Effective August 1, 2025, AWS will standardize billing for the initialization (INIT) phase across all AWS Lambda function configurations. This change specifically affects on-demand invocations of Lambda functions packaged as ZIP files that use managed runtimes, for which the INIT phase duration was previously unbilled. This update standardizes billing of the INIT phase across all runtime types, deployment packages, and invocation modes. In this post, we discuss the Lambda Function Lifecycle and upcoming changes to INIT phase billing. You will learn what happens in the INIT phase and when it occurs, how to monitor your INIT phase duration, and strategies to optimize this phase and minimize costs.
Effective August 1, 2025, AWS will start billing for compute used during INIT phases. No more doing lots of work in your init phase for free
Since AWS controls when the function is expired from warm start to cold start, it’s a guarantee they’re going to become extra aggressive about terminating idle functions.
Why leave customer code loaded for free when you can charge for startup again?
That’s an inherent problem with serverless/functions as a service. There’s no guarantee at all on it staying warm for a given amount of time and any system that depended on it without paying for provisioned concurrency was just depending on hopes and dreams.
Since AWS controls when the function is expired from warm start to cold start, it’s a guarantee they’re going to become extra aggressive about terminating idle functions.
Why leave customer code loaded for free when you can charge for startup again?
That’s an inherent problem with serverless/functions as a service. There’s no guarantee at all on it staying warm for a given amount of time and any system that depended on it without paying for provisioned concurrency was just depending on hopes and dreams.