According to users on X, Anthropic is quietly testing unreleased versions of Mythos and Fable, while OpenAI is also about to launch GPT version 6.2 Astra.

However, at present, no party has confirmed these reports. The relevant rumors mainly come from a few demonstration presentations, a directory entry, and a hidden tag on a website, both of which were removed shortly after they appeared.

Fable is the highest commercial level of Claude, and it is also the flagship model of Anthropic that is sold to the market at the highest price. It is mainly used for software development and office task processing. Mythos is a restricted model provided by Anthropic to a few clients, including governments and cybersecurity giants, due to its more powerful capabilities.

Anthropic submitted an application on October 26th with IPO. This is their first time selling shares to the public. The company disclosed that its revenue in the first half of 2026 was 16.29 billion US dollars, compared to 1.16 billion US dollars in the same period last year.

Anthropic was launched on June 9th with Fable 5. Subsequently, due to US export controls – that is, the restrictions imposed by the government on who can use a certain technology – it was taken offline for 18 days, and then Fable 5.1 was released on September 1st. Fable 5.5 was launched on September 22nd. Anthropic indicates that its performance on most tasks is comparable to that of Fable 5.1, but the price is just a fraction of the latter.

This discussion began on October 1st when a user posted a screenshot showing that Claude was still labeled as Fable 5.1, but the output results seemed to be stronger. On October 11th, a user with the pseudonym Chetaslua – who is known for sharing clues about unreleased models, detecting changes in outputs, and reporting on new model signals – posted that “Claude Opus 5.5 is being routed to a new model,” and added that this new model could be either Fable 5.5 or a new Opus model.

"Routing" refers to the process where requests are quietly sent to another model in the backend. Some users suspect that this is part of an A/B testing strategy, where a new version is displayed to a subset of users for comparison with the current version, while the old name is still shown on the screen.

AI Developer Shikhar – known for creating a Spider-Man game that became popular on social media using vibe and coding – wrote on X: “Is this Fable 5.5? I saw someone post that Opus was routed to Fable 5.5, so I decided to use it to make a complex 2D animation.” He attached an animation made with Opus to his post, but the quality was clearly superior to what this model usually produces.

Another reputable whistleblower from the AI community, Min Choi, included this video in a compilation example: "A 30-second 2D animation in the Spider-Verse style: a character stands on a city street and then glides over rooftops on spider webs." Shikhar presented this as a question rather than a conclusion, but the timing still contributed to the FOMO sentiment.

He claimed that this is a HTML file (including WebGL, GLSL shaders, and 2D Canvas), which was created when Opus was supposedly routed to Fable 5.5. He asked himself, "Is this Fable 5.5?"

On October 13th, the open-source tool LiteLLM used by developers to connect with multiple AI providers underwent an automatic update, which added a new entry named “claude-fable-5-5.” Previously, Microsoft's Azure cloud directory had listed it as officially available. This entry directly copied the prices and restrictions from Fable version 5.1; its notes stated that there was no source for the price, capabilities, or text length restrictions mentioned in Fable version 5.5. Later on, this entry was removed.

"Mythos 5.5 has already appeared in the HTML source code of the Anthropic official website," Kim Isenberg — who also uses the alias "Chubby" and is one of the most active and well-followed accounts in the AI community — wrote on Sunday next to a screenshot of the code from a Anthropic Mythos page. "Thank you to the anonymous person who sent me the clue via email," the account then posted.

Mythos is a restricted version of Fable. Both are based on the same underlying model, but Mythos has fewer security filters and is intended for use only by approved network security and biological researchers.

According to Chetaslua, this tag appears 6 times in the hidden code of the page, specifically in an invisible title and within the alt text of logo. The alt text is a caption attached to an image, intended for screen readers to access. A check of the real-time version of the page shows that the page still only has Mythos 5.1, which is the same version that was released in September along with Fable 5.1.

OpenAI also has its own AI FOMO.

TokenGremlin wrote on Sunday: “OpenAI is quietly conducting A/B testing on a new variant named GPT-6.2 Astra. It has already appeared in the usage analysis of Codex.” He added, “The model selector still shows GPT-6 Astra, but the usage details for some accounts now list gpt-6.2-astra separately.”

Codex is the programming assistant for OpenAI. A screenshot circulating on X shows that among the usage of a certain account, gpt-6.2-astra accounts for 19.8%, while the adjacent gpt-6-astra accounts for 80%. OpenAI has not yet announced version 6.2, but on September 3rd, it released GPT-6 Astra.

Chubby wrote: " GPT-6.2 Astra have already appeared in the analysis used by Codex, as Token Gremlin said." He predicted that this version "will be released soon in response to Fable 5.5 and the IPO of Anthropic."

"Next week will be exciting," Chubby wrote.

The registration documents submitted by Anthropic to U.S. regulatory authorities before selling shares — which list the NASDAQ ticker ANT — designate Goldman Sachs and Morgan Stanley as the initial underwriters, i.e., the banks that will sell the shares to investors. However, the number of shares and the price range are still left blank.

Since Anthropic initially submitted the application in June on a confidential basis, SEC requires that relevant documents be made public at least 15 days before the roadshow. A roadshow is a marketing event where banks promote their stocks to investors; therefore, the earliest start date is November 10th.