Threads doesn't initially support ActivityPub open standard, and is not open source. Adding ActivityPub support doesn't preclude withdrawal later.
> Will Meta embrace-extend-extinguish the ActivityPub protocol?
> There are comparisons to be made between Meta adopting ActivityPub for its new social media platform and Meta adopting XMPP for its Messenger service a decade ago. There was a time when users of Facebook and users of Google Talk were able to chat with each other and with people from self-hosted XMPP servers, before each platform was locked down into the silos we know today. What would stop that from repeating? Well, even if Threads abandoned ActivityPub down the line, where we would end up is exactly where we are now. XMPP did not exist on its own outside of nerd circles, while ActivityPub enjoys the support and brand recognition of Mastodon.
https://blog.joinmastodon.org/2023/07/what-to-know-about-threads/
@daviding
Without looking, I'll guess that they never quite did. :)
For those who think that open standards can be easily added on after code had already shipped, there's an extensive case study on Microsoft Office and OOXML. Here's a fun question: how long did it take Microsoft to meet the specification that they themselves wrote?
http://openinnovationlearning.com/online/