My own experience: much less context bloat, and hidden system prompts. Can tune it to your own workflow, instead of dealing with whatever hidden system prompt Claude Code forces on you.
I didnt personally used OpenCode for heavily, but i remember when i ran it on the server it's TUI was more expencive to run, comparing to PI, so it lagged af. Meanwhile PI doing the same (or even better) job, has very minimalistic and fast TUI, it is like as minimal as possible agent CLI tool.