diff --git a/packages/web/.env.example b/packages/web/.env.example
index 1145c15..a877d0d 100644
--- a/packages/web/.env.example
+++ b/packages/web/.env.example
@@ -23,3 +23,8 @@ AWS_REGION=us-east-1
 # Set to 'false' or leave unset for standard auth (local development)
 # NOTE: IAM auth automatically enables TLS/SSL encryption (required by AWS)
 USE_IAM_AUTH=false
+
+# Redis/ElastiCache username for IAM authentication
+# Must match an IAM-enabled user created in ElastiCache User Group
+# Only used when USE_IAM_AUTH=true
+REDIS_USERNAME=tonys-chips-web
diff --git a/packages/web/src/index.ts b/packages/web/src/index.ts
index 36d6161..f999b5c 100644
--- a/packages/web/src/index.ts
+++ b/packages/web/src/index.ts
@@ -34,14 +34,29 @@ async function initializeRedisClient(): Promise<RedisClientType> {
     const url = new URL(redisUrl);
     const host = url.hostname;
     const port = parseInt(url.port) || 6379;
-    const username = 'tonys-chips-web'; // Must match ElastiCache User
+    // Username must match an IAM-enabled ElastiCache user
+    // For Serverless: often 'default' or a custom IAM user created in ElastiCache
+    // For regular clusters: custom username from ElastiCache User configuration
+    const username = process.env.REDIS_USERNAME || 'tonys-chips-web';
+
+    // Detect if this is a serverless cache
+    const isServerless = host.includes('.serverless.');
 
     console.log('Initializing Valkey client with IAM authentication...');
     console.log(`Connecting to: ${host}:${port}`);
+    console.log(`Cache Type: ${isServerless ? 'Serverless' : 'Regular Cluster'}`);
+    console.log(`Username: ${username}`);
+    console.log(`AWS Region: ${awsRegion}`);
     console.log('TLS encryption: ENABLED (required for IAM auth)');
 
     // Generate initial IAM auth token
-    const token = await generateIAMAuthToken(host, port, username, awsRegion);
+    console.log('Generating IAM authentication token...');
+    const token = await generateIAMAuthToken(host, port, username, awsRegion, isServerless);
+    console.log(`Generated token length: ${token.length} characters`);
+    console.log(`Token preview: ${token.substring(0, 100)}...`);
+    if (isServerless) {
+      console.log('Token includes ResourceType=ServerlessCache parameter');
+    }
 
     // Create Redis client with IAM credentials and TLS
     // TLS is REQUIRED for IAM authentication with AWS ElastiCache
diff --git a/packages/web/src/utils/elasticache-iam-auth.ts b/packages/web/src/utils/elasticache-iam-auth.ts
index da86712..07673d5 100644
--- a/packages/web/src/utils/elasticache-iam-auth.ts
+++ b/packages/web/src/utils/elasticache-iam-auth.ts
@@ -8,8 +8,9 @@ import { Sha256 } from '@aws-crypto/sha256-js';
  *
  * Based on AWS SigV4 signing process:
  * 1. Creates a pre-signed URL with Action=connect&User=username
- * 2. Signs the URL with AWS credentials
- * 3. Returns the signed token (without http:// prefix) for use as password
+ * 2. For Serverless: includes ResourceType=ServerlessCache
+ * 3. Signs the URL with AWS credentials
+ * 4. Returns the signed token (without http:// prefix) for use as password
  *
  * Tokens are valid for 15 minutes.
  *
@@ -17,18 +18,36 @@ import { Sha256 } from '@aws-crypto/sha256-js';
  * @param port - ElastiCache cluster port (typically 6379)
  * @param username - IAM-enabled ElastiCache username
  * @param region - AWS region
+ * @param isServerless - Whether this is a Serverless cache (default: auto-detect from endpoint)
  * @returns Signed authentication token to use as password
  */
 export async function generateIAMAuthToken(
   endpoint: string,
   port: number,
   username: string,
-  region: string
+  region: string,
+  isServerless?: boolean
 ): Promise<string> {
   // Get AWS credentials from the environment (ECS task role in production)
   const credentialProvider = fromNodeProviderChain();
   const credentials = await credentialProvider();
 
+  // Auto-detect if this is a serverless cache based on endpoint
+  const detectServerless = isServerless !== undefined
+    ? isServerless
+    : endpoint.includes('.serverless.');
+
+  // Create query parameters
+  const query: Record<string, string> = {
+    Action: 'connect',
+    User: username,
+  };
+
+  // Add ResourceType for Serverless caches (REQUIRED)
+  if (detectServerless) {
+    query.ResourceType = 'ServerlessCache';
+  }
+
   // Create the HTTP request to sign
   const request = new HttpRequest({
     method: 'GET',
@@ -36,10 +55,7 @@ export async function generateIAMAuthToken(
     hostname: endpoint,
     port,
     path: '/',
-    query: {
-      Action: 'connect',
-      User: username,
-    },
+    query,
     headers: {
       host: `${endpoint}:${port}`,
     },