I am quite impressed with Fable 5. I used the £18 subscription, and asked it to convert the document processing of Practal Zero [1] from running in the same thread as the UI to a worker thread. Just two days before I gave the same task to Codex, and the result was not really nice: it would copy the entire document to the worker thread as a snapshot for processing, and so on. Fable instead realised that it could make use of the fact that I have a self-made custom database based on operational transform running (that's why document loading is so slow :-)), and made the document processing to be just another client of that database. It discovered even a bug in how I sync between the "livemodel" (in-memory replica of database state) and ProseMirror's model. That sync made problems before, and I had written a spec up for that, convinced that my "fourth attempt" at it would be correct. Fable found a last bug in the spec, corrected it via a "fifth attempt", and fixed the corresponding code.

The reported API costs for all of that would have been $180 though, which I cannot afford when the Fable promo ends on June 22nd. I am also a happy user of £89 Codex, it is really reliable and works very well, but Fable seems to be just noticeably smarter.

[1] https://zero.practal.com

Umm? I'm getting usage capped on single prompts of Fable 5 with the $20 subscription.