Note: it does seem at least some development happens in the open https://github.com/warpdotdev/Warp

> We are planning to first open-source our Rust UI framework, and then parts and potentially all of our client codebase. The server portion of Warp will remain closed-source for now.

https://github.com/warpdotdev/Warp/discussions/400

None of the server bits will be open, ever, but some of the UI code will be? Better than nothing.