We started experimenting with this on a large-ish feature, with several repos involved. Off to a good start. The constitution that’s created as the first step is valuable in its own right. Something that can be used for onboarding both engineers and LLMs. Version 1 generated by specify was already quite good and we iterated from there. We had previously created a Claude.md that took the whole codebase into account, which I think helped.
I’m perhaps less sold on the idea of the spec being the source of truth — would have to do some design iterations and see if that holds up. I do like that it imposes some structure/rigor on the design process.