The default concurrency limit per AWS Region is 1,000 invocations at any given time.

The default burst concurrency quota per Region is between 500 and 3,000, which varies per Region.

There is no maximum concurrency limit for Lambda functions. However, limit increases are granted only if the increase is required for your use case.

To avoid throttling, it's a best practice to request a limit increase at least two weeks prior to when the increase is needed.

If you're using Lambda with CloudFront Lambda@Edge, then you must open a separate quota increase case for each Region.

Each instance of your execution environment can serve up to 10 requests per second. In other words, the total invocation limit is 10 times your concurrency

https://cloudash.dev/blog/best-practices-for-optimizing-lambda-functions