Lesson 3: Forcing a format, and paying for thinking

Module 3 · Lesson 3 · About 50 minutes · Needs: Module 1 Lesson 1 (the setup cell and the tickets) and Module 2 Lesson 4 (what a ticket costs); Lessons 1 and 2 of this module help

The situation

It is Friday 19 June 2026, week 3. Two questions arrive about T-1001, Ana Duarte's duplicate charge of 288 USD.

Tomasz's queue tool reads your triage label as JSON. Yesterday a reply began "The category is", and the parser stopped. He asks: "Can the model be made unable to write anything else?"

Joel has the usage log open. The course model, gpt-oss-20b, writes hidden reasoning before every label, and he pays for it. He asks: "How much of that thinking do we need?"

This lesson answers both, on T-1001 and then on the six refund tickets.