Cloudflare OS uses pi-agent-core, but not pi-coding-agent. pi-agent-core, at least the way CFOS uses it right now, is more of an LLM API compatibility layer than a full harness. All the tools and things like compaction are implemented by CFOS itself.
The code was actually using ai-sdk (from Vercel) up until a few days ago, when I switched it over to pi-agent-core.
Why doesn't it use Think? Mostly because Think actually didn't exist yet when I started writing this, and the designs diverged in a way that made retrofitting hard. The CFOS harness does a few unusual things, like tracking the entire state of the filesystem as the conversation progresses using Yjs (a CRDT), so we can actually rewind the state to see what the agent saw at any particular point in time.
I would actually like to delegate more to Pi, because I don't think CFOS should be in the business of thinking about how to implement compaction or to optimize editor tools for each agent. But I'm not really sure if it'll be possible without giving up some cool things about the CFOS harness, so we'll see.