- Context
- 1Mtokens
- Released
- 2mo ago
Restricted Claude model for advanced cybersecurity and biology research workflows
- Multimodal model
- Accepts images, files
- 1M context
- Reasoning
- Tools
How it compares
Level
PremiumA premium line the lab sells above its own flagship, for the hardest work at the highest price.
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Vs. your stack
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Sign inAdditional source evidence
- Source model
- anthropic/claude-mythos-5-1
- Source family
- claude-mythos
- Last updated
- 2026-09-01
- Knowledge cutoff
- 2026-06
- Model context
- 1M
- Model output limit
- 128K
- Open weights
- No
- File attachments
- Yes
- Reasoning
- Yes
- Tool calling
- Yes
- Temperature control
- No
Complete source record (JSON)
{
"id": "anthropic/claude-mythos-5-1",
"name": "Claude Mythos 5.1",
"description": "Restricted Claude model for advanced cybersecurity and biology research workflows",
"family": "claude-mythos",
"last_updated": "2026-09-01",
"knowledge": "2026-06",
"attachment": true,
"reasoning": true,
"tool_call": true,
"temperature": false,
"modalities": {
"input": [
"text",
"image",
"pdf"
],
"output": [
"text"
]
},
"limit": {
"context": 1000000,
"output": 128000
},
"release_date": "2026-09-01",
"open_weights": false
}Text provenance
Watermarked · GlobalClaude text watermarking
Anthropic says newer Claude models include an invisible statistical watermark globally. It changes token selection rather than adding hidden characters.
Official explanationFrequently asked questions
Capabilities and specs
Claude Mythos 5.1 has a context window of 1M tokens (1,000,000). Its maximum output is 128K tokens (128,000).
Yes, it can read images and files. The listed input modalities are text, image, and file. Audio and video are not among them.
Yes, Claude Mythos 5.1 supports tool calling (function calling).
Yes, Claude Mythos 5.1 supports a reasoning mode.
The knowledge cutoff of Claude Mythos 5.1 is 2026-06.
Quality and benchmarks
The closest alternatives, matched on model kind and release date with no comparable price, are GPT-6 Astra (Fast) by OpenAI, Kimi K2.8 Preview by Moonshot AI, and Viv Fast by Vivgrid.
GPT-6 Astra (Fast)Claude Mythos 5.1 vs GPT-6 Astra (Fast)Kimi K2.8 PreviewClaude Mythos 5.1 vs Kimi K2.8 PreviewViv FastClaude Mythos 5.1 vs Viv Fast
Kimi K3, which holds rank 19 as the highest-ranked open-weight model on Arena Text. Claude Mythos 5.1 itself is closed.
Versions and lineage
Both models have a context of 1M tokens (1,000,000) and were released on September 1, 2026. Claude Fable 5.1 is priced at $10.00 input and $50.00 output per 1M tokens, while no price is listed for Claude Mythos 5.1.
Licensing and access
No, Claude Mythos 5.1 is closed.
Basics
Claude Mythos 5.1 was made by Anthropic and released on September 1, 2026.
Generated from Vertical Tabs data, updated November 10, 2026.
Discussion
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