The will-they-won’t-they of Threads direct messages has been going on for a while now. Last we heard, Instagram (and Threads) head Adam Mosseri said that Threads was not planning to build DMs. That still appears to be true — but it’s not the whole story.

Mosseri said on Tuesday, in a Threads post replying to Platformer’s Casey Newton, that his reluctance to build DMs into Threads stems from the fact that he thinks Instagram’s messaging service might be the right one for Threads. Threads is, after all, build on top of the Instagram app and is already connected to Instagram in a number of ways. And Mosseri has been hinting for months that he thinks Instagram DMs can be the main place for private chat.

“My hope is that we can make the Instagram inbox work” inside Threads, Mosseri wrote, “and there’s still a lot to do there.” You can imagine what that might look like: you’d be able to message anyone on either platform (which makes sense, given that your Threads and Instagram accounts are so connected anyway), and your inbox would sync between the two apps. Instagram and Threads already have so much infrastructure in common that making messaging work wouldn’t be all that complicated. You can already share a Threads post via Instagram DMs without ever leaving the Threads app, which is a confusing sentence but also a pretty good example of how cross-app messaging and sharing can work.

Mosseri did point out some tricky consequences of this decision, though; notifications first among them. If you have one inbox in two apps, which app should ping you when you get a new message? Surely not both. (If you’ve ever had multiple email apps running simultaneously, you know how annoying this can be.) A cross-platform messaging system also requires a cross-app set of controls and filters, which could get complex quickly.

There’s also the bigger-picture question of what borrowing Instagram’s inbox might mean for Threads’ plan to support ActivityPub and integrate with apps like Mastodon. A version of Threads with federated posts and centralized messages would seem to violate the spirit of the ActivityPub project and also just might not make sense. Meta is also in the middle of preparing for a future in which all its messaging apps have to be interoperable, and CEO Mark Zuckerberg has said that “people should be able to use any of our apps to reach their friends.” That push could change the way WhatsApp, Messenger, Instagram, and Threads interact in even more fundamental ways.

If Threads can’t figure out how to make the Instagram-based strategy work, Mosseri said, the team has two options. It can mirror the inbox anyway and make users solve the notification issues themselves, or it can build “a totally separate Threads inbox and dealing with the fact that you’ll have two redundant message threads with each of your friends with the same handles in two different apps.” Mosseri said neither option seems appealing, but he seems far more against the idea of building an entirely new messaging system into Threads.

At this point, we can almost certainly say that some kind of private messaging will come to Threads at some point. It’s a feature users want, it’s an obviously useful addition to public posting, and it’s just probably going to happen. When it’ll happen and what it’ll look like are still hard to say. It doesn’t sound like Mosseri himself knows. But it sounds like everyone’s best guess is that it’s going to look like Instagram.