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To stream Amazon Bedrock output through AWS Lambda, call a Bedrock streaming operation, enable streaming in the Lambda handler, and write each incoming event to the Lambda response stream as it arrives. If API Gateway is the client-facing endpoint, use a REST API proxy integration configured for STREAM; its Lambda response also needs the required metadata-and-payload framing.
Choose a Bedrock streaming operation your model supports
For models that support the messages interface, ConverseStream provides a consistent way to receive generated content as a stream. For model-specific request formats, use InvokeModelWithResponseStream. These are streaming operations; a regular, non-streaming invocation returns a completed response instead.
Streaming support varies by model. AWS recommends calling GetFoundationModel and checking responseStreamingSupported before choosing an operation. Do not assume that every model supports ConverseStream or response streaming.
Use an AWS SDK or another supported client for the Bedrock request. The AWS CLI does not support Bedrock streaming operations.
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Stream the Bedrock events from Lambda
Lambda must use its response-streaming handler pattern; returning an ordinary buffered object is a different response path. In Node.js, AWS’s pattern wraps the handler with awslambda.streamifyResponse(), then writes output to the response stream as Bedrock events arrive. End the stream gracefully when generation finishes.
- Verify access. The function needs permission for the Bedrock streaming operation, such as
bedrock:InvokeModelWithResponseStreamfor the relevant request. Scope resources to the model or inference profile used by your deployment. - Wrap the handler. Use
awslambda.streamifyResponse()in the Node.js Lambda handler. - Start the Bedrock stream. Call the supported streaming operation with the model’s required request format.
- Forward events as they arrive. Write generated output to the Lambda response stream rather than waiting to assemble a complete response first.
- Finish cleanly. Close or end the response stream after the Bedrock generation completes, and handle errors so a failed generation does not leave the client waiting indefinitely.
The exact request fields and event contents depend on the chosen model interface, so use that model’s Bedrock API documentation when implementing event parsing.
Choose how clients reach the Lambda stream
A client can connect through a Lambda streaming endpoint, such as a function URL configured for response streaming, or through API Gateway. The right option depends on the client protocol and deployment requirements; the AWS documentation does not establish one as universally faster or better.
| Path | What to configure | Key distinction |
|---|---|---|
| Direct Lambda streaming endpoint | Enable response streaming for the endpoint and use a stream-enabled handler. | Avoids API Gateway’s REST API proxy response-framing requirement. |
| API Gateway REST API proxy | Use an AWS_PROXY or HTTP_PROXY integration and set the integration response transfer mode to STREAM. |
For a Lambda proxy integration, API Gateway invokes Lambda with InvokeWithResponseStream and expects the streaming response format. |
API Gateway must be permitted to invoke the Lambda function, and callers or other services also need the applicable lambda:InvokeFunction permissions. The required resource scope depends on your account, model, and integration. There is no single least-privilege policy that fits every deployment.
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AWS documents this mode for API Gateway REST APIs using proxy integrations. The default integration response transfer mode is BUFFERED; change it to STREAM to pass the Lambda response incrementally. This is response streaming, not request streaming: API Gateway does not support request streaming in this mode. AWS documents the mode for REST APIs, not HTTP APIs.
AWS describes reduced time to first byte for generative AI chatbots as a use case. That is a potential benefit of streaming, not a latency guarantee for a particular model, region, or application.
Use API Gateway’s response-stream helper
When constructing the response in Node.js, AWS’s configuration examples use awslambda.HttpResponseStream.from() to write the response metadata wrapper. The helper handles the wrapper and delimiter framing expected by API Gateway, so you do not need to construct the delimiter yourself.
Emit the framing manually only when needed
The API Gateway Lambda response stream begins with JSON metadata, then a delimiter, then the raw payload chunks. If you emit the framing yourself, AWS specifies that the delimiter is eight null bytes and must appear within the first 16 KB of the stream. A malformed or late delimiter can prevent the response from being interpreted as intended.
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Account for API Gateway’s duration and idle limits
AWS documents these limits for API Gateway response streaming:
| Constraint | AWS-documented limit |
|---|---|
| Maximum response-stream duration | Up to 15 minutes |
| Idle timeout, Regional or private endpoint | Five minutes |
| Idle timeout, edge-optimized endpoint | 30 seconds |
The endpoint type therefore matters if generation or pauses between output chunks could be long. These are service constraints, not a promise about how quickly a model will produce its first chunk or how frequently it will emit content.
Choose the implementation that matches your application
- Choose
ConverseStreamwhen the model supports Bedrock’s messages interface and you want its consistent message-oriented API. - Choose
InvokeModelWithResponseStreamwhen you need the model-specific invocation interface. - Use a direct Lambda streaming endpoint when it meets your client and deployment needs without API Gateway’s proxy framing.
- Use an API Gateway REST API proxy when you need that HTTP front door and can configure
STREAMmode and its response format. - Prefer helper-managed framing unless your implementation has a reason to emit the response metadata and delimiter manually.
The Bedrock-to-Lambda response stream described here is application-level inference streaming. It is separate from Amazon Bedrock Agents’ Lambda action-group integration, which has a different contract.
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