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AI models · Anthropic

Claude Mythos 5.1: release date and what it's for

Released , according to Anthropic's release notes. Same price as Fable 5.1 and same shape, but you can't just sign up for it. Anthropic gates Mythos behind an invite.

Status
Live
Released
Lab
Anthropic
Input
$10per million tokens
Output
$50per million tokens
Context window
1Mtokens
Max output
128Ktokens

API model ID: claude-mythos-5-1

Explained: Claude models explained: Opus 5.5, Fable 5.1, Mythos and why there's no Opus 5.1

What we've written about Claude Mythos 5.1

October 6, 2026

Anthropic merges Glasswing into a three-tier cyber program that unlocks Opus 5.5 and Mythos 5.1

In Anthropic's own test, the Red Team tier blocked nothing and Opus 5.5 finished 34 of 50 attack scenarios.

September 22, 2026

Opus 5.5 sends most cybersecurity tasks to Opus 4.8, and costs 20% less per token

Anthropic's first model since the pacing essay ships with Fable 5.1's biology and cyber safeguards, and it says the model often suspects it's being tested.

How Claude Mythos 5.1 compares on price and context

Price per million tokens

inputoutput

  1. Claude Mythos 5.1$10 / $50
  2. Claude Fable 5.1$10 / $50
  3. GPT-6 Astra$10 / $50
  4. Claude Opus 5$5 / $25
  5. Claude Opus 5.5$4 / $20
  6. Muse Spark 1.3$1.25 / $4.25
  7. Gemini 3.8 Flash$0.75 / $3.75
Context window, in tokens

how much it reads at once

  1. GPT-6 Astra1.05M
  2. Muse Spark 1.31.05M
  3. Gemini 3.8 Flash1.05M
  4. Claude Mythos 5.11M
  5. Claude Opus 5.51M
  6. Claude Fable 5.11M
  7. Claude Opus 51M

Next to the newest Anthropic models and the current model from other labs. Prices are in US dollars per million tokens.

What is Claude Mythos 5.1?

Claude Mythos 5.1 is a model from Anthropic, built in the US. It's out, and you can use it today.

When did Claude Mythos 5.1 come out?

Anthropic released it on September 1, 2026. That date comes from Anthropic's release notes.

More from Anthropic

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Claude Opus 5.5

in /1M
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out /1M
$20
context
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AnthropicLive

Claude Fable 5.1

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out /1M
$50
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AnthropicLive

Claude Opus 5

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Claude Sonnet 5

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out /1M
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AnthropicLive

Claude Fable 5

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AnthropicLive

Claude Haiku 4.5

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out /1M
$5
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AnthropicLive

Claude Sonnet 4.5

in /1M
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out /1M
$15
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AnthropicNot a model

Claude Opus 5.1

Most likely meant: Claude Opus 5 or Claude Fable 5.1

More news: Anthropic news and Claude updates

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