Amazon Bedrock AgentCore ships a new default runtime with sub-2-second cold starts

AWS introduced a new default runtime for Amazon Bedrock AgentCore that cuts agent cold-start latency from about 30 seconds to under 2 seconds and scales idle agents to zero, starting November 12, 2026.

Amazon Web Services (AWS) announced on November 12, 2026, that Amazon Bedrock AgentCore now ships with a new default runtime designed to cut agent cold-start latency, according to AWS's announcement of the new AgentCore runtime.

The concrete changes

Agent sessions now initialize from snapshots and scale compute and memory dynamically, with idle agents scaling to zero.
Startup latency drops to under 2 seconds at the P75 mark, down from roughly 30 seconds with the previous runtime.
Sessions can use up to 8 vCPU and 32GB of memory, with containers sized up to 10GB.
AWS says the new runtime uses up to 68% less billed memory for multi-turn agent sessions.
The runtime runs inside Firecracker microVMs.
The new default is live across 19 AWS regions, while existing AgentCore runtimes keep their prior behavior until a customer opts in by setting platformVersion: V2.

What it means for people building AI agents

Cold-start latency and the cost of keeping agents warm are two of the most common practical complaints from teams running production AI agents on AWS. This update targets both directly: because idle agents scale to zero and sessions restart from a snapshot in under 2 seconds, builders can stop paying to keep agents resident just to avoid slow restarts, and the lower billed memory for multi-turn sessions should narrow the gap between running agents continuously and running them on demand.

Availability and next steps

Because the change only affects the default runtime, teams already running Amazon Bedrock AgentCore keep their current setup unless they choose to migrate, giving them control over when to adopt the new behavior rather than having it forced on existing workloads.

Sources

New default runtime for Amazon Bedrock AgentCore (Amazon Web Services, November 12, 2026, official)

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