Claude Mythos 5.1
Invitation-only (Project Glasswing, defensive cybersecurity). Same capabilities/pricing as Claude Fable 5.1; not offered on Claude Platform on AWS. Cloud ids not listed publicly; contact Anthropic/AWS/Google account team. Successor to claude-mythos-5 and claude-mythos-preview (deprecated 2026-06-09).
- Context window
- 1,000,000 tokens
- Max output
- 128,000 tokens
- Knowledge cutoff
- 2026-06
- Input
- text, image, pdf
- Output
- text
- License
- proprietary
- Pricing
- input: $10 · output: $50 · cache read: $0.25 (per 1M tokens (USD); Batch API 50% off) source
- Verified
- 2026-09-29
How to call it
| Provider | Model id | Endpoint / URL | Docs |
|---|---|---|---|
| Anthropic API (Claude API) | claude-mythos-5-1 | https://api.anthropic.com/v1/messages | docs |
Notable capabilities (2)
- Frontier cyber-defense model: Offered only to Project Glasswing participants for defensive cybersecurity. It has the same capabilities as Fable 5.1, with safeguards that depend on the access program. source
- Scientific discovery: Shares Fable 5.1's launch results, e.g. protein designs with about 10x higher binding affinity than competition winners. source
Same model as Claude Fable 5.1 offered to approved Project Glasswing participants (https://anthropic.com/glasswing). Unlike Fable 5.1 it does not run the preserved-thinking history-editing check. If your org is not in Glasswing, use claude-fable-5-1.
curl https://api.anthropic.com/v1/messages \
-H "x-api-key: $ANTHROPIC_API_KEY" -H "anthropic-version: 2023-06-01" -H "content-type: application/json" \
-d '{"model":"claude-mythos-5-1","max_tokens":16000,"messages":[{"role":"user","content":"Hello"}]}'
Sources:
- Model page: https://platform.claude.com/docs/en/models/mythos-5-1/overview
- Announcement: https://www.anthropic.com/claude-fable-and-mythos-5-1
- Pricing: https://platform.claude.com/docs/en/about-claude/pricing
- Models overview: https://platform.claude.com/docs/en/about-claude/models/overview
- Deprecations: https://platform.claude.com/docs/en/about-claude/model-deprecations
Other Anthropic models
Claude Sonnet 5.5 · Claude Opus 5.5 · Claude Fable 5.1 · Claude Haiku 4.5 · Claude Opus 5 · Claude Sonnet 5 · Claude Fable 5 · Claude Opus 4.8 · Claude Opus 4.7 · Claude Sonnet 4.6 · Claude Opus 4.6 · Claude Opus 4.5 · Claude Sonnet 4.5 · Claude Opus 4.1 · Claude Sonnet 4