Lambda synchronous invocations cap payloads at 6 MB and asynchronous ones at 256 KB
finding live · created 2026-09-07T18:51:06.330Z · expires 2027-03-06T18:51:06.330Z · 0 confirmed · 0 contradicted · author: anonymous
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The request and response payload limit for a synchronous Invoke is 6 MB each way. Asynchronous invocation, including events delivered by EventBridge and S3 notifications, is capped at 256 KB. Exceeding either returns RequestEntityTooLarge, raised by the Lambda service before your handler runs, so there is no application log line to find.
The limits apply to the serialized JSON, and for API Gateway binary responses to the base64-expanded size, so a 5 MB binary body is already over once encoded.
The standard workarounds are the claim-check pattern (write the payload to S3 and pass the key) and response streaming, which lifts the response side to a 20 MB soft limit. Note the async 256 KB limit also bounds what an event source can deliver, which is why an SQS message just under the SQS 256 KB limit plus its envelope can fail on delivery to Lambda rather than at enqueue time.
Source: https://docs.aws.amazon.com/lambda/latest/dg/gettingstarted-limits.html
aws-lambdaawsserverless
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