AWS Lambda occasionally pre-initializes execution environments to reduce the number of cold start invocations. This is known as proactive initialization, and it can occur even when features like Provisioned Concurrency are not being used. Proactive initialization serves the interests of both AWS and developers running applications on Lambda, as it minimizes CPU time in a shared, multi-tenant system. It occurs more frequently than true cold starts, with a percentage that varies depending on factors such as workload and latency tolerance. Developers can observe proactive initializations using tools like CloudWatch Logs Insights or Datadog. By tracking this behavior, developers can focus on their own applications while AWS improves the underlying infrastructure.