This was my experience too. I asked fable to implement a (quite complex, novel) CRDT engine. It did fantastic work for the 3 days I had access to it. The spec it wrote is exactly what I want. It used prototypes and examples to figure out some hard problems and answer a lot of complex design questions. Claude Opus has been lumbering along over the last week trying to turn what it did into a useful library. As far as I can tell, by trying to vibe together pieces of work fable did without understanding it properly. Opus makes mistakes constantly, misunderstands the spec, and it makes terrible engineering decisions. Earlier today it claimed it proved something was impossible. I asked it to think that through and it immediately backtracked and apologized. Was it right then, or is it right now? Claude has no clue.
I'm kicking myself for not using Fable more while I had it. Now that I've used fable, I'm not sure I even want opus any more. It might be more efficient in the medium term to just program everything myself until I have access to a similarly capable model.
I feel like Deepseek, opus, etc are only good at problems that have already been solved 100 times on github. They're like the iPhone 3G. Its exciting they exist at all. But subsequent versions make them seem like cheap junk.
I had a similar experience. For complex maths in my 3d engine around IK, made more progress in those 3 days than I would’ve done in weeks.
I recently discovered though that ChatGPT 5.5 Pro is almost as smart but only available to me via the ChatGPT app. I’ve been having it read my code and having Opus 4.8 use the ChatGPT app to collaborate. It’s a step down but its a temporary stopgap for complex problems.
It's been pretty cool (and a bit scary) to hear similar experiences from many other researchers and developers just how impressive Fable was for their particular workflow and the productivity it seemed to unlock. Personally, I have found that I can't let any of the other AI agents touch the code that Fable produced for me, since they consistently fail to understand the very delicate choices that it made to ensure optimal performance.
I'm kicking myself for not using Fable more while I had it. Now that I've used fable, I'm not sure I even want opus any more. It might be more efficient in the medium term to just program everything myself until I have access to a similarly capable model.
I feel like Deepseek, opus, etc are only good at problems that have already been solved 100 times on github. They're like the iPhone 3G. Its exciting they exist at all. But subsequent versions make them seem like cheap junk.