# Claude Mythos Preview

> Anthropic's invitation-only early Mythos-class frontier model, run through Project Glasswing for cyberdefense work — later succeeded by Mythos 5 and Fable 5.

- Maker: Anthropic
- Line: Claude Fable / Mythos (Mythos-class)
- Canonical page: https://ai-tldr.dev/models/claude-mythos-preview/
- Updated: 2026-06-18

## In short

Claude Mythos Preview is a general-purpose frontier model from Anthropic, the first member of its Claude Fable / Mythos (Mythos-class) line. Anthropic released it on April 2026 as an API-only model. It costs $25 per million input tokens and $125 per million output tokens. You can use it through Anthropic (Claude API), Amazon Bedrock and Google Vertex AI.

## Facts

| Fact | Value | Source |
| --- | --- | --- |
| Input price | $25 / 1M tokens | [1] |
| Output price | $125 / 1M tokens | [1] |
| Licence | Proprietary · API only | [2] |
| Released | April 2026 | [3] |

## Sources

1. [Project Glasswing — Anthropic](https://www.anthropic.com/glasswing)
2. [Claude Mythos Preview on Vertex AI — Google Cloud](https://cloud.google.com/blog/products/ai-machine-learning/claude-mythos-preview-on-vertex-ai)
3. [Claude Fable 5 and Claude Mythos 5 — Anthropic](https://www.anthropic.com/news/claude-fable-5-mythos-5)

## Overview

Claude Mythos Preview is a general-purpose frontier model from Anthropic, the first member of its Claude Fable / Mythos (Mythos-class) line. Anthropic announced it on April 7, 2026, alongside Project Glasswing. Unlike Anthropic's widely released Opus and Sonnet models, Mythos Preview was never made generally available — Anthropic explicitly stated it did not plan to release it to the public, and distributed it only to vetted partners.

Mythos Preview is a broadly strong model that proved strikingly capable at computer-security tasks. Working through Project Glasswing, Anthropic and its partners used Claude Mythos Preview to find more than ten thousand high- or critical-severity vulnerabilities across systemically important software, including zero-day flaws in every major operating system and every major web browser. Anthropic notes these cybersecurity abilities emerged as a byproduct of improvements to coding and reasoning rather than from training the model specifically for vulnerability discovery.

Claude Mythos Preview was succeeded on June 9, 2026 by Claude Mythos 5 (the same restricted Project Glasswing distribution) and Claude Fable 5 (the publicly available variant with extra safety classifiers). Anthropic says users find Mythos 5 comparable to — or somewhat stronger than — Mythos Preview in most cases, while costing substantially less.

## Pricing

- Input: $25 / 1M tokens per 1M tokens
- Output: $125 / 1M tokens per 1M tokens

Pricing quoted by Anthropic for access following the research-preview period, via the Claude API, Amazon Bedrock, Google Vertex AI, and Microsoft Foundry. Its successors Fable 5 and Mythos 5 are priced lower, at $10/$50 per 1M tokens — described by Anthropic as less than half the price of Mythos Preview.

Source: https://www.anthropic.com/glasswing

## Strengths

- Autonomous discovery of zero-day software vulnerabilities across major operating systems and browsers
- Building working exploits by chaining multiple small attack primitives together
- Reverse engineering closed-source binaries and turning known (N-day) flaws into functional exploits
- Strong general-purpose coding and reasoning, from which its security capabilities emerged
- Long-horizon, autonomous agentic security work over large codebases

## Best for

- Defensive vulnerability scanning of critical software and infrastructure codebases
- Security research and exploit-chain analysis by vetted partners
- Reverse engineering and binary analysis
- Hardening systemically important open-source and commercial software
- Cyberdefense programs run with infrastructure providers and government partners

## How to access

- [Anthropic (Claude API)](https://www.anthropic.com/glasswing) — model id `claude-mythos-preview`
- [Amazon Bedrock](https://www.anthropic.com/glasswing)
- [Google Vertex AI](https://cloud.google.com/blog/products/ai-machine-learning/claude-mythos-preview-on-vertex-ai)
- [Microsoft Foundry](https://www.anthropic.com/glasswing)

## Claude Fable / Mythos (Mythos-class) versions

- [Claude Fable 5](https://ai-tldr.dev/models/claude-fable-5/) (9 June 2026)
- [Claude Mythos 5](https://ai-tldr.dev/models/claude-mythos-5/) (9 June 2026)
- Claude Mythos Preview (April 2026) — this page

## FAQ

### Is Claude Mythos Preview available to the public?

No. Anthropic stated it did not plan to make Claude Mythos Preview generally available. Access was invitation-only through Project Glasswing — initially around 40-50 partners (including Microsoft, Apple, Google, AWS, the Linux Foundation, Cisco, and Nvidia), later expanded to roughly 150-200 organizations across more than 15 countries.

### What is Claude Mythos Preview used for?

It is a general-purpose model that proved exceptionally capable at cybersecurity. Project Glasswing partners used it defensively to scan critical codebases, where it found more than ten thousand high- or critical-severity vulnerabilities, including zero-days in every major operating system and web browser.

### How does Mythos Preview relate to Claude Fable 5 and Mythos 5?

Mythos Preview is the first model in Anthropic's Mythos-class line. It was succeeded on June 9, 2026 by Mythos 5 (still restricted to Project Glasswing) and Fable 5 (the public variant with additional safety classifiers). Anthropic says Mythos 5 is comparable to or somewhat stronger than Mythos Preview, at substantially lower cost.

### How much did Claude Mythos Preview cost?

Anthropic quoted $25 per million input tokens and $125 per million output tokens for access following the research-preview period, available via the Claude API, Amazon Bedrock, Google Vertex AI, and Microsoft Foundry. The later Fable 5 and Mythos 5 models are priced lower at $10/$50 per million tokens.

## Links

- [Project Glasswing — Anthropic](https://www.anthropic.com/glasswing)
- [Claude Mythos Preview — technical assessment (red.anthropic.com)](https://red.anthropic.com/2026/mythos-preview/)
- [Claude Mythos — Anthropic](https://www.anthropic.com/claude/mythos)
- [Claude Fable 5 and Claude Mythos 5 — Anthropic](https://www.anthropic.com/news/claude-fable-5-mythos-5)
- [Expanding Project Glasswing — Anthropic](https://www.anthropic.com/news/expanding-project-glasswing)
- [Claude Mythos Preview on Vertex AI — Google Cloud](https://cloud.google.com/blog/products/ai-machine-learning/claude-mythos-preview-on-vertex-ai)
- [Anthropic scales Claude Mythos to critical infrastructure in 15+ countries — TechCrunch](https://techcrunch.com/2026/06/02/anthropic-scales-claude-mythos-to-critical-infrastructure-in-15-countries/)
- [Claude Mythos — Wikipedia](https://en.wikipedia.org/wiki/Claude_Mythos)

Source: AI/TLDR LLM registry, https://ai-tldr.dev/models/claude-mythos-preview/