Feature request: Request to add "InvokeMode: RESPONSE_STREAM" support for SAM "Api" events to enable Lambda response streaming through API Gateway.

[ajaypokale]

AWS Lambda and API Gateway support response streaming as documented in the AWS blog post
https://aws.amazon.com/blogs/compute/building-responsive-apis-with-amazon-api-gateway-response-streaming/

However, this feature is not available through SAM "Api" events

I wish sam cli should support InvokeMode: RESPONSE_STREAM
The cloud formation and cli is already supporting this property.

Code not working:

`
  ApiHandlerFun:
    Type: AWS::Serverless::Function
    Properties:
              CodeUri: apis-lambda/src
      Handler: ApiHandlerLambda.lambda_handler
      FunctionName: !Sub "${Stage}-ApiHandlerFun"
      Environment:
        Variables:
          AGENT_ID: !Ref AgentId
          AGENT_ALIAS_NAME: !Ref AgentAliasName
      Events:
        ChatStreamEventMessage:
          Type: Api
          Properties:
            RestApiId: !Ref ChatbotRestApi
            Path: /converse-stream
            Method: POST
            InvokeMode: RESPONSE_STREAM  # Enable streaming        
`

If I add above property (InvokeMode: RESPONSE_STREAM ) and run aws sam command then getting exception:
Number of errors found: 1. Resource with id [ChatStreamEventMessage] is invalid. property InvokeMode not defined for resource of type Api

SAM CLI Version: SAM CLI, version 1.144.0
Python Version:3.13

[bnusunny]

@ajaypokale Thanks for raising this feature request. In addition to what you asked, do you like to see this feature to be supported in sam local start-api?

[ajaypokale]

Hello,
Is there any tentative timeline or target release in which this feature will be available?
This currently blocking our development for streaming chat endpoints used by customers.

[DigitalVisionMax]

Hi Team,
We are also facing similar situation. This feature would help us in resolving our production issue.

Please prioritize this feature.

[seshubaws]

Hello, thank you for the request! We will prioritize getting support for response streaming in SAM API events in the next week or two. Adding support for it in sam cli (i.e in sam local start-api) might take a bit longer, we will discuss internally how to prioritize that.

[ajaypokale]

Checking in to see if there’s any update..

[ajaypokale]

Following up !!!

[ajaypokale]

Hi Team,
Waiting for an update on this case.

[reedham-aws]

Seems like the PR (aws/serverless-application-model#3881) is ready to merge, but the approval workflow started failing due to a dependency failure. After that's resolved, we should be able to merge it to SAM.

Edit: The fix has now been merged, but not released yet.

[ajaypokale]

Hello,
In which sam releases this feature will be available?
Thank you!