Guardrails in under 40 milliseconds
Policy checks that add no noticeable latency: small models, early exits and a lot of caching.

Published
Category
Engineering
Author
Mei Tan
Reading
6 min
Policy checks that add no noticeable latency: small models, early exits and a lot of caching. At Signa we spend most of our time reading traces, and most of what we know comes from failures our customers were brave enough to share.
Where it starts
Most teams begin with a spreadsheet of fifty questions and a thumbs-up column. It is a fine start and a poor finish: it measures the model, not the agent, and it never sees the long tail.
What we do instead
We score the whole run — retrieval, tool choice, arguments, final answer and policy — and we weight each case by how often it happens and how much it costs when it goes wrong.
Every automated judge is calibrated against human graders before its scores count toward a release gate.
What to take away
Measure the thing your customers experience, calibrate the thing that measures it, and keep the evidence. The rest is tooling.