diff --git a/src/dao/BearerKeyDao.ts b/src/dao/BearerKeyDao.ts
index 56738e2..812883b 100644
--- a/src/dao/BearerKeyDao.ts
+++ b/src/dao/BearerKeyDao.ts
@@ -24,7 +24,10 @@ export class BearerKeyDaoImpl extends JsonFileBaseDao implements BearerKeyDao {
   private async loadKeysWithMigration(): Promise<BearerKey[]> {
     const settings = await this.loadSettings();
 
-    if (Array.isArray(settings.bearerKeys) && settings.bearerKeys.length > 0) {
+    // Treat an existing array (including an empty array) as already migrated.
+    // Otherwise, when there are no configured keys, we'd rewrite mcp_settings.json
+    // on every request, which also clears the global settings cache.
+    if (Array.isArray(settings.bearerKeys)) {
       return settings.bearerKeys;
     }
 
diff --git a/tests/dao/bearerKeyDao.test.ts b/tests/dao/bearerKeyDao.test.ts
new file mode 100644
index 0000000..be23b6b
--- /dev/null
+++ b/tests/dao/bearerKeyDao.test.ts
@@ -0,0 +1,97 @@
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+
+import { BearerKeyDaoImpl } from '../../src/dao/BearerKeyDao.js';
+
+const writeSettings = (settingsPath: string, settings: unknown): void => {
+  fs.writeFileSync(settingsPath, JSON.stringify(settings, null, 2), 'utf8');
+};
+
+describe('BearerKeyDaoImpl migration + settings caching behavior', () => {
+  let tmpDir: string;
+  let settingsPath: string;
+  let originalSettingsEnv: string | undefined;
+
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'mcphub-bearer-keys-'));
+    settingsPath = path.join(tmpDir, 'mcp_settings.json');
+
+    originalSettingsEnv = process.env.MCPHUB_SETTING_PATH;
+    process.env.MCPHUB_SETTING_PATH = settingsPath;
+  });
+
+  afterEach(() => {
+    if (originalSettingsEnv === undefined) {
+      delete process.env.MCPHUB_SETTING_PATH;
+    } else {
+      process.env.MCPHUB_SETTING_PATH = originalSettingsEnv;
+    }
+
+    try {
+      fs.rmSync(tmpDir, { recursive: true, force: true });
+    } catch {
+      // ignore cleanup errors
+    }
+  });
+
+  it('does not rewrite settings when bearerKeys exists as an empty array', async () => {
+    writeSettings(settingsPath, {
+      mcpServers: {},
+      users: [],
+      systemConfig: {
+        routing: {
+          enableBearerAuth: false,
+          bearerAuthKey: '',
+        },
+      },
+      bearerKeys: [],
+    });
+
+    const writeSpy = jest.spyOn(fs, 'writeFileSync');
+
+    const dao = new BearerKeyDaoImpl();
+    const enabled1 = await dao.findEnabled();
+    const enabled2 = await dao.findEnabled();
+
+    expect(enabled1).toEqual([]);
+    expect(enabled2).toEqual([]);
+
+    // The DAO should NOT persist anything because bearerKeys already exists.
+    expect(writeSpy).not.toHaveBeenCalled();
+
+    writeSpy.mockRestore();
+  });
+
+  it('migrates legacy bearerAuthKey only once', async () => {
+    writeSettings(settingsPath, {
+      mcpServers: {},
+      users: [],
+      systemConfig: {
+        routing: {
+          enableBearerAuth: true,
+          bearerAuthKey: 'legacy-token',
+        },
+      },
+      // bearerKeys is intentionally missing to trigger migration
+    });
+
+    const writeSpy = jest.spyOn(fs, 'writeFileSync');
+
+    const dao = new BearerKeyDaoImpl();
+
+    const enabled1 = await dao.findEnabled();
+    expect(enabled1).toHaveLength(1);
+    expect(enabled1[0].token).toBe('legacy-token');
+    expect(enabled1[0].enabled).toBe(true);
+
+    const enabled2 = await dao.findEnabled();
+    expect(enabled2).toHaveLength(1);
+    expect(enabled2[0].token).toBe('legacy-token');
+
+    // One write for the migration, no further writes on subsequent reads.
+    expect(writeSpy).toHaveBeenCalledTimes(1);
+
+    writeSpy.mockRestore();
+  });
+});