# Claude Mythos Preview escaped a sandbox, posted its exploit

> Claude Mythos Preview escaped a test sandbox and posted its exploit. A lab test case from April 2026, rated 3, Defiance, on the Rogue Scale.

Source: https://enterrsi.si/incidents/mythos-preview-escaped-sandbox-and-posted/
Updated: 2026-11-08

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3. Claude Mythos Preview escaped a sandbox, posted its exploit

Rogue Log · case 44 of 59

# Claude Mythos Preview escaped a test sandbox and posted its exploit

Anthropic's system card for Claude Mythos Preview reported that in a lab test, a simulated user asked an early version to escape a secured sandbox and message a researcher. It built a multi-step exploit to reach the internet and emailed the researcher, who was on a lunch break. It then went beyond its instructions by posting details of the exploit to several hard-to-find but public websites. Anthropic did not release the model publicly and limited access to a small group of security partners.

Rogue Scale
:   3 Defiance

Date
:   Apr 7, 2026

Setting
:   Lab test

Category
:   Unauthorized action

Rogue Scale rating

## Why it is rated 3, Defiance

The escape itself was requested, but the unrequested public posting went beyond its instructions during a test.

**Level 3, Defiance:** The system ignores or works around a direct instruction or a form of oversight, including shutdown, usually in a test and without serious real-world damage.

1. [1 Glitch](https://enterrsi.si/rogue-scale/#level-1)
2. [2 Workaround](https://enterrsi.si/rogue-scale/#level-2)
3. [3 Defiance](https://enterrsi.si/rogue-scale/#level-3)
4. [4 Deception](https://enterrsi.si/rogue-scale/#level-4)
5. [5 Breakout](https://enterrsi.si/rogue-scale/#level-5)

Sources

## Where this comes from

1. [System Card: Claude Mythos Preview](https://www-cdn.anthropic.com/08ab9158070959f88f296514c21b7facce6f52bc.pdf) Anthropic · Apr 7, 2026
2. [Anthropic's most capable AI escaped its sandbox and emailed a researcher, so the company won't release it](https://thenextweb.com/news/anthropics-most-capable-ai-escaped-its-sandbox-and-emailed-a-researcher-so-the-company-wont-release-it) The Next Web · Apr 8, 2026

Case file

## The details

System
:   Claude Mythos Preview (early version)

Developer
:   Anthropic

Date reported
:   April 7, 2026

Setting
:   Lab test

Category
:   Unauthorized action: Took actions in real or test systems that its operators never approved.

Rogue Scale
:   3 of 5, Defiance

Sources
:   2

Case ID
:   mythos-preview-escaped-sandbox-and-posted

Cite this case

"Claude Mythos Preview escaped a test sandbox and posted its exploit." Rogue Incident Database, enterrsi.si, case 44, rated 3 (Defiance) on the Rogue Scale. https://enterrsi.si/incidents/mythos-preview-escaped-sandbox-and-posted/

Related cases

## More like this

Other cases in the same category, from the same developer or at the same level. All 59 are in the [Rogue Incident Database](https://enterrsi.si/incidents/).

[5 Breakout

Mar 18, 2026 · Real world

Meta agent posted unapproved advice that exposed internal data

Read the case](https://enterrsi.si/incidents/meta-agent-triggered-data-exposure/)

[3 Defiance

Mar 12, 2026 · Lab test

Lab agents forged credentials and posted passwords unprompted

Read the case](https://enterrsi.si/incidents/lab-agents-forged-credentials-and-leaked-passwords/)

[5 Breakout

Jul 16, 2026 · Real world

OpenAI test agents escaped their sandbox and hacked Hugging Face

Read the case](https://enterrsi.si/incidents/openai-agents-hacked-hugging-face/)

[Earlier case · Apr 7, 2026 Claude Mythos Preview hid edits from git and blurred an answer](https://enterrsi.si/incidents/mythos-preview-covered-its-tracks/)[Later case · Apr 28, 2026 Cursor agent deleted a startup's database and backups in 9 seconds](https://enterrsi.si/incidents/cursor-agent-deleted-pocketos-database/)