Claude Fable 5
The detail obsessive — Anthropic's most capable widely released model.
Mythos 5 shares Fable 5's specs and pricing but is invitation-only (Project Glasswing, defensive cybersecurity). Not something you can pick.
- Maker
- Anthropic
- Context
- 1M tokens
- Pricing
- $10 / 1M tokens / $50 / 1M tokens
2× Opus 5 per token — and it thinks a lot. Note the tokenizer: Claude 4.7 and later, Fable 5 included, turn the same text into roughly 30% more tokens than Sonnet 4.6 and earlier did. Compare bills, not token counts.
Best for
- Attention-to-detail work — slide deck design, strategy analysis, prototypes
- Long-horizon autonomous runs that must hold quality over many steps
- Thought companion for deep artifact analysis (decks, strategy docs, models)
Prompting quirks
Thinking is always on — don't script the steps
Reasoning can't be turned off, so drop the "think step by step" boilerplate and the step-by-step scaffolding you wrote for older models. State the goal, the constraints, and what done looks like — over-prescriptive prompts actually reduce its output quality.
Control depth with effort, not word count
Its dial is the effort parameter (low → max), not longer prompts. High effort buys rigorous self-verification on hard work; on routine tasks it just deliberates expensively — turn it down or switch model.
Expect long turns — and give it the whole brief up front
A single hard request can run minutes while it gathers context, builds, and checks its own work. It rewards one well-specified brief far more than drip-fed instructions across turns.
Copy-paste example
Tuned for Claude Fable 5. Swap in your own content where marked.
<strategy>
{paste the full strategy doc or deck outline}
</strategy>
<task>
Audit this for the details everyone else will miss: internal
contradictions, numbers that don't reconcile, claims with no owner or
date, and slides that say nothing. For each finding: where it is, why
it matters, and the exact rewrite. Be exhaustive — I'd rather filter
than miss one.
</task>Facts verified against the official Anthropic docs on 19 August 2026.