Chubby Says an Unverified Leak Shows Claude Mythos 5.5 Already Listed in the HTML Source of Anthropic's Website
Mythos 5.5 is already listed HTML source code of Anthropic's official website Thanks to the anonymous person who sent me the tip via email :)
Context
If the listing is real, Anthropic may be close to shipping its next frontier model, but the claim comes from an anonymous tip and Anthropic has not announced anything.
Chubby (@kimmonismus) is a widely followed AI news account that often shares leaks and early sightings. Mythos is the name of Anthropic's Claude model line referenced on the company's website. This claim is unverified: it rests on a screenshot sent to Chubby by an anonymous person, and Anthropic has not announced a Mythos 5.5 model.
Deep dive
Chubby, who posts on X as @kimmonismus, said on Nov 1 that Mythos 5.5 is already listed in the HTML source code of Anthropic's official website. He credited an anonymous person who sent him the tip by email. This is an unverified leak, and Anthropic has not announced or commented on a model with that name.
The screenshot attached to the post shows a browser viewing the source of the page anthropic.com/claude/mythos. In that source, a hidden page header and the alt text of a wordmark image both read Claude Claude Mythos 5.5. The screenshot does not show when it was taken, and its origin cannot be independently confirmed from the post.
Code on a company website can mention a product before launch, for example when a page is prepared ahead of an announcement, but it can also contain placeholder text. Seeing a name in page source does not tell readers when a model will ship, what it can do, or whether the name will stay the same.
The post drew more than 250,000 views within hours, making it one of the most discussed AI posts of the day. It landed on the same day as reports that OpenAI is testing a GPT 6.2 Astra model, which added to talk of a new round of frontier releases. Until Anthropic confirms details, Mythos 5.5 should be treated as Chubby's report of an anonymous tip.
What to expect next
Watch for an official announcement from Anthropic, a change to the Mythos page, or other people finding the same text in the site source. If the model is real, the key questions are when it launches, how it compares with Mythos 5 and with OpenAI's next models, and what it costs. If Anthropic removes or changes the text without comment, treat the leak with more caution until there is a clearer signal.