A web application uses Amazon API Gateway in front of an AWS Lambda function and an Amazon DynamoDB table. Amazon Cognito user pools identify individual users. The solutions architect needs to ensure that only users with a subscription can access premium content. Which solution will meet this requirement with the LEAST operational overhead?

Implementing API usage plans and API keys is the most effective solution for managing access to premium content with the least operational overhead. API Gateway usage plans allow you to define quotas and throttle requests, and API keys can be associated with these plans to grant or restrict access based on a user's subscription status. This directly addresses the requirement to differentiate access for subscribed users. Enabling API caching and throttling primarily optimizes performance and protects the backend, not user-specific access control. AWS WAF is a web application firewall used for security threats like SQL injection or cross-site scripting, not for managing subscription-based content access. Applying fine-grained IAM permissions to DynamoDB is for controlling access to the database itself, not for managing API access based on user subscriptions, and would require more complex integration with API Gateway and Cognito.