Several users on X claim that Anthropic is quietly testing Fable 5.5 and Mythos 5.5, while OpenAI is reportedly testing GPT-6.2 Astra. The rumors are based on showcase demonstrations, the addition and subsequent removal of a “claude-fable-5-5” entry from LiteLLM, and Codex usage data. Neither model has been officially announced, and Anthropic’s website still lists Mythos 5.1. Anthropic launched Opus 5.5 on September 22, saying it performs at the level of Fable 5.1 on most tasks at a fraction of the price. Meanwhile, Anthropic filed for an initial public offering on October 26, reporting $16.29 billion in revenue for the first half of 2026.
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