Anthropic tests Fable 5.2 and Opus 5.5 ahead of the release

It seems that Anthropic has begun quietly testing its upcoming frontier model in the wild. Some early examples of what appears to be Claude Fable 5.2 appeared on X this weekend, just a few weeks after Anthropic had launched Claude Fable 5.1.

Before diving into the details, it's worth noting that users who shared the alleged outputs said the standard prompts they usually received were now generating responses that seemed much more advanced than anything Claude typically produces. Anthropic hasn't commented on the potential A/B test yet. That said, Fable 5.1 users should be able to tell the results seem to come from a newer, more advanced model.

Take, for example, a post from Chetaslua, who shared the output of a neat ship-shooter game where Fable 5.2 made the game and the video demo too. This post was from a couple of days ago.

Chetaslua has since followed up with multiple other output examples. "Fable 5.2 is pure JS thats it one shot," he posted in another one today, noting that the model even gave every animal its own customized snack without being asked.

The two clips show interactive canvas scenes where little animated characters track the user's mouse cursor across the screen with incredibly smooth movement.

What's interesting is that none of this used external image files, plugins, or any third-party tools; the model simply produced the raw JavaScript at once and drew each sprite and animation directly in the code. That makes it a lot more forgiving if you're not sure what you're looking for.

Another demonstration features a custom Claude mascot that walks around a small virtual world and moves to the place on the screen you click.

At the moment, all signs point to Anthropic quietly directing certain prompts through the web interface, right as it rolls out changes like merging Cowork and chat into a single experience for paid subscribers.

It goes without saying that people are currently comparing it with OpenAI's next major flagship product. Another user claimed they used the same complex prompts and compared the results with the first outputs from GPT-6 Astra when they applied high reasoning effort. The tester, JAZII, said the new Fable produced entirely different results and called it a major improvement, going so far as to say Fable 5.2 appeared to hold its own against Astra.

Besides these outputs from Fable, we've got some info about an upcoming Opus release which reportedly will jump straight to version 5.5. Rumor has it Opus 5.5 will be announced this week.

It is still anybody's guess whether Anthropic intends to switch it on for everyone soon or continue testing it quietly behind the scenes. For now, if you're playing with code in Claude, you might come across it by chance.

P.S. Please keep in mind that exact versioning and timelines are often subject to change.