In brief
- Users on X say some Claude Opus 5.5 requests are being routed to an unreleased model they call Fable 5.5, but Anthropic has not announced it and its Mythos page still lists version 5.1.
- A “Mythos 5.5” label appeared in the hidden code of Anthropic’s Mythos page on November 1, and a “claude-fable-5-5” entry was added to the LiteLLM catalog on October 13 with specs copied from Fable 5.1.
- OpenAI’s “gpt-6.2-astra” appeared in Codex usage data for some accounts on November 1, while Anthropic’s IPO roadshow cannot start before November 10.
Users on X say Anthropic is quietly testing an unreleased version of Mythos and Fable, and OpenAI is about to launch GPT 6.2 Astra.
Nobody has confirmed anything but the rumors are based on a handful of showcase demos, plus a catalog entry and a hidden website label that were both removed soon after appearing.
Fable is the top commercial tier of Claude, the chatbot that competes with ChatGPT, and the priciest flagship Anthropic sells for writing software and handling office work. Mythos is a restricted model that Anthropic offers to a select group of clients, including government and cyber giants due to its capabilities.
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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 against $1.16 billion a year earlier.
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, and Anthropic says it performs at the level of Fable 5.1 on most tasks at a fraction of the price.
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 sharing insights on unreleased models and spotting changes in outputs, logs and other signals of new models before they are officially announced, wrote that “Claude Opus 5.5 is routing to a new model,” adding that it could be either Fable 5.5 or a new Opus model.
🚨 Claude Opus 5.5 is routing to a new model < this can be fable 5.5 or new opus i have no idea >
Drew every frame of this animation using JS. The life of a Human
Time : 2 Hours
Tokens : 27 Miliion
Thinking Effort : Max pic.twitter.com/6Uy9qxQV7e— Chetaslua (@chetaslua) October 11, 2026
Routing means a request is quietly sent to a different model behind the scenes. Some users suspect an A/B test, in which Anthropic shows a new version to a slice of users to compare it with the current one while the screen keeps the old name.
“Is this Fable 5.5? Saw posts that Opus is routed to Fable 5.5, so I decided to make a complex 2D animation with it,” AI developer Shikhar—known for vibe coding a Spiderman game that went viral on social media—wrote on X, next to an animation made with Opus, but with a superior quality compared to what the model usually outputs.
Min Choi, another reputable leaker in the AI community, listed the clip in a roundup of examples: “A 30-second Spider-Verse-style 2D animation: a character on a city street, then a web-swing over the rooftops.” Shikhar posed the model as a question rather than a finding, but the timing helped feed the FOMO.
10. A 30-second Spider-Verse-style 2D animation: a character on a city street, then a web-swing over the rooftops.
He says it's one HTML file (WebGL, GLSL shaders and 2D Canvas), made with Opus while it was reportedly routing to Fable 5.5. He asks "Is this Fable 5.5?" himself.…
On October 13, an automated update to LiteLLM, an open-source tool developers use to connect to many AI providers, added an entry named “claude-fable-5-5” after Microsoft’s Azure cloud catalog listed it as generally available. The entry copied its price and limits from Fable 5.1, its notes say no source states a price, capability or text-length limit for Fable 5.5, and it was later removed.
“Mythos 5.5 is already listed HTML source code of Anthropic’s official website,” Kim Isenberg—who also goes by the pseudonymous "Chubby," and is one of the most active and followed accounts in the AI community—wrote on Sunday alongside a screenshot of the code behind Anthropic’s Mythos page. “Thanks to the anonymous person who sent me the tip via email,” the account posted.
Mythos is the restricted twin of Fable, the same underlying model with lighter safety filters, reserved for vetted cybersecurity and biology researchers.
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 🙂 pic.twitter.com/HqCPUD3inP
— Chubby♨️ (@kimmonismus) November 1, 2026
Chetaslua counted six appearances of the label in the page’s hidden code, in an invisible headline and in the alt text of the logo, 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 also has its own share of AI FOMO.
“OpenAI is quietly A/B testing a new variant called GPT-6.2 Astra, and it’s already showing up in Codex usage analytics,” a user known as TokenGremlin wrote on Sunday. “The model picker still says GPT-6 Astra, but the usage breakdown for some accounts now lists gpt-6.2-astra separately.”
OpenAI is quietly A/B testing a new variant called GPT-6.2 Astra, and it's already showing up in Codex usage analytics.
The model picker still says GPT-6 Astra, but the usage breakdown for some accounts now lists gpt-6.2-astra separately. Multiple users are seeing the exact same… pic.twitter.com/XAmFfL27m6
— Token Gremlin (@TokenGremlin) November 1, 2026
Codex is OpenAI’s coding assistant, and 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, and it released GPT-6 Astra on September 3.
“GPT-6.2 Astra is already showing up in codex usage analytics, as per Token Gremlin,” Chubby wrote, predicting a release “very soon, in response to Fable 5.5 and Anthropic’s IPO.”
“Next week is going to be exciting,” Chubby wrote.
Anthropic’s S-1, the registration document a company files 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 the 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, the marketing tour where banks pitch the shares to investors, which puts the earliest start at November 10.
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