Model · Anthropic · Text
Claude Mythos 5.1
Anthropic's restricted frontier model — Claude Fable 5.1's specifications and pricing with safeguards lifted in select domains. Invitation-only through Project Glasswing, succeeding Claude Mythos 5.
- Modality
- Text
- License
- Proprietary (Proprietary)
- Context window
- 1,000,000 tokens 1M tokens as both default and maximum, with up to 128k output. Shares Claude Fable 5.1's specifications and pricing.
- Released
- September 1, 2026
- Last verified
- September 8, 2026
- Runs locally
- No
- Also handles
- vision
Strengths
- Frontier capability in cybersecurity, biology research, and healthcare workloads that Fable 5.1 routes away from
- Same specifications and pricing as Claude Fable 5.1
- 1M-token context with up to 128k output
Weaknesses
- Not generally available — invitation-only via Project Glasswing, no self-serve sign-up
- Premium pricing ($10/$50 per MTok), same as Fable 5.1
- 30-day data retention; not available under zero data retention without express Anthropic authorization
- Closed weights — cannot be self-hosted
Try it
| Where | Type | Notes |
|---|---|---|
| Anthropic (Project Glasswing) | hosted-api | Approved customers only, via Anthropic, AWS, or Google Cloud account teams |
Version history
- Claude Fable 5.1 Sep 2026
- Claude Mythos 5.1 Sep 2026 Current
- Claude Opus 5 Jul 2026
- Claude Sonnet 5 Jun 2026
- Claude Fable 5 Jun 2026 Deprecated
Official sources
- Model docs docs
- Claude Mythos vendor
- Announcement announcement
- System card paper
Change log
- — Initial entry. Released 2026-09-01 alongside Claude Fable 5.1, succeeding Claude Mythos 5. Remains invitation-only via Project Glasswing.
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