy/auth/selector_test.go
+++ b/sdk/cliproxy/auth/selector_test.go
@@ -776,15 +776,16 @@ func TestExtractSessionID_Headers(t *testing.T) {
 	}
 }
 
-func TestExtractSessionID_IgnoresCodexSessionIDHeader(t *testing.T) {
+func TestExtractSessionID_CodexSessionIDHeader(t *testing.T) {
 	t.Parallel()
 
 	headers := make(http.Header)
 	headers.Set("Session_id", "codex-session-123")
 
 	got := ExtractSessionID(headers, nil, nil)
-	if got != "" {
-		t.Errorf("ExtractSessionID() with deprecated Session_id = %q, want empty", got)
+	want := "codex:codex-session-123"
+	if got != want {
+		t.Errorf("ExtractSessionID() with Session_id = %q, want %q", got, want)
 	}
 }
 
@@ -801,7 +802,7 @@ func TestExtractSessionID_ClientRequestIDHeader(t *testing.T) {
 	}
 }
 
-func TestExtractSessionID_ClientRequestIDIgnoresDeprecatedCodexSessionID(t *testing.T) {
+func TestExtractSessionID_CodexSessionIDPriorityOverClientRequestID(t *testing.T) {
 	t.Parallel()
 
 	headers := make(http.Header)
@@ -809,9 +810,9 @@ func TestExtractSessionID_ClientRequestIDIgnoresDeprecatedCodexSessionID(t *test
 	headers.Set("Session_id", "codex-session-456")
 
 	got := ExtractSessionID(headers, nil, nil)
-	want := "clientreq:pi-session-123"
+	want := "codex:codex-session-456"
 	if got != want {
-		t.Errorf("ExtractSessionID() = %q, want %q (deprecated Session_id should be ignored)", got, want)
+		t.Errorf("ExtractSessionID() = %q, want %q (Session_id should take priority over X-Client-Request-Id)", got, want)
 	}
 }