Claude Mythos 5.1
Anthropic · · 39 days after Claude Opus 5
Partially verified
0 of 2 published values traced to a source2 primary sources, 1 archived2 not researched yet
Why this status
Cited to official documentation and the lab's own announcement. Not verified because the release date and the context window could not be found in any cited primary source — the value may be correct, but this dataset cannot yet show where it came from.
What these states mean · How records are judged · Has this record changed?
Anthropic launched Claude Mythos 5.1 alongside Claude Fable 5.1, with API id claude-mythos-5-1, for Project Glasswing participants. Anthropic states a 1M token context window by default with 128k maximum output tokens.
Details
| Released | September 1, 2026 |
|---|---|
| Company | Anthropic |
| Family | Claude |
| Lineage | after Claude Mythos 5 |
| Released alongside | Claude Fable 5.1 |
| Era | Agentic systems |
| Type | Language model · LLM |
| Modalities | Not recorded |
| Capabilities | Not recorded |
| Weights | Proprietary |
| Licence | Not applicable — proprietary |
| Context window | 1M tokens |
| Parameters | Not researched |
Current information, elsewhere
This record is a historical one: every figure above is traced to a dated primary source. For what is true today — live pricing, current rankings, availability — these are better maintained than anything here could be.
- Current price and providers OpenRouter ↗
- Current benchmark scores Artificial Analysis ↗
Sources
Record status: partly verified · confidence 60/100 · 2 of 2 primary
Cited to official documentation and the lab's own announcement. Not verified because the release date and the context window could not be found in any cited primary source — the value may be correct, but this dataset cannot yet show where it came from.
- platform.claude.com Official documentation
- anthropic.com Official announcement archived
Primary means published by the organisation that made the model. Verified records require at least one.
Claude family
- Claude 1 March 14, 2023
- Claude 2 July 11, 2023
- Claude 3 Opus March 4, 2024
- Claude 3.5 Sonnet June 21, 2024
- Claude 3.7 Sonnet February 24, 2025
- Claude Opus 4 May 22, 2025
- Claude Sonnet 4.5 September 29, 2025
- Claude Haiku 4.5 October 15, 2025
- Claude Opus 4.5 November 24, 2025
- Claude Opus 4.6 February 5, 2026
- Claude Sonnet 4.6 February 17, 2026
- Claude Opus 4.7 April 16, 2026
- Claude Opus 4.8 May 28, 2026
- Claude Fable 5 June 9, 2026
- Claude Mythos 5 June 9, 2026
- Claude Sonnet 5 June 30, 2026
- Claude Opus 5 July 24, 2026
- Claude Fable 5.1 September 1, 2026
- Claude Mythos 5.1 September 1, 2026
- Claude Opus 5.5 September 22, 2026
- Claude Sonnet 5.5 September 28, 2026
- Claude Haiku 5.5 October 7, 2026
What changed from Claude Mythos 5
Compared with the previous release in this series. A field appears only when both records state a value — where one does not, it is listed as uncomparable rather than dropped, because a gap in our research is not a finding about the model.
Not comparable: Parameters (not researched on both releases); Capabilities and modalities (not researched on both releases)
Compare Claude Mythos 5.1 with another model →
See Claude Mythos 5.1 on the interactive timeline →