diff --git a/packages/apps/src/middleware/auth/jwt-validator.ts b/packages/apps/src/middleware/auth/jwt-validator.ts
index 9db9a8dfb..eb1791321 100644
--- a/packages/apps/src/middleware/auth/jwt-validator.ts
+++ b/packages/apps/src/middleware/auth/jwt-validator.ts
@@ -9,6 +9,15 @@ const DEFAULTS = {
   clockTolerance: 300 // 5 minutes
 };
 
+export function decodeJwtPayload(rawToken: string): JwtPayload | null {
+  const payload = jwt.decode(rawToken);
+  if (!payload || typeof payload !== 'object') {
+    return null;
+  }
+
+  return payload;
+}
+
 export interface IJwtValidationOptions {
   /** Required: Application/Client ID for audience validation */
   clientId: string;
@@ -296,4 +305,3 @@ export const createEntraTokenValidator = (
     },
   }, options?.logger);
 };
-
diff --git a/packages/apps/src/middleware/auth/service-token-validator.spec.ts b/packages/apps/src/middleware/auth/service-token-validator.spec.ts
index 775282b16..5ea58aa5e 100644
--- a/packages/apps/src/middleware/auth/service-token-validator.spec.ts
+++ b/packages/apps/src/middleware/auth/service-token-validator.spec.ts
@@ -3,8 +3,14 @@ import { US_GOV, CHINA } from '@microsoft/teams.api';
 import { JwtValidator } from './jwt-validator';
 import { ServiceTokenValidator } from './service-token-validator';
 
-// Mock JwtValidator
-jest.mock('./jwt-validator');
+// Mock JwtValidator — real one fetches JWKS keys from remote endpoints.
+jest.mock('./jwt-validator', () => {
+  const actual = jest.requireActual('./jwt-validator');
+  return {
+    ...actual,
+    JwtValidator: jest.fn(),
+  };
+});
 
 describe('ServiceTokenValidator', () => {
   const mockClientId = 'test-client-id';
@@ -13,6 +19,14 @@ describe('ServiceTokenValidator', () => {
 
   let mockValidateAccessToken: jest.Mock;
 
+  const createUnverifiedToken = (payload: Record<string, any>) => {
+    return [
+      Buffer.from(JSON.stringify({ alg: 'RS256', typ: 'JWT' })).toString('base64url'),
+      Buffer.from(JSON.stringify(payload)).toString('base64url'),
+      'signature'
+    ].join('.');
+  };
+
   beforeEach(() => {
     mockValidateAccessToken = jest.fn();
     (JwtValidator as jest.Mock).mockImplementation(() => ({
@@ -169,6 +183,103 @@ describe('ServiceTokenValidator', () => {
 
       expect(result.serviceUrl).toBe(bodyServiceUrl);
     });
+
+    it('should use service validator for Bot Framework tokens', async () => {
+      const validator = new ServiceTokenValidator(mockClientId, mockTenantId);
+      mockValidateAccessToken.mockResolvedValue({
+        appid: mockClientId,
+        sub: 'bot-id',
+        serviceurl: mockServiceUrl,
+      });
+
+      const token = createUnverifiedToken({ iss: 'https://api.botframework.com' });
+      await validator.check(`Bearer ${token}`, { serviceUrl: mockServiceUrl });
+
+      expect(mockValidateAccessToken).toHaveBeenCalledWith(token, {
+        validateServiceUrl: { expectedServiceUrl: mockServiceUrl }
+      });
+    });
+
+    it('should use Entra validator for v2 issuer tokens without serviceUrl validation', async () => {
+      const validator = new ServiceTokenValidator(mockClientId, mockTenantId);
+      mockValidateAccessToken.mockResolvedValue({
+        appid: mockClientId,
+        sub: 'agent-id',
+      });
+
+      const token = createUnverifiedToken({
+        iss: `https://login.microsoftonline.com/${mockTenantId}/v2.0`,
+        tid: mockTenantId,
+      });
+      await validator.check(`Bearer ${token}`, { serviceUrl: mockServiceUrl });
+
+      expect(JwtValidator).toHaveBeenLastCalledWith(expect.objectContaining({
+        clientId: mockClientId,
+        tenantId: mockTenantId,
+        loginEndpoint: 'https://login.microsoftonline.com',
+        validateIssuer: { allowedTenantIds: [mockTenantId] },
+        jwksUriOptions: { type: 'tenantId' },
+      }), undefined);
+      expect(mockValidateAccessToken).toHaveBeenLastCalledWith(token);
+    });
+
+    it('should use Entra validator for v1 sts issuer tokens', async () => {
+      const validator = new ServiceTokenValidator(mockClientId, mockTenantId);
+      mockValidateAccessToken.mockResolvedValue({ appid: mockClientId, sub: 'agent-id' });
+
+      const token = createUnverifiedToken({
+        iss: `https://sts.windows.net/${mockTenantId}/`,
+        tid: mockTenantId,
+      });
+      await validator.check(`Bearer ${token}`, { serviceUrl: mockServiceUrl });
+
+      expect(mockValidateAccessToken).toHaveBeenLastCalledWith(token);
+    });
+
+    it('should reject Entra tokens missing tid', async () => {
+      const validator = new ServiceTokenValidator(mockClientId, mockTenantId);
+      const token = createUnverifiedToken({
+        iss: `https://login.microsoftonline.com/${mockTenantId}/v2.0`,
+      });
+
+      await expect(validator.check(`Bearer ${token}`, { serviceUrl: mockServiceUrl }))
+        .rejects.toThrow('Entra inbound token is missing tid');
+    });
+
+    it('should cache Entra validators by tenant', async () => {
+      const validator = new ServiceTokenValidator(mockClientId, mockTenantId);
+      mockValidateAccessToken.mockResolvedValue({ appid: mockClientId, sub: 'agent-id' });
+      const token = createUnverifiedToken({
+        iss: `https://login.microsoftonline.com/${mockTenantId}/v2.0`,
+        tid: mockTenantId,
+      });
+
+      await validator.check(`Bearer ${token}`, { serviceUrl: mockServiceUrl });
+      await validator.check(`Bearer ${token}`, { serviceUrl: mockServiceUrl });
+
+      // Only one Entra validator created despite two calls (plus the BotFramework one in constructor)
+      const cache = (validator as any).entraValidatorsByTenantId as Map<string, any>;
+      expect(cache.size).toBe(1);
+    });
+
+    it('should bound Entra validator cache size', async () => {
+      const validator = new ServiceTokenValidator(mockClientId, mockTenantId);
+      mockValidateAccessToken.mockResolvedValue({ appid: mockClientId, sub: 'agent-id' });
+
+      for (let i = 0; i < 101; i++) {
+        const tenantId = `tenant-${i}`;
+        const token = createUnverifiedToken({
+          iss: `https://login.microsoftonline.com/${tenantId}/v2.0`,
+          tid: tenantId,
+        });
+        await validator.check(`Bearer ${token}`, { serviceUrl: mockServiceUrl });
+      }
+
+      const cache = (validator as any).entraValidatorsByTenantId as Map<string, JwtValidator>;
+      expect(cache.size).toBe(100);
+      expect(cache.has('tenant-0')).toBe(false);
+      expect(cache.has('tenant-100')).toBe(true);
+    });
   });
 
   describe('sovereign cloud support', () => {
diff --git a/packages/apps/src/middleware/auth/service-token-validator.ts b/packages/apps/src/middleware/auth/service-token-validator.ts
index 6eb7ef46f..e5d7505e9 100644
--- a/packages/apps/src/middleware/auth/service-token-validator.ts
+++ b/packages/apps/src/middleware/auth/service-token-validator.ts
@@ -1,7 +1,12 @@
+import { JwtPayload } from 'jsonwebtoken';
+
 import { CloudEnvironment, Credentials, IToken, PUBLIC } from '@microsoft/teams.api';
 import { ILogger } from '@microsoft/teams.common';
 
-import { JwtValidator } from './jwt-validator';
+import { JwtValidator, decodeJwtPayload } from './jwt-validator';
+
+const MAX_ENTRA_VALIDATOR_CACHE_SIZE = 100;
+const ENTRA_V1_ISSUER_PREFIX = 'https://sts.windows.net/';
 
 /**
  * Derives the JWKS keys URI from an OpenID metadata URL.
@@ -18,7 +23,11 @@ function openIdMetadataToKeysUri(openIdMetadataUrl: string): string {
  */
 export class ServiceTokenValidator {
   private jwtValidator: JwtValidator;
+  private entraValidatorsByTenantId = new Map<string, JwtValidator>();
   private credentials?: Credentials;
+  private appId: string;
+  private cloud: CloudEnvironment;
+  private logger?: ILogger;
 
   constructor(
     appId: string,
@@ -28,6 +37,9 @@ export class ServiceTokenValidator {
     cloud?: CloudEnvironment
   ) {
     const env = cloud ?? PUBLIC;
+    this.appId = appId;
+    this.cloud = env;
+    this.logger = logger;
     this.jwtValidator = new JwtValidator({
       clientId: appId,
       tenantId,
@@ -49,10 +61,13 @@ export class ServiceTokenValidator {
       ? authHeader.substring(7)
       : authHeader;
 
-    // Validate token using JWT validator
-    const payload = await this.jwtValidator.validateAccessToken(token, {
-      validateServiceUrl: body.serviceUrl ? { expectedServiceUrl: body.serviceUrl } : undefined
-    });
+    const unverifiedPayload = this.decodePayload(token);
+    const isEntraToken = this.isEntraIssuer(unverifiedPayload?.iss);
+    const payload = isEntraToken
+      ? await this.validateEntraToken(token, unverifiedPayload)
+      : await this.jwtValidator.validateAccessToken(token, {
+        validateServiceUrl: body.serviceUrl ? { expectedServiceUrl: body.serviceUrl } : undefined
+      });
 
     if (!payload) {
       throw new Error('Invalid token');
@@ -69,4 +84,49 @@ export class ServiceTokenValidator {
       isExpired: () => false, // Already validated by JWT validator
     };
   }
+
+  private decodePayload(rawToken: string): JwtPayload | null {
+    return decodeJwtPayload(rawToken);
+  }
+
+  private isEntraIssuer(issuer: unknown): issuer is string {
+    return typeof issuer === 'string' && (
+      issuer.startsWith(this.cloud.loginEndpoint) || issuer.startsWith(ENTRA_V1_ISSUER_PREFIX)
+    );
+  }
+
+  private async validateEntraToken(rawToken: string, unverifiedPayload: JwtPayload | null) {
+    const tenantId = unverifiedPayload?.tid;
+    if (!tenantId || typeof tenantId !== 'string') {
+      throw new Error('Entra inbound token is missing tid');
+    }
+
+    const validator = this.getEntraValidator(tenantId);
+    // Agent 365 inbound Entra tokens currently do not include serviceurl.
+    // Revisit service URL validation when the platform defines a signed claim.
+    return await validator.validateAccessToken(rawToken);
+  }
+
+  private getEntraValidator(tenantId: string) {
+    const cachedValidator = this.entraValidatorsByTenantId.get(tenantId);
+    if (cachedValidator) {
+      return cachedValidator;
+    }
+
+    const validator = new JwtValidator({
+      clientId: this.appId,
+      tenantId,
+      loginEndpoint: this.cloud.loginEndpoint,
+      validateIssuer: { allowedTenantIds: [tenantId] },
+      jwksUriOptions: { type: 'tenantId' },
+    }, this.logger);
+    this.entraValidatorsByTenantId.set(tenantId, validator);
+    if (this.entraValidatorsByTenantId.size > MAX_ENTRA_VALIDATOR_CACHE_SIZE) {
+      const oldestTenantId = this.entraValidatorsByTenantId.keys().next().value;
+      if (oldestTenantId) {
+        this.entraValidatorsByTenantId.delete(oldestTenantId);
+      }
+    }
+    return validator;
+  }
 }