Cookbook

Recipes for working with Fable

Each recipe is one task pattern: when to use it, working code, and the pitfalls — verified against the Claude API reference, not model memory.

Guide current as of June 11, 2026. Fable 5 is included on Pro/Max/Team plans through June 22; usage credits apply after. Latest news →

Each recipe page below contains runnable, copy-paste code examples verified against the Claude API.

Recipe 01 Migrate from Opus The one-line model swap, and the five old habits that now return 400.
Recipe 02 Agentic loops & tools The tool runner, the manual loop, and tool descriptions Fable actually triggers on.
Recipe 03 Structured outputs Guaranteed-valid JSON with Pydantic or raw schemas — the replacement for prefills.
Recipe 04 Prompt caching At $10/MTok input, caching is the difference between affordable and not.
Recipe 05 Memory files Fable is unusually good at keeping notes. Give it somewhere to keep them.
Recipe 06 Task budgets Give long agentic runs a token allowance the model can see and pace itself against.

The capstone Put the recipes together: build an autonomous agent → These six recipes are the moving parts. The nine-layer field guide assembles them into a system you can leave running — a constitution, separation of powers, earned-trust ledgers, budgets, and injection defense.

Every recipe has a machine-readable twin in /api/cookbook.json. Found an error? The primary sources are the announcement and platform.claude.com/docs — trust those over us.