Wiring a System One model into a feature

A System One model answers typed questions in one forward pass. It generates no text. State in, typed answers with calibrated probabilities out. It is an if-statement that can read.

Use it when the decision is narrow, pre-specified, and repeated. Do not use it for anything that needs a written explanation — that is still a job for Claude.

Before anything else: is this actually the right tool

Answer these three. If any is "no", stop and keep the LLM call.

1. Are the possible answers known up front? Choice caps at 255 options.
2. Does the caller need only the label, not the reasoning? If a human reads a justification downstream, you need prose and this is the wrong tool.
3. Is it high volume, or is a person waiting? This is a latency and cost optimisation, not a capability gain. It knows nothing Claude doesn't. On a nightly cron over fifty records it buys you a dependency and nothing else.