AWS Lambda Pricing & Plans

A cold start occurs when AWS Lambda must initialize a brand-new execution environment because no pre-warmed instance is available — this happens on the first invocation, after a period of inactivity, or during rapid traffic scaling. During this INIT phase, AWS allocates infrastructure, downloads your deployment package, boots the runtime, and runs your initialization code, which adds latency to that request. As of August 1, 2025, this INIT phase duration is now billed for all Lambda configurations. You can mitigate cold starts using Provisioned Concurrency (which pre-warms a set number of execution environments) or Lambda SnapStart (available for Java runtimes).