It is and has always been open source: https://github.com/bluesky-social
MIT license.
Discussion
The UI was closed source for a long time. Of the 11 repos in that list, I see only 4 as MIT. Bluesky doesnt have a free software mindset, imho. But that's OK, different ways of doing things. I hope they use nostr key pairs and interoperate with nostr via a bridge.
Yep, open source like android, darwin, and webkit are open source. The code is open but the process isn't.
I’m also hopeful about a gateway between nostr and atproto.