AWS shows how to cut idle costs when AI agents process requests

Key takeaway

• AWS published guidance on three asynchronous invocation patterns for calling Amazon Bedrock AgentCore agents in serverless pipelines that eliminate idle compute costs.

• When an AI agent is reasoning through a document or task, a synchronous caller—such as a Lambda function—normally blocks and incurs billing for its entire processing time, even though it is doing nothing.

• The three patterns release the caller's compute during the wait and resume only when the agent returns a result, shifting the cost from the idle caller to the agent's consumption-based model.

3 Key Points

Context & Analysis

FAQ

Why does a blocking Lambda function cost more than an asynchronous one?

A Lambda function that issues a synchronous call to an agent sits blocked on an open connection, holding and paying for its full compute allocation until the agent responds. In contrast, a function that starts the agent and returns is billed only for the brief dispatch—a few seconds—because the function has already shut down while the agent works in the background.

Which pattern removes the Lambda function entirely?

Pattern 2 (direct service integration) eliminates the dispatcher Lambda by having Step Functions call Amazon Bedrock AgentCore directly through its AWS SDK service integration, so the agent's response flows straight into the next state.

How does an agent resume a paused execution after it finishes thinking?

In Pattern 1, the agent calls a Lambda that posts the result and the task token back to Step Functions using SendTaskSuccess. In Pattern 3, the agent resumes the durable function using SendDurableExecutionCallbackSuccess with a callback ID.