This should be a 1000 concurrent executions, and it's a soft limit. So you can raise this to 10s of thousands if you need, but the SQS-polling Lambda that Lambda has would only use up to 1000 https://docs.aws.amazon.com/lambda/latest/dg/with-sqs.html#events-sqs-scaling so if you want to go beyond 1000 concurrent executions you'd have to ditch SQS.

Also, given the way SQS scales the no. of pollers (starts with 5 then goes up by 60 per minute based on the size of the backlog) if you want to process things as quickly as possible, then SQS would take a few minutes to reach max concurrency.