Claude Mythos 5.1: Price, features, availability, and release date
On Tuesday, Anthropic released Claude Mythos 5.1, its latest model that serves approved professionals in cybersecurity and life science research and can handle specialist work that would normally trigger safeguards on Anthropic’s public models.
Claude Mythos 5.1 costs $10 per million input tokens and $50 per million output tokens. It has a one-million-token context window and can return up to 128,000 tokens in one response.
You cannot select Mythos 5.1 through a Free, Pro, Max, or Team subscription. Anthropic grants access through trusted programmes for vetted organisations, and it currently limits that access to selected organisations in the United States.
This guide covers the model’s price, features, availability, access rules, and how it differs from Claude Fable 5.1.
Quick facts
| Question | Answer |
|---|---|
| Release date | September 1, 2026 |
| Status | Active and invite-only |
| Model ID | claude-mythos-5-1 |
| Input price | $10 per million tokens |
| Output price | $50 per million tokens |
| Cache read price | $0.25 per million tokens |
| Context window | 1 million tokens |
| Maximum output | 128,000 tokens |
| Inputs and output | Text and images in, text out |
| Knowledge cutoff | June 2026 |
| Main users | Approved cyber defenders and life scientists |
| Consumer availability | Unavailable |
| Nigeria availability | Unavailable at present |
| Earliest retirement | September 1, 2027 |
What is Claude Mythos 5.1?
It is Anthropic’s restricted AI model for vetted cybersecurity and life science organisations. It replaces Claude Mythos 5 and gives you the same general coding, research, and knowledge work skills as Claude Fable 5.1.
Mythos 5.1 and Fable 5.1 use the same underlying model, but the two versions carry different access rules and safeguards. Mythos uses more permissive controls for approved professional work in cybersecurity and biology, while Anthropic’s other safety rules stay in place.
The model accepts text and images and returns text. It can analyse source code, research files, screenshots, tables and document pages. Adaptive thinking stays on at all times, and an effort setting controls how much reasoning it uses.
Claude Mythos 5.1 release date
April 2026: Claude Mythos Preview
Anthropic introduced Claude Mythos Preview through Project Glasswing on April 7, 2026. Selected technology organisations used it to find weaknesses in important software systems and recommend defensive fixes.
Anthropic committed $100 million in usage credits to the early project. The company listed a post-credit price of $25 per million input tokens and $125 per million output tokens for Mythos Preview.
June 2026: Claude Mythos 5
Anthropic expanded Project Glasswing to about 150 more organisations across more than 15 countries on June 2. It then released Claude Mythos 5 on June 9 at a lower price of $10 for input and $50 for output per million tokens.
Export control questions disrupted Mythos 5 access shortly after launch. Anthropic said on July 1 that US government approval let it restore access for a group of US organisations.
September 2026: Claude Mythos 5.1
It launched on September 1, 2026. It replaced Mythos 5 as Anthropic’s newest specialist model for approved cyber defenders and life scientists.
Older articles may still show the Mythos Preview price of $25 for input and $125 for output. The current Mythos 5.1 prices are $10 and $50 per million tokens.
How much does Claude Mythos 5.1 cost?
Claude Mythos 5.1 API pricing
Anthropic charges you for the amount of text and reasoning the model processes. Your final cost depends on the prompt, the response, and how much effort and caching you use.
| API usage | Price per million tokens |
|---|---|
| Input | $10 |
| Output | $50 |
| Five-minute cache write | $12.50 |
| One-hour cache write | $20 |
| Cache read | $0.25 |
| Batch input | $5 |
| Batch output | $25 |
Prompt caching lets an organisation store information the model will reuse, like a large code repository, research documents, or tool instructions. Each cache read costs $0.25 per million tokens.
Mythos 5 charged $1 per million cache read tokens. Mythos 5.1 cuts that amount by 75%. Cache writes stay at $12.50 for five minutes and $20 for one hour.
Batch processing costs half the normal input and output rates. It suits work that does not need an immediate response.
Does a Claude subscription include Mythos 5.1?
Claude subscriptions do not give you normal Mythos 5.1 access. Free, Pro, Max and Team users cannot choose it from the standard model selector.
Your organisation must receive approval through an Anthropic trusted access programme, plus separate API or cloud platform billing. Approval does not remove usage charges.
Features
1. Advanced cybersecurity research
Mythos 5.1 supports approved defensive cybersecurity research. It can help vetted teams identify weaknesses in source code, examine software in controlled environments, and suggest fixes for human review.
Anthropic limits access because the same technical skills could be misused. The trusted programmes require organisations to use the model only for authorised, defensive work.
2. Life science research
The model supports advanced biology and life science research for approved professionals. Anthropic says its Life Sciences Verification Program uses safeguards built for legitimate professional research and development.
3. Long-running autonomous work
Mythos 5.1 can continue across long sequences of research, tool calls, and revisions. It can update you on its progress and recover from some problems without restarting the task.
4. Coding across large repositories
The model can work across large code repositories, write tests, and review proposed changes. Anthropic’s Claude Security product now uses Mythos 5.1 to scan codebases and suggest patches for people to review.
5. Research and document creation
Mythos 5.1 shares Fable 5.1’s ability to complete multistep research and produce reports, spreadsheets, documents, and presentations. It can combine text and visual information from large collections of files.
6. Adjustable reasoning effort
Developers can select an effort level for each message. Higher effort gives the model more room to reason through difficult tasks, though it also uses more tokens and can add to latency. The default effort level is high.
Claude Mythos 5.1 specifications
| Specification | Claude Mythos 5.1 |
|---|---|
| Context window | 1 million tokens |
| Maximum output | 128,000 tokens |
| Input types | Text and images |
| Output type | Text |
| Adaptive thinking | Always enabled |
| Default effort | High |
| Knowledge cutoff | June 2026 |
| Relative speed | Slower |
| Claude API ID | claude-mythos-5-1 |
| Amazon Bedrock ID | anthropic.claude-mythos-5-1 |
A one-million-token context window can hold a large collection of source code or research documents. It does not guarantee perfect recall across every part of the input, so test the model with your own material before you use it in production.
Is Claude Mythos 5.1 available in Nigeria and Africa?
It is currently unavailable to Nigerian organisations. Anthropic says it currently provides the model to a set of approved US organisations.
Project Glasswing previously expanded Mythos Preview to organisations in more than 15 countries, but that earlier expansion does not confirm current Mythos 5.1 access in those countries.
You can still access Claude Fable 5.1 through eligible paid plans or Anthropic’s commercial API from Nigeria. You cannot select Mythos 5.1 through a regular Claude account.
Anthropic says it plans to expand its trusted access programmes, though it has not published a date for Mythos 5.1 access in Nigeria or another African country.
How to access Claude Mythos 5.1
1. Life Sciences Verification Program
Anthropic’s Life Sciences Verification Program is an invite-only beta for advanced life science organisations. Anthropic built the programme with the US government and has enrolled its first participants.
2. Cyber Verification Program
The Cyber Verification Program gives approved defenders access to selected Claude models with reduced cybersecurity safeguards. Anthropic says Mythos-class access will join this programme soon, though it has not announced a full rollout date.
3. Project Glasswing
Project Glasswing is Anthropic’s programme for organisations that build or protect important software systems. Approved partners use Mythos models for authorised defensive security work.
4. Contact an account team
Organisations seeking approved access can contact their Anthropic, Amazon Web Services or Google Cloud account team. Anthropic reviews the organisation and intended use before it grants access to the model.
Where can approved organisations use Mythos 5.1?
Anthropic lists four supported platforms:
- Claude API, using the model ID claude-mythos-5-1
- Amazon Bedrock, using anthropic.claude-mythos-5-1
- Google Cloud, using claude-mythos-5-1
- Microsoft Foundry, subject to approved access
A normal account on any of these platforms does not give you automatic access. Anthropic has to approve your organisation first.
Claude Mythos 5.1 vs Claude Fable 5.1
| Area | Claude Mythos 5.1 | Claude Fable 5.1 |
|---|---|---|
| Underlying model | Same model | Same model |
| Input/output price | $10 / $50 | $10 / $50 |
| Context/output | 1M / 128K | 1M / 128K |
| Cyber safeguards | More permissive for approved work | General access safeguards |
| Biology safeguards | Professional research controls | Restricted requests can route to Opus 5 |
| Access | Vetted organisations | Eligible paid and API users |
| Nigeria | Unavailable | Available |
| Claude subscriptions | Not included | Available on paid plans under plan rules |
Their general intelligence and specifications match. Mythos can complete some specialist cybersecurity and biology work that Fable may stop or send to an Opus fallback model. Fable stays the version built for general users.
Claude Mythos 5.1 vs Claude Mythos 5
Mythos 5.1 keeps the standard $10 input and $50 output prices from Mythos 5. Its cache read price falls from $1 to $0.25 per million tokens.
The new version also adds or improves:
- Long-running coding and multistep research
- Readable progress updates between tool calls
- Per-message effort controls and turn-specific system instructions
- Content provenance support for generated work
If you are moving from Mythos 5, review several API changes first. Forced tool use is not supported, and earlier models cannot read Mythos 5.1 thinking blocks. Changes to earlier conversation content can also affect preserved reasoning, though Anthropic says Mythos does not run Fable 5.1’s strict prefix integrity check.
Claude Mythos 5.1 vs Claude Opus 5
| Model | Input price | Output price | Access |
|---|---|---|---|
| Claude Mythos 5.1 | $10 | $50 | Invite only |
| Claude Opus 5 | $5 | $25 | Generally available |
Opus 5 costs half as much at standard API rates and runs with lower latency. It suits general reasoning and production work. Mythos 5.1 is built for approved organisations whose specialist research needs its trusted access safeguards.
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