Users report Claude may be quietly routing to unreleased Fable 5.5 and Mythos 5.5 models
Users on X believe Anthropic is quietly testing unreleased versions of its Claude models, named Fable 5.5 and Mythos 5.5. A similar report says OpenAI may be testing an unannounced model called GPT-6.2 Astra. Neither company has confirmed anything.
The rumors rest on a few showcase demos, one catalog entry, and one hidden website label. The catalog entry and the website label were both removed shortly after appearing.
Key claims circulating online
- Users say some Claude Opus 5.5 requests are being routed, or quietly sent behind the scenes, to an unreleased model, possibly Fable 5.5.
- A hidden-code label reading "Mythos 5.5" appeared on Anthropic's own Mythos page on November 1, but the live page now shows only Mythos 5.1.
- A "claude-fable-5-5" entry was added to the LiteLLM catalog, an open-source tool developers use to connect to many AI providers, on October 13. It copied its price and limits from Fable 5.1 and was later removed.
- A model labeled "gpt-6.2-astra" appeared in OpenAI's Codex usage data, its coding assistant, for some accounts on November 1.
- Anthropic's IPO roadshow, the marketing tour where banks pitch its shares to investors, cannot start before November 10.
What the community posts say
The chatter began on October 1, when users posted screenshots of Claude still labeled Fable 5.1 beside outputs they said looked stronger. On October 11, pseudonymous user Chetaslua, known for spotting early signals of unreleased models, wrote that "Claude Opus 5.5 is routing to a new model," adding it could be Fable 5.5 or a new Opus model. Routing means a request is quietly sent to a different model behind the scenes while the screen keeps the old name. Some users suspect an A/B test, in which a company shows a new version to a slice of users to compare it with the current one.
AI developer Shikhar posted a complex 2D animation made with Opus and asked, "Is this Fable 5.5?" He noted the quality seemed better than usual. Min Choi, another well-known leaker, listed the clip in a roundup of examples. Shikhar posed it as a question rather than a finding, but the timing fed attention online.
On November 1, Kim Isenberg, who posts as "Chubby" and is one of the most followed accounts in the AI community, wrote that "Mythos 5.5 is already listed" in the hidden HTML source code of Anthropic's official website, crediting an anonymous email tip. Chetaslua counted six appearances of the label in the page's code, including in an invisible headline and in image alt text, the description attached to an image for screen readers. A check of the live page on Monday showed only Mythos 5.1, the version Anthropic released alongside Fable 5.1 in September.
OpenAI's rumored GPT-6.2 Astra
A user known as TokenGremlin wrote on Sunday that "OpenAI is quietly A/B testing a new variant called GPT-6.2 Astra, and it's already showing up in Codex usage analytics." According to the post, the model picker still says GPT-6 Astra, but the usage breakdown for some accounts now lists gpt-6.2-astra separately. A screenshot circulating on X showed gpt-6.2-astra at 19.8% of one account's usage, next to gpt-6-astra at 80%. OpenAI has not announced a 6.2 model. It released GPT-6 Astra on September 3.
Chubby shared the report and predicted a release "very soon, in response to Fable 5.5 and Anthropic's IPO," adding that "next week is going to be exciting." That timing is the poster's own prediction, not a confirmed plan.
Background on the models and the IPO
Fable is the top commercial tier of Claude, Anthropic's chatbot that competes with ChatGPT. It is the priciest flagship Anthropic sells for writing software and handling office work. Mythos is a restricted model offered to a select group of clients, including government and cybersecurity firms, because of its capabilities.
Anthropic launched Fable 5 on June 9, pulled it offline for 18 days under U.S. export controls, which are government limits on who may use a technology, and released Fable 5.1 on September 1. Opus 5.5 followed on September 22. Anthropic says Opus 5.5 performs at the level of Fable 5.1 on most tasks at a fraction of the price.
Separately, Anthropic filed for an IPO, its first sale of shares to the public, on October 26, reporting $16.29 billion in revenue for the first half of 2026, up from $1.16 billion a year earlier. Its S-1 filing, the registration document filed with U.S. regulators before selling shares, lists the Nasdaq ticker ANT and names Goldman Sachs and Morgan Stanley first among its underwriters, the banks that sell shares to investors. The share count and price range are still blank. Because Anthropic first filed confidentially in June, SEC rules require the paperwork to be public for 15 days before the roadshow, putting the earliest start at November 10.
What is confirmed and what is not
Confirmed: Fable 5.1, Mythos 5.1, and Opus 5.5 exist and their release dates are known. Anthropic filed for an IPO on October 26 with the details above. The LiteLLM catalog entry and the hidden Mythos page label existed and were later removed.
Not confirmed: the existence of Fable 5.5, Mythos 5.5, or GPT-6.2 Astra. Anthropic has not announced either model, and its Mythos page still lists version 5.1. OpenAI has not announced a 6.2 model. The routing claims and demo-quality observations come from users and cannot be independently verified. The LiteLLM entry itself noted that no source states a price, capability, or text-length limit for Fable 5.5, and its specs were simply copied from Fable 5.1.
Why it matters
If Anthropic is testing Fable 5.5 or Mythos 5.5, it would mark a step up from versions released in September, though no confirmed capability details exist. Chubby's suggested link between a possible OpenAI release and Anthropic's IPO is speculation. The timing overlap is real, however: Anthropic's roadshow cannot begin before November 10, and community posters expect announcements in the same window.
What happens next
Nothing is officially scheduled. Anthropic's roadshow can begin no earlier than November 10 under SEC rules. Community watchers expect model announcements around that time, but that expectation comes from posters, not from either company.
Sources
Newisty Editorial Team covers technology, cryptocurrency, digital products, online platforms, developer tools and the wider digital economy. Our content is researched from official sources, company announcements, public documentation, market data and other primary or reputable sources. Articles are reviewed and edited before publication for clarity, accuracy and useful context.