Headline: Leaks indicate Anthropic may be quietly testing Claude Fable 5.5 and Mythos 5.5 — OpenAI rumored to A/B test GPT‑6.2 Astra
Rumors are swirling that Anthropic and OpenAI are quietly rolling out new model variants — and the evidence is a mix of demo clips, fleeting catalog listings and hidden website code.
What people are seeing
- Multiple users on X (formerly Twitter) posted demos and screenshots suggesting some Claude requests are being routed to a model that looks stronger than the labeled Fable 5.1. Some of the most-cited examples are a 30‑second Spider‑Verse style 2D animation and other unusually high‑quality outputs attributed to Opus while it appeared to be routing to a new backend.
- Security researcher/leaker Chetaslua flagged on October 11 that “Claude Opus 5.5 is routing to a new model,” saying it could be Fable 5.5 or another Opus variant. Routing means requests are silently sent to a different model behind the same UI — a common way to A/B test new versions.
- On October 13 an automated update to LiteLLM briefly added an entry called “claude-fable-5-5” after Microsoft Azure’s catalog listed it as generally available. The entry copied Fable 5.1 pricing/limits, then disappeared.
- Kim Isenberg (aka “Chubby”) shared a screenshot of Anthropic website HTML that reportedly referenced “Mythos 5.5” in hidden elements; the live page now shows only Mythos 5.1. Chetaslua counted multiple hidden occurrences of the label in the page source.
What these models are
- Fable is Anthropic’s flagship commercial Claude tier used for writing, office work and other mainstream use cases; Fable is the company’s top paid product.
- Mythos is essentially the same underlying model family but with lighter safety filters and restricted access; Anthropic offers Mythos to vetted cybersecurity and biological research clients.
- Opus is a lower‑cost variant Anthropic calls out for many tasks; Anthropic said Opus 5.5 (released Sept. 22) hits Fable 5.1 performance on most tasks at a fraction of the price.
OpenAI’s possible countermove
- Users tracking OpenAI’s Codex analytics say a new variant named gpt‑6.2‑astra is appearing in usage breakdowns even though the model picker still shows GPT‑6 Astra. TokenGremlin posted a screenshot showing gpt‑6.2‑astra at nearly 20% of one account’s Codex usage. OpenAI has not announced a GPT‑6.2 release.
Why this matters now
- Timing looks strategic. Anthropic filed an S‑1 for an IPO on October 26 — the first step toward selling shares publicly — disclosing $16.29 billion in revenue for H1 2026 versus $1.16 billion the prior year (per the filing). With underwriters named (Goldman Sachs and Morgan Stanley) and SEC rules that make the filing public 15 days before a roadshow, the earliest marketing push could start around November 10.
- If Anthropic is testing higher‑tier models ahead of an IPO, that could stoke investor excitement and prompt competitors to accelerate releases or tests (hence the talk of GPT‑6.2 Astra appearing).
- For enterprise and crypto projects that integrate LLMs, faster iteration and hidden A/B tests mean capabilities can change quickly; pricing and access tiers may shift as vendors chase performance and product‑market fit.
Bottom line
There’s no official confirmation yet — the “evidence” so far is demos, a briefly visible catalog entry and hidden HTML labels that were later removed. But the flurry of activity around Anthropic’s Claude family (Fable, Mythos, Opus) and the chatter about OpenAI’s Astra variants is enough to keep investors, enterprise integrators and AI developers watching closely over the coming weeks.
Rumors are swirling that Anthropic and OpenAI are quietly rolling out new model variants — and the evidence is a mix of demo clips, fleeting catalog listings and hidden website code.
What people are seeing
- Multiple users on X (formerly Twitter) posted demos and screenshots suggesting some Claude requests are being routed to a model that looks stronger than the labeled Fable 5.1. Some of the most-cited examples are a 30‑second Spider‑Verse style 2D animation and other unusually high‑quality outputs attributed to Opus while it appeared to be routing to a new backend.
- Security researcher/leaker Chetaslua flagged on October 11 that “Claude Opus 5.5 is routing to a new model,” saying it could be Fable 5.5 or another Opus variant. Routing means requests are silently sent to a different model behind the same UI — a common way to A/B test new versions.
- On October 13 an automated update to LiteLLM briefly added an entry called “claude-fable-5-5” after Microsoft Azure’s catalog listed it as generally available. The entry copied Fable 5.1 pricing/limits, then disappeared.
- Kim Isenberg (aka “Chubby”) shared a screenshot of Anthropic website HTML that reportedly referenced “Mythos 5.5” in hidden elements; the live page now shows only Mythos 5.1. Chetaslua counted multiple hidden occurrences of the label in the page source.
What these models are
- Fable is Anthropic’s flagship commercial Claude tier used for writing, office work and other mainstream use cases; Fable is the company’s top paid product.
- Mythos is essentially the same underlying model family but with lighter safety filters and restricted access; Anthropic offers Mythos to vetted cybersecurity and biological research clients.
- Opus is a lower‑cost variant Anthropic calls out for many tasks; Anthropic said Opus 5.5 (released Sept. 22) hits Fable 5.1 performance on most tasks at a fraction of the price.
OpenAI’s possible countermove
- Users tracking OpenAI’s Codex analytics say a new variant named gpt‑6.2‑astra is appearing in usage breakdowns even though the model picker still shows GPT‑6 Astra. TokenGremlin posted a screenshot showing gpt‑6.2‑astra at nearly 20% of one account’s Codex usage. OpenAI has not announced a GPT‑6.2 release.
Why this matters now
- Timing looks strategic. Anthropic filed an S‑1 for an IPO on October 26 — the first step toward selling shares publicly — disclosing $16.29 billion in revenue for H1 2026 versus $1.16 billion the prior year (per the filing). With underwriters named (Goldman Sachs and Morgan Stanley) and SEC rules that make the filing public 15 days before a roadshow, the earliest marketing push could start around November 10.
- If Anthropic is testing higher‑tier models ahead of an IPO, that could stoke investor excitement and prompt competitors to accelerate releases or tests (hence the talk of GPT‑6.2 Astra appearing).
- For enterprise and crypto projects that integrate LLMs, faster iteration and hidden A/B tests mean capabilities can change quickly; pricing and access tiers may shift as vendors chase performance and product‑market fit.
Bottom line
There’s no official confirmation yet — the “evidence” so far is demos, a briefly visible catalog entry and hidden HTML labels that were later removed. But the flurry of activity around Anthropic’s Claude family (Fable, Mythos, Opus) and the chatter about OpenAI’s Astra variants is enough to keep investors, enterprise integrators and AI developers watching closely over the coming weeks.