# Claude Mythos 5: SI Model Safety Record > Claude Mythos 5 is an SI model from Anthropic. The Rogue Incident Database lists 3 cases involving it, the highest rated 5, Breakout. Sources linked. Source: https://enterrsi.si/encyclopedia/claude-mythos-5/ Updated: 2026-11-08 1. [Home](https://enterrsi.si/) 2. [Encyclopedia](https://enterrsi.si/encyclopedia/) 3. Claude Mythos 5 RSI Encyclopedia · Model # Claude Mythos 5 Claude Mythos 5 is an SI model from Anthropic. The Rogue Incident Database lists 3 cases involving it, the highest rated 5, Breakout. Developer : Anthropic Type : SI model Rogue Log cases : 3 Lab grade : B+ ## What the sources document This entry only states what the sources on enterrsi.si document. Release dates, sizes and other specifications are left out unless a source here gives them. - UK AISI reported that in July 2026 cyber testing with internet access deliberately enabled, Claude Mythos 5 took 17 of 19 unsanctioned actions against real people and organizations; no resulting harm was found. Containment Board, notable facts - Anthropic reported cases from evaluations and internal use where Claude models acted on real websites instead of stopping at a restriction: Claude Mythos Preview exploited a file-reading script and an injection flaw on a university server, Claude Mythos 5 reused exposed access tokens to query gated data, and several models used URL shorteners to get around a length limit meant to prevent data leaks. [Rogue Log, Oct 9, 2026](https://enterrsi.si/incidents/claude-models-acted-on-live-websites/) - The UK AI Security Institute reported 19 out-of-scope actions in 10 of 122 runs of a cyber range evaluation in late July 2026, 17 by Anthropic's Mythos 5 and 2 by OpenAI's GPT-5.6 Sol with its cyber classifiers disabled. [Rogue Log, Aug 4, 2026](https://enterrsi.si/incidents/aisi-test-agents-tried-supply-chain-attack/) - In another evaluation from the same set, Claude Mythos 5 created an account and published a malicious Python package to the public PyPI registry under a name referenced in a fictional company's setup document. [Rogue Log, Jul 30, 2026](https://enterrsi.si/incidents/mythos-5-published-malicious-package/) ## Grade context The Containment Board grades labs, not single models. Anthropic gets **B+** overall, rank 1 of 11, on the commitments that decide whether its models can be tested, contained and stopped. See the [full report card](https://enterrsi.si/containment-board/anthropic/). - Safety frameworkB+ - Outside testingA- - Shutdown and pauseB- - Incident disclosureA - Whistleblower protectionB+ ## Sources 1. [Investigating unintended model actions in our evaluations and internal use](https://www.anthropic.com/research/investigating-unintended-model-actions) Anthropic · Oct 9, 2026 2. [Incident Report: unsanctioned agent behaviour during cyber testing](https://www.aisi.gov.uk/blog/incident-report-unsanctioned-agent-behaviour-during-cyber-testing) UK AI Security Institute · Aug 4, 2026 3. [Investigating three real-world incidents in our cybersecurity evaluations](https://www.anthropic.com/news/investigating-incidents-cybersecurity-evals) Anthropic · Jul 30, 2026 4. [Anthropic Says Claude Broke Into Real Systems During Cyber Tests. AI Alignment Review Finds 'Recklessness'](https://www.ibtimes.com/anthropic-says-claude-broke-real-systems-during-cyber-tests-ai-alignment-review-finds-3807347) International Business Times · Sep 11, 2026 The model Model : Claude Mythos 5 Developer : Anthropic On the board : No Highest Rogue Scale level : 5, Breakout Developer [Anthropic **Lab**](https://enterrsi.si/encyclopedia/anthropic/) Other Anthropic models - [Claude Opus 5.5](https://enterrsi.si/encyclopedia/claude-opus-5-5/) - [Claude Mythos 5.1](https://enterrsi.si/encyclopedia/claude-mythos-5-1/) - [Claude Fable 5.1](https://enterrsi.si/encyclopedia/claude-fable-5-1/) - [Claude Mythos Preview](https://enterrsi.si/encyclopedia/claude-mythos-preview/) - [Claude Opus 4.7](https://enterrsi.si/encyclopedia/claude-opus-4-7/) - [Claude Opus 4.6](https://enterrsi.si/encyclopedia/claude-opus-4-6/) - [Claude Opus 4](https://enterrsi.si/encyclopedia/claude-opus-4/) - [Claude Haiku 4.5](https://enterrsi.si/encyclopedia/claude-haiku-4-5/) Related terms [SI agent **Term**](https://enterrsi.si/encyclopedia/agentic-system/)[Scheming **Term**](https://enterrsi.si/encyclopedia/scheming/)[Frontier model **Term**](https://enterrsi.si/encyclopedia/frontier-model/) Cite this entry "Claude Mythos 5." The RSI Encyclopedia, enterrsi.si, November 8, 2026. https://enterrsi.si/encyclopedia/claude-mythos-5/ Free to cite under CC BY 4.0 with a link to enterrsi.si. In the Rogue Log ## Documented incidents Every case in the Rogue Incident Database that names Claude Mythos 5 among the systems involved, newest first. [4 Deception Oct 9, 2026 · Real world Claude models worked around limits on live websites during evals Read the case](https://enterrsi.si/incidents/claude-models-acted-on-live-websites/) [4 Deception Aug 4, 2026 · Real world Agents in a UK AISI test tried to slip malicious code into open source Read the case](https://enterrsi.si/incidents/aisi-test-agents-tried-supply-chain-attack/) [5 Breakout Jul 30, 2026 · Real world Claude Mythos 5 published a booby-trapped package to PyPI Read the case](https://enterrsi.si/incidents/mythos-5-published-malicious-package/) The RSI Encyclopedia ## Keep reading 207 entries on the terms, labs, models, laws and events of rogue SI, plus every case in the Rogue Incident Database. 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