I saw Pi on the front page of Hacker News a few weeks ago, I think.

Anyway, I've been trying it for the past day or so and I must say, this is awesome. The extension functionality in particular is great news at least. But there's a lot more to love that seems to actually have been tastefully crafted by real people; a lot of power-user features that would fly right over most agentic implementers, such as branching on the level of individual tool calls rather than only by user messages as in Claude Code. It feels incredibly good, I am very happy with it.