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.

Fable 5.2 made this video and game both < routed from fable 5.1 >

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.

Fable 5.2 is pure JS thats it one shot. animal edition , i did not even prompt it to be so detailed and it made proper snacks for different animal. for someone who saw my account first time may not how i have access to fable 5.2 just check my previous tweet and also opus 5.2 is…

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.

Claude Fable 5.2 you guys seriously cooked with this model. no assets , no mcp , no inspiration , fully coded in JS nothing else. see my cute claude mascot and this world everyone is drawn in code

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.

fable 5.2 > gpt 6 astra. tested both models with same prompt at high reasoning and results came out really different. fable next model entered stealth testing today, so i don’t think it's coming out anytime soon. from early testing: huge step up from current fable

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.

Anthropic is currently stealth testing Opus 5.5 (`claude-opus-5-5`) under the codename `claude-wafer-eap` which is planned to be released on Tuesday.

Anthropic added "imminent" note and partners only got access for 24h. Dated for Tuesday, actual release could be Monday (!!) as well. Either way, it's the upcoming week. Thinking is ALWAYS adaptive (no "off" mode). Forced tool use is retired.

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.