The GUI isn't but the underlying pear stack or holepunch/hypercore protocol is.
Discussion
Neither desktop nor mobile apps are open source. We have no idea what is happening. It's just trust us.
The entire pear stack that makes Keet work is open
Pears.com
That's really really cool because other devs can build on that stack, but if the keet app is not open source, it could as well be spyware because we can't verify if it does what it says it does.
It will be eventually. They don't want to give away everything they are working on until it's all working. The behavior of the app makes it pretty clear that it's p2p. Telegram is spyware, Keet is fine.
Yes, holesail/liveport are built on Pear & Peardrive is also being built on Pear. Holesail is already usable.
They've been saying "open source soon" for two years now. My privacy sensitive friends won't touch it until they can verify, and I can see why. Open source is prerequisite for Don't trust, verify.
Don't get me wrong, I'm really grateful that they're building cool shit. It's coming more from a point of: what's actually verifiably secure and private that we can use to communicate?
They opened the underlying stuff. Your privacy sensitive friends still using Twitter & Telegram? Using something doesn't require posting anything especially sensitive in the app. But it's a way to create groups that can't be censored, & we have seen that Telegram can be.
No they're using XMPP only.