just from the quickest skim of opencode (havent tried it) I'd say the difference is pi.dev is barebones and you can add extensions as you please, I saw this in the opencode readme:
>OpenCode includes two built-in agents you can switch between with the Tab key.
so it sounds like it's just more opinionated on what works well, maybe I'll try it sometime since I sort of fell into that pattern in the past: discussion and writing a SPEC.md and then passing it off for implementation
