diff --git a/src/app/v1/_lib/codex/__tests__/session-extractor.test.ts b/src/app/v1/_lib/codex/__tests__/session-extractor.test.ts
new file mode 100644
index 000000000..76f7f67d4
--- /dev/null
+++ b/src/app/v1/_lib/codex/__tests__/session-extractor.test.ts
@@ -0,0 +1,148 @@
+import { describe, expect, test } from "vitest";
+import { extractCodexSessionId, isCodexClient } from "../session-extractor";
+
+describe("Codex session extractor", () => {
+  test("extracts from header session_id", () => {
+    const headerSessionId = "sess_123456789012345678901";
+    const result = extractCodexSessionId(
+      new Headers({ session_id: headerSessionId }),
+      {
+        metadata: { session_id: "sess_aaaaaaaaaaaaaaaaaaaaa" },
+        previous_response_id: "resp_123456789012345678901",
+      },
+      "codex_cli_rs/0.50.0 (Mac OS 26.0.1; arm64)"
+    );
+
+    expect(result.sessionId).toBe(headerSessionId);
+    expect(result.source).toBe("header_session_id");
+  });
+
+  test("extracts from header x-session-id", () => {
+    const headerSessionId = "sess_123456789012345678902";
+    const result = extractCodexSessionId(
+      new Headers({ "x-session-id": headerSessionId }),
+      {
+        metadata: { session_id: "sess_aaaaaaaaaaaaaaaaaaaaa" },
+        previous_response_id: "resp_123456789012345678901",
+      },
+      "codex_cli_rs/0.50.0 (Mac OS 26.0.1; arm64)"
+    );
+
+    expect(result.sessionId).toBe(headerSessionId);
+    expect(result.source).toBe("header_x_session_id");
+  });
+
+  test("extracts from body metadata.session_id", () => {
+    const bodySessionId = "sess_123456789012345678903";
+    const result = extractCodexSessionId(
+      new Headers(),
+      { metadata: { session_id: bodySessionId } },
+      "codex_cli_rs/0.50.0 (Mac OS 26.0.1; arm64)"
+    );
+
+    expect(result.sessionId).toBe(bodySessionId);
+    expect(result.source).toBe("body_metadata_session_id");
+  });
+
+  test("falls back to previous_response_id", () => {
+    const previousResponseId = "resp_123456789012345678901";
+    const result = extractCodexSessionId(
+      new Headers(),
+      { previous_response_id: previousResponseId },
+      "codex_cli_rs/0.50.0 (Mac OS 26.0.1; arm64)"
+    );
+
+    expect(result.sessionId).toBe(`codex_prev_${previousResponseId}`);
+    expect(result.source).toBe("body_previous_response_id");
+  });
+
+  test("rejects previous_response_id that would exceed 256 after prefix", () => {
+    const longId = "a".repeat(250); // 250 + 11 (prefix) = 261 > 256
+    const result = extractCodexSessionId(new Headers(), { previous_response_id: longId }, null);
+    expect(result.sessionId).toBe(null);
+    expect(result.source).toBe(null);
+  });
+
+  test("respects extraction priority", () => {
+    const sessionIdFromHeader = "sess_123456789012345678904";
+    const xSessionIdFromHeader = "sess_123456789012345678905";
+    const sessionIdFromBody = "sess_123456789012345678906";
+    const previousResponseId = "resp_123456789012345678901";
+
+    const result = extractCodexSessionId(
+      new Headers({
+        session_id: sessionIdFromHeader,
+        "x-session-id": xSessionIdFromHeader,
+      }),
+      {
+        metadata: { session_id: sessionIdFromBody },
+        previous_response_id: previousResponseId,
+      },
+      "codex_cli_rs/0.50.0 (Mac OS 26.0.1; arm64)"
+    );
+
+    expect(result.sessionId).toBe(sessionIdFromHeader);
+    expect(result.source).toBe("header_session_id");
+  });
+
+  test("detects Codex client User-Agent", () => {
+    expect(isCodexClient("codex_cli_rs/0.50.0 (Mac OS 26.0.1; arm64)")).toBe(true);
+    expect(isCodexClient("codex_vscode/0.35.0 (Windows 10.0.26100; x86_64)")).toBe(true);
+    expect(isCodexClient("Mozilla/5.0")).toBe(false);
+    expect(isCodexClient(null)).toBe(false);
+  });
+
+  test("rejects session_id shorter than 21 characters", () => {
+    const result = extractCodexSessionId(
+      new Headers({ session_id: "short_id_12345" }), // 14 chars
+      {},
+      null
+    );
+    expect(result.sessionId).toBe(null);
+    expect(result.source).toBe(null);
+  });
+
+  test("accepts session_id with exactly 21 characters (minimum)", () => {
+    const minId = "a".repeat(21);
+    const result = extractCodexSessionId(new Headers({ session_id: minId }), {}, null);
+    expect(result.sessionId).toBe(minId);
+    expect(result.source).toBe("header_session_id");
+  });
+
+  test("accepts session_id with exactly 256 characters (maximum)", () => {
+    const maxId = "a".repeat(256);
+    const result = extractCodexSessionId(new Headers({ session_id: maxId }), {}, null);
+    expect(result.sessionId).toBe(maxId);
+    expect(result.source).toBe("header_session_id");
+  });
+
+  test("rejects session_id longer than 256 characters", () => {
+    const longId = "a".repeat(300);
+    const result = extractCodexSessionId(new Headers({ session_id: longId }), {}, null);
+    expect(result.sessionId).toBe(null);
+    expect(result.source).toBe(null);
+  });
+
+  test("rejects session_id with invalid characters", () => {
+    // Test with body metadata to avoid Headers normalization
+    const result = extractCodexSessionId(
+      new Headers(),
+      { metadata: { session_id: "sess_123456789@#$%^&*()!" } },
+      null
+    );
+    expect(result.sessionId).toBe(null);
+  });
+
+  test("accepts session_id with allowed special characters", () => {
+    const validId = "sess-123_456.789:abc012345";
+    const result = extractCodexSessionId(new Headers({ session_id: validId }), {}, null);
+    expect(result.sessionId).toBe(validId);
+  });
+
+  test("returns null when no valid session_id found", () => {
+    const result = extractCodexSessionId(new Headers(), {}, "codex_cli_rs/0.50.0");
+    expect(result.sessionId).toBe(null);
+    expect(result.source).toBe(null);
+    expect(result.isCodexClient).toBe(true);
+  });
+});
diff --git a/src/app/v1/_lib/codex/session-extractor.ts b/src/app/v1/_lib/codex/session-extractor.ts
new file mode 100644
index 000000000..6a82d064f
--- /dev/null
+++ b/src/app/v1/_lib/codex/session-extractor.ts
@@ -0,0 +1,112 @@
+import "server-only";
+
+export type CodexSessionIdSource =
+  | "header_session_id"
+  | "header_x_session_id"
+  | "body_metadata_session_id"
+  | "body_previous_response_id"
+  | null;
+
+export interface CodexSessionExtractionResult {
+  sessionId: string | null;
+  source: CodexSessionIdSource;
+  isCodexClient: boolean;
+}
+
+// Session ID validation constants
+const CODEX_SESSION_ID_MIN_LENGTH = 21; // Codex session_id typically > 20 chars (UUID-like)
+const CODEX_SESSION_ID_MAX_LENGTH = 256; // Prevent Redis key bloat from malicious input
+const SESSION_ID_PATTERN = /^[\w\-.:]+$/; // Alphanumeric, dash, dot, colon only
+
+// Codex CLI User-Agent pattern (pre-compiled for performance)
+const CODEX_CLI_PATTERN = /^(codex_vscode|codex_cli_rs)\/[\d.]+/i;
+
+export function normalizeCodexSessionId(value: unknown): string | null {
+  if (typeof value !== "string") return null;
+
+  const trimmed = value.trim();
+  if (!trimmed) return null;
+
+  if (trimmed.length < CODEX_SESSION_ID_MIN_LENGTH) return null;
+  if (trimmed.length > CODEX_SESSION_ID_MAX_LENGTH) return null;
+  if (!SESSION_ID_PATTERN.test(trimmed)) return null;
+
+  return trimmed;
+}
+
+function parseMetadata(requestBody: Record<string, unknown>): Record<string, unknown> | null {
+  const metadata = requestBody.metadata;
+  if (!metadata || typeof metadata !== "object" || Array.isArray(metadata)) return null;
+  return metadata as Record<string, unknown>;
+}
+
+/**
+ * Detect official Codex CLI clients by User-Agent.
+ *
+ * Examples:
+ * - codex_vscode/0.35.0 (...)
+ * - codex_cli_rs/0.50.0 (...)
+ */
+export function isCodexClient(userAgent: string | null): boolean {
+  if (!userAgent) return false;
+  return CODEX_CLI_PATTERN.test(userAgent);
+}
+
+/**
+ * Extract Codex session id from headers/body with priority:
+ * 1) headers["session_id"]
+ * 2) headers["x-session-id"]
+ * 3) body.metadata.session_id
+ * 4) body.previous_response_id (fallback, prefixed with "codex_prev_")
+ *
+ * Only accept session ids with length > 20.
+ */
+export function extractCodexSessionId(
+  headers: Headers,
+  requestBody: Record<string, unknown>,
+  userAgent: string | null
+): CodexSessionExtractionResult {
+  const officialClient = isCodexClient(userAgent);
+
+  const headerSessionId = normalizeCodexSessionId(headers.get("session_id"));
+  if (headerSessionId) {
+    return {
+      sessionId: headerSessionId,
+      source: "header_session_id",
+      isCodexClient: officialClient,
+    };
+  }
+
+  const headerXSessionId = normalizeCodexSessionId(headers.get("x-session-id"));
+  if (headerXSessionId) {
+    return {
+      sessionId: headerXSessionId,
+      source: "header_x_session_id",
+      isCodexClient: officialClient,
+    };
+  }
+
+  const metadata = parseMetadata(requestBody);
+  const bodyMetadataSessionId = metadata ? normalizeCodexSessionId(metadata.session_id) : null;
+  if (bodyMetadataSessionId) {
+    return {
+      sessionId: bodyMetadataSessionId,
+      source: "body_metadata_session_id",
+      isCodexClient: officialClient,
+    };
+  }
+
+  const prevResponseId = normalizeCodexSessionId(requestBody.previous_response_id);
+  if (prevResponseId) {
+    const sessionId = `codex_prev_${prevResponseId}`;
+    if (sessionId.length <= CODEX_SESSION_ID_MAX_LENGTH) {
+      return {
+        sessionId,
+        source: "body_previous_response_id",
+        isCodexClient: officialClient,
+      };
+    }
+  }
+
+  return { sessionId: null, source: null, isCodexClient: officialClient };
+}
diff --git a/src/app/v1/_lib/converters/codex-to-claude/request.ts b/src/app/v1/_lib/converters/codex-to-claude/request.ts
index 3cc024215..1e28ed56e 100644
--- a/src/app/v1/_lib/converters/codex-to-claude/request.ts
+++ b/src/app/v1/_lib/converters/codex-to-claude/request.ts
@@ -18,6 +18,7 @@
  */
 
 import { randomBytes } from "node:crypto";
+import { normalizeCodexSessionId } from "@/app/v1/_lib/codex/session-extractor";
 import { logger } from "@/lib/logger";
 
 /**
@@ -26,6 +27,7 @@ import { logger } from "@/lib/logger";
 interface ResponseAPIRequest {
   model?: string;
   instructions?: string;
+  metadata?: Record<string, unknown>;
   input?: Array<{
     type?: string;
     role?: string;
@@ -115,7 +117,12 @@ function generateToolCallID(): string {
 /**
  * 生成用户 ID（基于 account 和 session）
  */
-function generateUserID(): string {
+function generateUserID(originalMetadata?: Record<string, unknown>): string {
+  const sessionId = normalizeCodexSessionId(originalMetadata?.session_id);
+  if (sessionId) {
+    return `codex_session_${sessionId}`;
+  }
+
   // 简化实现：使用随机 UUID
   const account = randomBytes(16).toString("hex");
   const session = randomBytes(16).toString("hex");
@@ -144,7 +151,7 @@ export function transformCodexRequestToClaude(
     max_tokens: 32000,
     messages: [],
     metadata: {
-      user_id: generateUserID(),
+      user_id: generateUserID(req.metadata),
     },
     stream,
   };
diff --git a/src/app/v1/_lib/proxy/session-guard.ts b/src/app/v1/_lib/proxy/session-guard.ts
index 0e0889cce..7acd1a795 100644
--- a/src/app/v1/_lib/proxy/session-guard.ts
+++ b/src/app/v1/_lib/proxy/session-guard.ts
@@ -48,8 +48,11 @@ export class ProxySessionGuard {
     try {
       // 1. 尝试从客户端提取 session_id（metadata.session_id）
       const clientSessionId =
-        SessionManager.extractClientSessionId(session.request.message) ||
-        session.generateDeterministicSessionId();
+        SessionManager.extractClientSessionId(
+          session.request.message,
+          session.headers,
+          session.userAgent
+        ) || session.generateDeterministicSessionId();
 
       // 2. 获取 messages 数组
       const messages = session.getMessages();
diff --git a/src/lib/session-manager.ts b/src/lib/session-manager.ts
index 730e6a397..a58c43bf4 100644
--- a/src/lib/session-manager.ts
+++ b/src/lib/session-manager.ts
@@ -1,6 +1,7 @@
 import "server-only";
 
 import crypto from "node:crypto";
+import { extractCodexSessionId } from "@/app/v1/_lib/codex/session-extractor";
 import { sanitizeHeaders } from "@/app/v1/_lib/proxy/errors";
 import { logger } from "@/lib/logger";
 import { normalizeRequestSequence } from "@/lib/utils/request-sequence";
@@ -82,7 +83,26 @@ export class SessionManager {
    * 1. metadata.user_id (Claude Code 主要方式，格式: "{user}_session_{sessionId}")
    * 2. metadata.session_id (备选方式)
    */
-  static extractClientSessionId(requestMessage: Record<string, unknown>): string | null {
+  static extractClientSessionId(
+    requestMessage: Record<string, unknown>,
+    headers?: Headers | null,
+    userAgent?: string | null
+  ): string | null {
+    // Codex 请求：优先尝试从 headers/body 提取稳定的 session_id
+    if (headers && Array.isArray(requestMessage.input)) {
+      const result = extractCodexSessionId(headers, requestMessage, userAgent ?? null);
+      if (result.sessionId) {
+        logger.trace("SessionManager: Extracted session from Codex request", {
+          sessionId: result.sessionId,
+          source: result.source,
+          isCodexClient: result.isCodexClient,
+        });
+        return result.sessionId;
+      }
+
+      return null;
+    }
+
     const metadata = requestMessage.metadata;
     if (!metadata || typeof metadata !== "object") {
       return null;