Which AWS service tracks API calls and user activity?

Explanations:

AWS Organizations is used for managing multiple AWS accounts and policies across those accounts. It does not track API calls or user activity.

AWS Config is a service that provides a detailed view of the configuration of AWS resources in your account. It monitors resource configuration changes but not API calls.

Amazon CloudWatch is primarily for monitoring and observability of AWS resources and applications, including performance metrics and logs, but does not specifically track API calls.

AWS CloudTrail is specifically designed to log and monitor API calls made in an AWS account. It captures user activity, providing detailed event logs for auditing and compliance.