tl;dr: AWS Lambda MicroVMs is a new serverless primitive that provides Firecracker-based, VM-level isolated sandboxes for running untrusted user- or AI-generated code, with near-instant launch via pre-initialized snapshots and stateful execution that persists memory/disk across suspend/resume cycles. It targets use cases like AI coding assistants, interactive code environments, and game servers running user scripts—filling the gap between slow-booting VMs, shared-kernel containers, and stateless FaaS. Available now in four regions on ARM64, supporting up to 16 vCPUs, 32 GB RAM, 32 GB disk, and 8-hour runtimes.