The short version: a Lambda function can now checkpoint its state, sleep for hours or days, and resume exactly where it left off — without paying for idle time. I rebuilt a human-in-the-loop expense approval workflow to test it. Before: Lambda + DynamoDB + Step Functions + SQS + EventBridge. After: two Lambda functions and an API Gateway. The function literally looks like this: ``ts const decision = await context.waitForCallback( 'wait-for-approval', async (callbackId) => sendApprovalEmail(expense, callbackId), { timeout: { hours: 24 } } ); `` It pauses there. Zero compute. Waits up to 24h for someone to click approve. Then resumes on the next line. Wrote up the full architecture, CDK stack, and where Step Functions still wins: https://medium.com/itnext/is-step-functions-still-necessary-the-case-for-lambda-durable-functions-in-2026-22f5a5f4a1a3 Happy to answer questions about the implementation. submitted by /u/hoangdv-i368 [link] [comments]