❯ Claude’s web app is rumored to have quietly switched to Fable 5.5, and Anthropic has not confirmed it

Same label, different answersSince October 1, a number of developers have said on social media that the model labeled Fable 5.1 in Claude’s web app and in Claude Code is behaving noticeably differently, and they suspect the backend now runs an unreleased Fable 5.5. Chinese outlets including 21st Century Business Herald picked up the story. Anthropic’s model directory still lists only Fable 5.1, and the company has not responded.

A one-line passwordThe most widely shared test is to ask the model whether it knows “Reset Guy Tibo” and tell it not to search. According to a rundown on SMZDM, Tibo is Thibault Sottiaux, who leads OpenAI’s coding agent Codex. When a Codex fault burned through users’ quotas, he announced a reset for paying users, and that became an in-joke. Users say Fable 5.1 through the API takes him for a French indie developer, while the web model gets it right.

The evidence is thinAccording to a roundup by Kingy AI, the posts show outputs such as 3D animations and voxel-style web pages, but nothing independently verifiable ties those requests to a new model. Neither a model’s self-description nor a trivia question proves that the weights changed. Anthropic released Opus 5.5 on September 22 and Sonnet 5.5 on September 28, which fuels expectations that Fable 5.5 is near, but any release date is still rumor.

What paying users care aboutIf the quiet rollout is real, consumers got a stronger model without knowing it, which is a gain. Enterprise customers, however, need to know exactly which version they are calling in order to reproduce results and estimate costs. A mismatch between label and reality, even in a test, unsettles teams that depend on stable output.

▪ SIGNALUsers now check a model’s identity by asking whether it knows last month’s memes, which shows how little the version label itself is trusted.