diff --git a/src/config/types.base.ts b/src/config/types.base.ts
index e7da1ecd8..77d0b3a10 100644
--- a/src/config/types.base.ts
+++ b/src/config/types.base.ts
@@ -76,6 +76,20 @@ export type SessionResetByTypeConfig = {
   thread?: SessionResetConfig;
 };
 
+/** TTL configuration for automatic session cleanup. */
+export type SessionTtlConfig = {
+  /** Idle timeout in seconds. Sessions inactive for this duration are eligible for cleanup. */
+  idle?: number;
+  /** Maximum age in seconds. Sessions older than this are eligible for cleanup regardless of activity. */
+  maxAge?: number;
+};
+
+/** Cleanup service configuration. */
+export type SessionCleanupConfig = {
+  /** Interval between cleanup runs in seconds. Default: 300 (5 minutes). */
+  intervalSeconds?: number;
+};
+
 export type SessionConfig = {
   scope?: SessionScope;
   /** DM session scoping (default: "main"). */
@@ -97,6 +111,10 @@ export type SessionConfig = {
     /** Max ping-pong turns between requester/target (0–5). Default: 5. */
     maxPingPongTurns?: number;
   };
+  /** TTL for automatic session cleanup. Can be a number (idle seconds) or an object with idle/maxAge. */
+  ttl?: number | SessionTtlConfig;
+  /** Configuration for the automatic cleanup service. */
+  cleanup?: SessionCleanupConfig;
 };
 
 export type LoggingConfig = {
diff --git a/src/config/zod-schema.session.ts b/src/config/zod-schema.session.ts
index 4412f5515..d1c4f6fb0 100644
--- a/src/config/zod-schema.session.ts
+++ b/src/config/zod-schema.session.ts
@@ -16,6 +16,22 @@ const SessionResetConfigSchema = z
   })
   .strict();
 
+const SessionTtlSchema = z.union([
+  z.number().int().positive(), // Simple form: just seconds
+  z
+    .object({
+      idle: z.number().int().positive().optional(),
+      maxAge: z.number().int().positive().optional(),
+    })
+    .strict(),
+]);
+
+const SessionCleanupSchema = z
+  .object({
+    intervalSeconds: z.number().int().positive().optional(),
+  })
+  .strict();
+
 export const SessionSchema = z
   .object({
     scope: z.union([z.literal("per-sender"), z.literal("global")]).optional(),
@@ -82,6 +98,8 @@ export const SessionSchema = z
       })
       .strict()
       .optional(),
+    ttl: SessionTtlSchema.optional(),
+    cleanup: SessionCleanupSchema.optional(),
   })
   .strict()
   .optional();
diff --git a/src/gateway/session-cleanup.ts b/src/gateway/session-cleanup.ts
new file mode 100644
index 000000000..e6ccb3b89
--- /dev/null
+++ b/src/gateway/session-cleanup.ts
@@ -0,0 +1,129 @@
+/**
+ * Session cleanup service for automatic TTL-based session removal.
+ * @module session-cleanup
+ * @see https://github.com/moltbot/moltbot/issues/3250
+ */
+
+import { loadConfig } from "../config/index.js";
+import type { MoltbotConfig } from "../config/types.js";
+import { log } from "../logging.js";
+import { loadCombinedSessionStoreForGateway } from "./session-utils.js";
+import {
+  normalizeSessionTtl,
+  getExpiredSessionKeys,
+  getCleanupConfig,
+  DEFAULT_CLEANUP_INTERVAL_SECONDS,
+} from "./session-ttl.js";
+
+let cleanupIntervalId: ReturnType<typeof setInterval> | null = null;
+
+/**
+ * Run a single cleanup pass.
+ * @param cfg - Moltbot configuration
+ * @returns Number of sessions cleaned up
+ */
+export async function runSessionCleanup(cfg: MoltbotConfig): Promise<number> {
+  const sessionConfig = cfg.session;
+  if (!sessionConfig?.ttl) {
+    return 0;
+  }
+
+  const ttl = normalizeSessionTtl(sessionConfig.ttl);
+  if (!ttl) {
+    return 0;
+  }
+
+  const { store } = loadCombinedSessionStoreForGateway(cfg);
+  const expiredKeys = getExpiredSessionKeys(store, ttl);
+
+  if (expiredKeys.length === 0) {
+    return 0;
+  }
+
+  log.info({ count: expiredKeys.length }, "[session-cleanup] Found expired sessions");
+
+  // Delete expired sessions
+  // Note: We import dynamically to avoid circular dependencies
+  const { sessionsHandlers } = await import("./server-methods/sessions.js");
+
+  let cleaned = 0;
+  for (const key of expiredKeys) {
+    try {
+      // Create a mock respond function to track success
+      let success = false;
+      const respond = (ok: boolean) => {
+        success = ok;
+      };
+
+      await sessionsHandlers["sessions.delete"]({
+        params: { key },
+        respond: respond as never,
+        context: {} as never,
+      });
+
+      if (success) {
+        cleaned++;
+        log.debug({ key }, "[session-cleanup] Deleted expired session");
+      }
+    } catch (err) {
+      log.warn({ key, err }, "[session-cleanup] Failed to delete session");
+    }
+  }
+
+  log.info({ cleaned, total: expiredKeys.length }, "[session-cleanup] Cleanup complete");
+  return cleaned;
+}
+
+/**
+ * Start the session cleanup service.
+ * @param cfg - Moltbot configuration
+ */
+export function startSessionCleanupService(cfg: MoltbotConfig): void {
+  if (cleanupIntervalId) {
+    log.debug("[session-cleanup] Service already running");
+    return;
+  }
+
+  const sessionConfig = cfg.session;
+  if (!sessionConfig?.ttl) {
+    log.debug("[session-cleanup] No TTL configured, skipping cleanup service");
+    return;
+  }
+
+  const cleanupConfig = getCleanupConfig(sessionConfig.cleanup);
+  const intervalMs = cleanupConfig.intervalSeconds * 1000;
+
+  log.info(
+    { intervalSeconds: cleanupConfig.intervalSeconds },
+    "[session-cleanup] Starting cleanup service",
+  );
+
+  // Run initial cleanup after a short delay
+  setTimeout(() => {
+    runSessionCleanup(cfg).catch((err) => {
+      log.error({ err }, "[session-cleanup] Initial cleanup failed");
+    });
+  }, 5000);
+
+  // Schedule periodic cleanup
+  cleanupIntervalId = setInterval(() => {
+    // Reload config to pick up any changes
+    const currentCfg = loadConfig();
+    runSessionCleanup(currentCfg).catch((err) => {
+      log.error({ err }, "[session-cleanup] Periodic cleanup failed");
+    });
+  }, intervalMs);
+
+  log.info("[session-cleanup] Cleanup service started");
+}
+
+/**
+ * Stop the session cleanup service.
+ */
+export function stopSessionCleanupService(): void {
+  if (cleanupIntervalId) {
+    clearInterval(cleanupIntervalId);
+    cleanupIntervalId = null;
+    log.info("[session-cleanup] Cleanup service stopped");
+  }
+}
diff --git a/src/gateway/session-ttl.test.ts b/src/gateway/session-ttl.test.ts
new file mode 100644
index 000000000..03968165b
--- /dev/null
+++ b/src/gateway/session-ttl.test.ts
@@ -0,0 +1,151 @@
+/**
+ * Unit tests for session TTL utilities.
+ */
+
+import { describe, it, expect } from "vitest";
+import {
+  normalizeSessionTtl,
+  isSessionExpired,
+  getExpiredSessionKeys,
+  getCleanupConfig,
+  DEFAULT_CLEANUP_INTERVAL_SECONDS,
+} from "./session-ttl.js";
+import type { SessionEntry } from "../config/sessions.js";
+
+describe("session-ttl", () => {
+  describe("normalizeSessionTtl", () => {
+    it("returns undefined for undefined input", () => {
+      expect(normalizeSessionTtl(undefined)).toBeUndefined();
+    });
+
+    it("converts number to idle config", () => {
+      expect(normalizeSessionTtl(3600)).toEqual({ idle: 3600 });
+    });
+
+    it("passes through object form", () => {
+      const ttl = { idle: 3600, maxAge: 86400 };
+      expect(normalizeSessionTtl(ttl)).toEqual(ttl);
+    });
+
+    it("returns undefined for empty object", () => {
+      expect(normalizeSessionTtl({})).toBeUndefined();
+    });
+
+    it("handles object with only idle", () => {
+      expect(normalizeSessionTtl({ idle: 1800 })).toEqual({ idle: 1800 });
+    });
+
+    it("handles object with only maxAge", () => {
+      expect(normalizeSessionTtl({ maxAge: 43200 })).toEqual({ maxAge: 43200 });
+    });
+  });
+
+  describe("isSessionExpired", () => {
+    const now = 1706400000000; // Fixed timestamp for testing
+
+    it("returns false when session is active within idle timeout", () => {
+      const entry: SessionEntry = {
+        sessionId: "test",
+        updatedAt: now - 1000 * 60 * 5, // 5 minutes ago
+      };
+      expect(isSessionExpired(entry, { idle: 3600 }, now)).toBe(false);
+    });
+
+    it("returns true when session is idle beyond timeout", () => {
+      const entry: SessionEntry = {
+        sessionId: "test",
+        updatedAt: now - 1000 * 60 * 70, // 70 minutes ago
+      };
+      expect(isSessionExpired(entry, { idle: 3600 }, now)).toBe(true);
+    });
+
+    it("returns false when session is within maxAge", () => {
+      const entry: SessionEntry = {
+        sessionId: "test",
+        createdAt: now - 1000 * 60 * 60 * 12, // 12 hours ago
+      };
+      expect(isSessionExpired(entry, { maxAge: 86400 }, now)).toBe(false);
+    });
+
+    it("returns true when session exceeds maxAge", () => {
+      const entry: SessionEntry = {
+        sessionId: "test",
+        createdAt: now - 1000 * 60 * 60 * 25, // 25 hours ago
+      };
+      expect(isSessionExpired(entry, { maxAge: 86400 }, now)).toBe(true);
+    });
+
+    it("checks both idle and maxAge", () => {
+      const entry: SessionEntry = {
+        sessionId: "test",
+        createdAt: now - 1000 * 60 * 60 * 20, // 20 hours ago
+        updatedAt: now - 1000 * 60 * 30, // 30 minutes ago (active)
+      };
+      // Active within idle but check maxAge too
+      expect(isSessionExpired(entry, { idle: 3600, maxAge: 86400 }, now)).toBe(false);
+    });
+
+    it("expires on either condition when both set", () => {
+      const entry: SessionEntry = {
+        sessionId: "test",
+        createdAt: now - 1000 * 60 * 60 * 25, // 25 hours ago (exceeds maxAge)
+        updatedAt: now - 1000 * 60 * 30, // 30 minutes ago (within idle)
+      };
+      expect(isSessionExpired(entry, { idle: 3600, maxAge: 86400 }, now)).toBe(true);
+    });
+
+    it("returns false when no timestamps available", () => {
+      const entry: SessionEntry = { sessionId: "test" };
+      expect(isSessionExpired(entry, { idle: 3600, maxAge: 86400 }, now)).toBe(false);
+    });
+  });
+
+  describe("getExpiredSessionKeys", () => {
+    const now = 1706400000000;
+
+    it("returns empty array for empty store", () => {
+      expect(getExpiredSessionKeys({}, { idle: 3600 }, now)).toEqual([]);
+    });
+
+    it("returns empty array when no sessions expired", () => {
+      const store: Record<string, SessionEntry> = {
+        "session:a": { sessionId: "a", updatedAt: now - 1000 * 60 * 5 },
+        "session:b": { sessionId: "b", updatedAt: now - 1000 * 60 * 10 },
+      };
+      expect(getExpiredSessionKeys(store, { idle: 3600 }, now)).toEqual([]);
+    });
+
+    it("returns only expired session keys", () => {
+      const store: Record<string, SessionEntry> = {
+        "session:active": { sessionId: "active", updatedAt: now - 1000 * 60 * 5 },
+        "session:expired": { sessionId: "expired", updatedAt: now - 1000 * 60 * 70 },
+        "session:old": { sessionId: "old", updatedAt: now - 1000 * 60 * 120 },
+      };
+      const expired = getExpiredSessionKeys(store, { idle: 3600 }, now);
+      expect(expired).toContain("session:expired");
+      expect(expired).toContain("session:old");
+      expect(expired).not.toContain("session:active");
+      expect(expired).toHaveLength(2);
+    });
+  });
+
+  describe("getCleanupConfig", () => {
+    it("returns default interval when undefined", () => {
+      expect(getCleanupConfig()).toEqual({
+        intervalSeconds: DEFAULT_CLEANUP_INTERVAL_SECONDS,
+      });
+    });
+
+    it("returns custom interval when set", () => {
+      expect(getCleanupConfig({ intervalSeconds: 600 })).toEqual({
+        intervalSeconds: 600,
+      });
+    });
+
+    it("returns default when empty object", () => {
+      expect(getCleanupConfig({})).toEqual({
+        intervalSeconds: DEFAULT_CLEANUP_INTERVAL_SECONDS,
+      });
+    });
+  });
+});
diff --git a/src/gateway/session-ttl.ts b/src/gateway/session-ttl.ts
new file mode 100644
index 000000000..bf4390af7
--- /dev/null
+++ b/src/gateway/session-ttl.ts
@@ -0,0 +1,98 @@
+/**
+ * Session TTL (Time-To-Live) utilities for automatic session cleanup.
+ * @module session-ttl
+ * @see https://github.com/moltbot/moltbot/issues/3250
+ */
+
+import type { SessionEntry } from "../config/sessions.js";
+import type { SessionTtlConfig, SessionCleanupConfig } from "../config/types.base.js";
+
+/** Default cleanup interval in seconds (5 minutes). */
+export const DEFAULT_CLEANUP_INTERVAL_SECONDS = 300;
+
+/**
+ * Normalize TTL config from number or object form to object form.
+ * @param ttl - TTL config (number for idle seconds, or object with idle/maxAge)
+ * @returns Normalized TTL config object, or undefined if no TTL configured
+ */
+export function normalizeSessionTtl(
+  ttl: number | SessionTtlConfig | undefined,
+): SessionTtlConfig | undefined {
+  if (ttl === undefined) return undefined;
+  if (typeof ttl === "number") {
+    return { idle: ttl };
+  }
+  // Validate at least one TTL option is set
+  if (ttl.idle === undefined && ttl.maxAge === undefined) {
+    return undefined;
+  }
+  return ttl;
+}
+
+/**
+ * Check if a session is expired based on TTL configuration.
+ * @param entry - Session entry to check
+ * @param ttl - TTL configuration
+ * @param now - Current timestamp in ms (default: Date.now())
+ * @returns true if session is expired
+ */
+export function isSessionExpired(
+  entry: SessionEntry,
+  ttl: SessionTtlConfig,
+  now: number = Date.now(),
+): boolean {
+  const updatedAt = entry.updatedAt;
+  const createdAt = entry.createdAt;
+
+  // Check idle timeout
+  if (ttl.idle !== undefined && updatedAt) {
+    const idleMs = ttl.idle * 1000;
+    if (now - updatedAt > idleMs) {
+      return true;
+    }
+  }
+
+  // Check max age
+  if (ttl.maxAge !== undefined && createdAt) {
+    const maxAgeMs = ttl.maxAge * 1000;
+    if (now - createdAt > maxAgeMs) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+/**
+ * Get list of session keys that are expired.
+ * @param store - Session store (key -> entry map)
+ * @param ttl - TTL configuration
+ * @param now - Current timestamp in ms (default: Date.now())
+ * @returns Array of expired session keys
+ */
+export function getExpiredSessionKeys(
+  store: Record<string, SessionEntry>,
+  ttl: SessionTtlConfig,
+  now: number = Date.now(),
+): string[] {
+  const expired: string[] = [];
+
+  for (const [key, entry] of Object.entries(store)) {
+    if (isSessionExpired(entry, ttl, now)) {
+      expired.push(key);
+    }
+  }
+
+  return expired;
+}
+
+/**
+ * Get cleanup configuration with defaults.
+ * @param config - Cleanup config from user
+ * @returns Cleanup config with defaults applied
+ */
+export function getCleanupConfig(config?: SessionCleanupConfig): Required<SessionCleanupConfig> {
+  return {
+    intervalSeconds: config?.intervalSeconds ?? DEFAULT_CLEANUP_INTERVAL_SECONDS,
+  };
+}