Based on my conjecture that Anthropic is ahead on AI research, and that OpenAI doesn't know how to make Fable-class models.

I suspect the same just based on their versioning scheme fwiw.

Fable is allegedly a massive model (estimates between 6-10+ trillion, with a few hundred billion active). If 5.6 is just an incremental upgrade over 5.5 (at the same model size) then it won't be able to fully compete with Fable just yet.