[catlifeonmars]

Each container handles requests serially. This doesn’t preclude you from spawning multiple threads in Lambda to do background work though.

[shortstuffsushi]

Serially, but up to ten requests in a single batch

> By default, Lambda polls up to 10 messages in your queue at once and sends that batch to your function.

From https://docs.aws.amazon.com/lambda/latest/dg/with-sqs.html