1
What Is Claude Fable 5? The Mythos-Class Tier Explained
Understand Fable 5's position as the first Claude 5 model, the new Mythos-class tier above Opus, and how Claude Mythos 5 and Project Glasswing fit in.
Start lessonIntroduction to Claude Fable 5
What the Mythos-class tier is, how Fable 5 differs from every Claude before it, and how to make your first API call against the new request shape.
Lessons in this module
Follow the lessons sequentially for best understanding
2
Environment Setup & Your First Fable 5 API Call
Configure your environment, install the SDK, and make a working Fable 5 request with output_config — plus the streaming setup you will need for real workloads.
Start lesson3
The New API Contract: What Changed, What 400s
A complete inventory of Fable 5's API surface changes — removed sampling parameters, mandatory thinking, no prefill, retention requirements — and how to audit existing code for them.
Start lessonKey skills
What you'll master in this module
Practical knowledge
Gain practical experience you can apply immediately
Expertise
Develop deeper domain expertise
Communication
Learn to communicate your knowledge effectively
Documentation
Create your own notes and documentation
Problem analysis
Learn systematic approaches to complex problems
Optimization
Optimize for performance and efficiency
Tips for success
How to get the most out of this module
1
Proceed step by step
Don't move on until you fully understand the previous lesson
2
Practice regularly
Spend daily time on the practical lesson exercises
3
Take notes
Write down key insights and your own thoughts
4
Ask questions
If something is unclear, ask the community for help
5
Test knowledge
Validate learning with exercises and quizzes
6
Share insights
Teach concepts to others to reinforce retention