"Tags work a little differently than hashtags do on platforms like Instagram and X (formerly Twitter). When composing a Threads post, you start a tag by tapping the # symbol and then typing out your topic. But instead of being limited to just one word, you can type out a whole phrase (with spaces!) and add special characters, according to Mosseri. However, you can only make one tag per post."

I wonder how the tags will work if they federate with ActivityPub.