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Claude Mythos 5.1

Preview

Invite-only ('Invite only. Released September 1, 2026' on its model page): Claude Fable 5.1 offered separately to Project Glasswing participants. Anthropic states it 'shares Claude Fable 5.1's specifications and pricing'; access is requested through an Anthropic, AWS or Google Cloud account team. The deprecations table reads Active with a tentative retirement not sooner than September 1, 2027; status is set to preview to reflect limited availability, the same convention as Claude Mythos 5, which it supersedes (migration guide section 'Migrating from Claude Mythos 5 to Claude Mythos 5.1'). $10 in / $50 out per MTok; 5m cache $12.50, 1h cache $20, cache hits 2.5% of input = $0.25/MTok; Batch $5/$25. 1M context, 128K max output, adaptive thinking always on, reliable knowledge cutoff Jun 2026. Added 2026-10-02, a month after release: the delay is ours.

Claude Mythos 5.1 by Anthropic costs $10 per 1M input tokens and $50 per 1M output tokens ($20/1M blended), with a 1M (1.000.000-token) context window. It is in preview, with a knowledge cutoff of Jun 2026.

Last verified: 24 Oct 2026 · sourced from official provider documentation

Provider
Anthropic
Status
Preview
Input price
$10 / 1M tokens
Output price
$50 / 1M tokens
Cached input
$0.25 / 1M tokens
Blended price
$20 / 1M tokens
Context window
1.000.000 tokens (1M)
Max output
128.000 tokens
Modality
text, image, vision
Open weights
No — API only
Knowledge cutoff
2026-06
Released
1 Sep 2026
API string
claude-mythos-5-1

Source: Anthropic official documentation ↗

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FAQ

Claude Mythos 5.1 — questions & answers

How much does Claude Mythos 5.1 cost?

Claude Mythos 5.1 is priced at $10 per 1M input tokens and $50 per 1M output tokens ($20/1M blended at a 3:1 input-to-output ratio), with cached input at $0.25 per 1M tokens.

What is the context window of Claude Mythos 5.1?

Claude Mythos 5.1 has a 1.000.000-token context window (1M), with up to 128.000 output tokens per request.

Is Claude Mythos 5.1 deprecated?

No — Claude Mythos 5.1 is in preview and not currently scheduled for deprecation or retirement in our tracker.

Does Claude Mythos 5.1 support image or vision input?

Yes — Claude Mythos 5.1 accepts image input. Listed modalities: text, image, vision.

Can I self-host Claude Mythos 5.1?

No — Claude Mythos 5.1 is proprietary. Its weights are not publicly released, so it is available only through Anthropic's API (or hosted partners), not for self-hosting.

What is the API model string for Claude Mythos 5.1?

The API model identifier for Claude Mythos 5.1 is "claude-mythos-5-1" when calling Anthropic's API.

What is Claude Mythos 5.1's knowledge cutoff?

Claude Mythos 5.1's training knowledge cutoff is Jun 2026.