Durable Functions in Lambda, unveiled at Reinvent 2025, let developers build multi‑step workflows that pause and resume, running up to a year. Each run is a durable execution that preserves state through checkpoints, enabling automatic recovery without custom retry logic.

The checkpoint‑and‑replay mechanism records progress before and after each durable step. When a function resumes, it re‑runs from the start but skips completed work, reusing stored results. This guarantees consistency and eliminates the need for manual idempotency handling.

Typical scenarios include order processing—reserve inventory, process payment, confirm shipment—where retries must not duplicate actions. Durable Functions also support external ERP callbacks, human approvals, and exponential backoff for API calls, all without polling or extra infrastructure.

Developers create them via the Lambda console or IaC, using NodeJS or Python decorators. Currently available only in Ohio, the feature shows executions in a new tab and logs in CloudWatch. Choose Durable Functions for code‑first, long‑running logic; Step Functions for multi‑service orchestration.