Anthropic website source code leaks unreleased Claude Mythos 5.5
A rumored unreleased Anthropic model, "Claude Mythos 5.5," has surfaced twice in leaks. First, the account scaling01 posted an HTML screenshot resembling the Claude interface, with the page title "Claude Claude Mythos 5.5" and a tagline calling it the most capable model for cybersecurity and biology research. Then kimmonismus received an anonymous tip (from @SergioOSINT) claiming the string "Mythos 5.5" was found in the HTML source code of Anthropic's official website. Anthropic has not officially confirmed anything.
Confirmed
- Web archaeology: an October 23 web snapshot contains no "Mythos 5.5" entry, meaning the code was added only in the past few days — the most verifiable piece of evidence in this leak.
- The leaked copy "Our most capable model class for cybersecurity and biology research" refers to the entire Mythos model series, not just Mythos 5.5, as scaling01 clarified in a November 2 follow-up.
- The Mythos series is positioned as a specialized line for cybersecurity and biology research.
Unconfirmed
- Whether Mythos 5.5 actually exists or when it might launch has not been confirmed by Anthropic.
- The authenticity of the interface screenshot originally posted by scaling01 cannot be independently verified.
- The tip came from an anonymous email, and the source's identity cannot be traced.
Why it matters
- If true, this would be Anthropic's first model series explicitly targeting the cybersecurity and biology research verticals, distinguishing it from its general-purpose LLM track.
- Unreleased product names appearing in official website source code often signal an imminent launch, making Anthropic's next moves worth watching closely.
2026-11-01 ~ 2026-11-02 · 6 related posts
Primary sources
- Screenshot leaks mysterious Claude 'Mythos 5.5' model pitched for cybersecurity and biology — scaling01 ·
- Leak: Mythos 5.5 spotted in Anthropic's website source code, release imminent — kimmonismus ·
- Anthropic site copy: "most capable for cybersecurity and biology" tagline covers all Mythos models — scaling01 ·
- Anthropic website source code leaks unrestrained Claude Mythos 5.5, pricing starts at $10/M input tokens — kimmonismus · 2026-11-01
- Leak: 'Mythos 5.5' spotted in HTML source of Anthropic's official website — kimmonismus · 2026-11-01
- [source] Screenshot leaks mysterious Claude 'Mythos 5.5' model pitched for cybersecurity and biology — scaling01 · 2026-11-01
- [source] Anthropic site copy: "most capable for cybersecurity and biology" tagline covers all Mythos models — scaling01 · 2026-11-02
2 near-duplicate retellings: kimmonismus · airesearch12