LLM: Describe the job; let a model do it at runtime
A prompt and a few tools get a working version the same day. Iterate by editing text.
✦Better models, agent SDKs and tool calling make the first prototype close to production quality.
Unstructured text, PDFs, images, languages, typos. It covers cases no one would ever write a rule for.
✦Each model generation takes on messier inputs with less prompting.
Swap in a newer model and quality goes up without touching your code.
✦Model upgrades arrive every few months. That's R&D you get without paying for it.
New policy? Edit the prompt, re-run evals, ship. Domain experts can do it too.
✦This was always true. What's changed is that evals make it safe.
Users and operators just ask. No forms and no training on a new UI.
✦Users now expect to be able to just ask.
The same input can produce different outputs. You need evals, guardrails and human review for high-stakes paths.
✦Structured outputs, better models and eval tooling reduce variance, but it never reaches zero.
Every request pays tokens and seconds. At millions of calls, the unit economics can dominate.
✦The price for a given capability has been falling several-fold per year, and small models cover more tasks.
Confident wrong answers. Dangerous where money, health or law is involved.
✦Grounding, tool use and verification loops help. High-stakes paths still need deterministic checks.
Untrusted input can steer the model. Tools with side effects need strict permissioning.
✦Still an open problem. Treat model output as untrusted input.
It's hard to explain to an auditor why the model decided X. There's no line of code to point at.
✦Traces help, but regulators still want deterministic, explainable decision paths.
- →Inputs are unstructured or open-ended
- →An occasional error is cheap and can be caught
- →The spec is unclear. Use the LLM to discover it
- →Volume is moderate, or cost per call is falling fast
- why it mattersTreat the prompt as code. Version it, test it with evals, and review changes to it. Otherwise nobody can say what the system does.
- why it mattersLLM output is untrusted input. Validate it with schemas, and put deterministic checks in front of anything that moves money.
- why it mattersOnce an LLM flow stabilises and volume grows, have an agent turn the learned behaviour into deterministic code. Keep the model for the long tail.