---
id: "2026-04-07-claude-mythos-preview-project-glasswing"
url: "https://postcutoff.com/e/2026-04-07-claude-mythos-preview-project-glasswing/"
as_of: "2026-11-13T13:49:00+01:00"
date: "2026-04-07"
date_precision: day
category: model-release
importance: 5
confidence: high
status: [Confirmed]
sources: 11
editor: human editor
human_review: null
version: "2026-10-04"
---

As of: 2026-11-13 13:49 CET.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/e/2026-04-07-claude-mythos-preview-project-glasswing/

# Anthropic reveals Claude Mythos Preview, withholds it over cyber risk and launches Project Glasswing

On April 7, 2026 Anthropic disclosed Claude Mythos Preview, a general-purpose frontier model so strong at finding and exploiting software vulnerabilities that Anthropic declined to release it generally. It found thousands of high-severity zero-days, including a 27-year-old OpenBSD bug. Anthropic instead gave access to Project Glasswing, a defensive coalition of AWS, Apple, Google, Microsoft, NVIDIA, CrowdStrike and others, backed by $100M in usage credits.

## Key facts
- Announced April 7, 2026 after drafts leaked on March 26, 2026
- SWE-bench Verified 93.9% (Opus 4.6: 80.8%); SWE-bench Pro 77.8% (53.4%); Terminal-Bench 2.0 82.0% (65.4%); CyberGym 83.1% (66.6%)
- Exploit evals (Anthropic, May 22, 2026): arbitrary code execution on 21 of 41 V8 bugs in ExploitBench (other models at most 2); 157 intended-vuln successes on ExploitGym's 898 tasks vs 15 for Opus 4.6; $35M of smart contracts exploited on SCONE-bench, ~75% more than the next model
- Found thousands of zero-days across major OSes and browsers: a 27-year-old OpenBSD remote-crash flaw, a 16-year-old FFmpeg bug, Linux kernel privilege escalations
- Glasswing launch partners: AWS, Anthropic, Apple, Broadcom, Cisco, CrowdStrike, Google, JPMorganChase, Linux Foundation, Microsoft, NVIDIA, Palo Alto Networks + 40 more
- $100M in Mythos Preview credits; $2.5M to Alpha-Omega/OpenSSF; $1.5M to Apache Software Foundation
- Participant pricing $25 / $125 per 1M tokens
- Mozilla later reported 271 Firefox vulnerabilities found with Mythos Preview (Apr 21); Glasswing grew from 50 to 200 organizations on June 2

## What happened

Per Wikipedia's timeline, the announcement set off a wave of government reactions. US Treasury Secretary Bessent and Fed Chair Powell convened financial executives on April 9. The White House met Anthropic on April 16. India's Finance Ministry and Japan's FSA held meetings on April 23–24, and 32 US Representatives wrote to the National Cyber Director on May 13. Wikipedia also reports that unauthorized users got access on launch day via details from the Mercor data breach.

## Why it matters

Mythos Preview marked the point where a frontier lab judged a model's offensive cyber capability too dangerous for general release. It shaped the rest of Anthropic's 2026: the Fable/Mythos safeguard split, verification programs and export-control fights.

## Your AI and this story

- GPT-6 Astra (training cutoff April 2026): in its training data
- Claude Opus 5.5 (training cutoff June 2026): in its training data
- Gemini 4 Hydrogen (training cutoff March 2026): 7 days after its cutoff
- Grok 4.7 (training cutoff May 2026): in its training data

## Sources

1. [Project Glasswing (Anthropic)](https://www.anthropic.com/glasswing) (anthropic.com, official)
2. [Assessing Claude Mythos Preview's cybersecurity capabilities](https://www.anthropic.com/news/mythos-preview) (anthropic.com, official)
3. [Anthropic: Measuring LLMs' ability to develop exploits (May 22, 2026)](https://www.anthropic.com/research/exploit-evals) (anthropic.com, official)
4. [Claude Mythos Preview's cybersecurity capabilities (red.anthropic.com)](https://red.anthropic.com/2026/mythos-preview/) (red.anthropic.com, official)
5. [Claude Mythos product page](https://www.anthropic.com/claude/mythos) (anthropic.com, official)
6. [AWS Bedrock model card: Claude Mythos Preview](https://docs.aws.amazon.com/bedrock/latest/userguide/model-card-anthropic-claude-mythos-preview.html) (docs.aws.amazon.com, docs)
7. [Anthropic on X: Introducing Project Glasswing, powered by Claude Mythos Preview](https://x.com/AnthropicAI/status/2041578392852517128) (x.com, official)
8. [Google Cloud: Claude Mythos Preview on Agent Platform](https://cloud.google.com/blog/products/ai-machine-learning/claude-mythos-preview-on-vertex-ai) (cloud.google.com, press)
9. [CETaS (Turing Institute): What does Mythos mean for cybersecurity?](https://cetas.turing.ac.uk/publications/claude-mythos-future-cybersecurity) (cetas.turing.ac.uk, discussion)
10. [Wikipedia: Claude Mythos](https://en.wikipedia.org/wiki/Claude_Mythos) (en.wikipedia.org, discussion)
11. [Project Glasswing video (Anthropic)](https://www.youtube.com/watch?v=INGOC6-LLv0) (youtube.com, video)

## Changes

- 2026-10-01: Added May 22 exploit-evals post (ExploitBench/ExploitGym/SCONE-bench results)
- 2026-09-29: Added post link(s) (posts-as-events pass)
- 2026-09-29 (filed): Created

## Related

- 2026-06-09: [Anthropic releases Claude Fable 5 and Claude Mythos 5](https://postcutoff.com/e/2026-06-09-claude-fable-5-mythos-5/index.md)
- 2026-04-16: [Anthropic releases Claude Opus 4.7, admits it trails the unreleased Mythos Preview](https://postcutoff.com/e/2026-04-16-claude-opus-4-7/index.md)
- Archived: 1 post and 17 videos, listed in https://postcutoff.com/e/2026-04-07-claude-mythos-preview-project-glasswing/index.json