LangGraph: State Machines for Reliable Agents

The first version of every agent looks like this, in one breath:

code
Copy
  while not done:
      answer = model(messages)
      if answer wants a tool: run it, append result
      else: done

It works on your laptop. Then production files a complaint, four counts:

• The process crashed at tool 4 of 5. Where were you? Inside the loop. All four earlier steps — and their side effects — are gone or, worse, half-happened.
• The refund agent refunded twice after a retry restarted the loop from the top. Nobody approved anything.
• Legal asks: "show me exactly what the agent knew before it wrote that." You have a log soup.
• Product asks: "let the user edit step 2 and re-run from there." You have no step 2 to edit.

A while-loop is a story about control flow, remembered only in RAM and print statements. Serious workflows — the kind banks, hiring tools, and ops teams run — need control flow you can see, pause, save, and replay.

So the question becomes

That is LangGraph (LangChain Inc., 2024; 1.0 in October 2025) — the runtime that LangChain's own agents now sit on (Topic 279).