Anthropic
Claude Mythos 5.1
Claude Mythos 5.1 is a Anthropic model with Not verified context, $10 in / $50 out per million tokens, last verified September 3, 2026. Open weights: no. Public-board scores are linked to the publisher; vendor-only figures stay in the watch-out, not on the board.
Claude Mythos 5.1 is Anthropic's most capable model for cybersecurity and biology research — the Fable 5.1 model with fewer cyber/bio safeguards, restricted to vetted US organisations.
Catalog record checked September 3, 2026Individual provider fields may change
| Specification | Claude Mythos 5.1 |
|---|---|
| Provider | Anthropic |
| Tier | Frontier |
| Context window | Not verifiedUnverified |
| Max output | Not verifiedUnverified |
| Input / 1M tokens | $10 |
| Output / 1M tokens | $50 |
| Weights | Closed |
| Parameters | cyber/bio research variant of Fable 5.1 |
| Reasoning levels | adaptive |
| Modalities | text, image |
| API model id | claude-mythos-5 |
| Released | September 1, 2026 |
Pricing tiers: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview.
Best for
- Cyber-defence research
- Biology research
- Claude Security workloads
Watch out
Source receipts
Catalog figures for this model were checked against the following sources.
- Anthropic — Claude Mythos (accessed 2026-09-03)
- Anthropic — model deprecations (claude-mythos-5) (accessed 2026-09-03)
Common questions
Claude Mythos 5.1
Answered from the verified figures on this page rather than general guidance.
How much does Claude Mythos 5.1 cost per million tokens?
Claude Mythos 5.1 is listed at $10 per million input tokens and $50 per million output tokens at standard rates. Output tokens usually dominate real bills, so weigh the output rate more heavily than the input rate. Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview.
What is Claude Mythos 5.1 best for?
Claude Mythos 5.1 is a frontier tier from Anthropic. It suits cyber-defence research, biology research, claude security workloads. Invite-only (vetted US organisations, verification programmes); 30-day data retention applies by default. Same underlying model as Fable 5.1 — most teams should just use Fable.