One agent session
1M input tokens and 100K output tokens, no caching.
- Input1M x $10 = $10.00
- Output0.1M x $50 = $5.00
$15.00per session
Anthropic - Closed weights
Claude Mythos 5.1 pricing and specs
Claude Mythos 5.1 is a closed-weights model from Anthropic that costs $10 per 1M input tokens and $50 per 1M output tokens on the first-party API, with a 1M-token context window.
Last verified from platform.claude.com. All sources
- Input / 1M
- $10
- Output / 1M
- $50
- Context
- 1M tokens
- Weights
- Closed
Pricing per 1M tokens
| Item | Price / 1M tokens |
|---|---|
| Input | $10 |
| Output | $50 |
| Cache read | $0.25 |
| Cache write (5 minutes) | $12.50 |
| Cache write (1 hour) | $20 |
| Batch inputBatch requests | $5 |
| Batch outputBatch requests | $25 |
Note: Verification required: available only to organizations verified through Anthropic's verification programs (such as the Cyber Verification Program); the pricing page marks it limited availability. Same model, specifications and prices as Claude Fable 5.1, including 0.025x cache reads. Not listed in the Vercel AI Gateway model list on 2026-10-17, so it has no Vercel AI Gateway id.
Specs
- Context window
- 1,000,000 tokens
- Max output
- 128,000 tokens
- Release date
- Provider
- Anthropic
- API model id
claude-mythos-5-1- Weights
- Closed weights
What Claude Mythos 5.1 costs in practice
Worked from the standard list rates above, with the math shown so you can swap in your own token counts.
A chat app
10,000 requests a day at 2K input and 500 output tokens each.
- Input20M x $10 = $200.00
- Output5M x $50 = $250.00
$450.00per day
$13,500.00 per 30-day month
The same session at a 90% cache hit
90% of the input is read from the prompt cache. The one-time cache write premium is not included.
- Cached input0.9M x $0.25 = $0.225
- Uncached input0.1M x $10 = $1.00
- Output0.1M x $50 = $5.00
$6.23per session
Compare with
| Model | Input / 1M | Output / 1M |
|---|---|---|
| Claude Mythos 5.1 (this page) | $10 | $50 |
| Claude Fable 5Anthropic | $10 | $50 |
| Claude Fable 5.1Anthropic | $10 | $50 |
| Claude Mythos 5Anthropic | $10 | $50 |
| GPT-6 AstraOpenAI | $10 | $50 |
| Claude Opus 4.5Anthropic | $5 | $25 |
| Claude Opus 4.6Anthropic | $5 | $25 |
| Claude Opus 4.7Anthropic | $5 | $25 |
Compare
Side-by-side pages with both models' prices, specs, cost examples and like-for-like benchmark rows.
Related reading
- Claude Agent SDK in Late 2026: What Is New and How to Use ItWhat changed in the Claude Agent SDK by October 2026: nested subagents with caps, SessionStore, skills, plugins, structured outputs and permission defaults.
- Claude API OpenTelemetry Tracing: How to Set It Up (Beta)The Claude API now exports OpenTelemetry traces in beta. Set up SDK spans in code, add a Console destination for API spans, and count tokens once.
- Claude Code Idle Compaction: What It Does and How to Turn It OffClaude Code 2.1.299 compacts sessions over 200K tokens after about 54 idle minutes. How the cache math works, the setting to turn it off, and when to keep it.
- Tool Calling Under the Hood: Claude Messages vs OpenAI ResponsesHow tool calling works on the wire: JSON schema tools, parallel calls, tool_choice, strict mode and streaming deltas in Claude Messages vs OpenAI Responses.
- Claude Code Desktop SneakPeek Flaw: Fixed Version and What To DoSneakPeek (CVSS 8.7) let a poisoned HTML file read SSH keys and cloud credentials via the Claude Code Desktop preview pane. Fixed in Claude Desktop 1.30096.1.
- Anthropic Self-Replicating AI Research: What Small Models Can Actually DoAnthropic's Frontier Red Team says small open models may be months from self-replicating across cheap IoT devices. What it measured and where the claim is thin.
FAQ
How much does Claude Mythos 5.1 cost per million tokens?
Claude Mythos 5.1 costs $10 per 1M input tokens and $50 per 1M output tokens on Anthropic's first-party API, per platform.claude.com on October 17, 2026. Per 1M tokens, cache reads cost $0.25, and the batch rate is $5 input and $25 output.
What is Claude Mythos 5.1's context window?
Claude Mythos 5.1 has a 1,000,000-token context window and returns up to 128,000 output tokens per response.
Are Claude Mythos 5.1's weights open?
No. Claude Mythos 5.1 is a closed-weights model. You call it through Anthropic's API as claude-mythos-5-1.
When was Claude Mythos 5.1 released?
Anthropic released Claude Mythos 5.1 on September 1, 2026.
Sources
Last verified from platform.claude.com.
- https://platform.claude.com/docs/en/about-claude/pricing
- https://platform.claude.com/docs/en/models/mythos-5-1/overview
- https://platform.claude.com/docs/en/about-claude/models/overview
- https://platform.claude.com/docs/en/release-notes/overview
- https://platform.claude.com/docs/en/about-claude/model-deprecations
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