Naturally, the company announced the changes via tweet (and jazzy video) overnight:
Say more about what's happening! Rolling out now: photos, videos, GIFs, polls, and Quote Tweets no longer count toward your 140 characters. pic.twitter.com/I9pUC0NdZC— Twitter (@Twitter) September 19, 2016
Here's what you need to know.
What is included in the new rules?
Previously, a picture, video or a quoted tweet used up 23 characters - but that's no longer the case.
Now posting a gif, photo, video, poll or another person's tweet won't take up any characters at all.
It's a step forward from a previous change, in which links were universally shortened to 23 characters - but continued to encroach on our precious 140 character limit.
What isn't included
Alas, links will still take up characters.
Twitter has also previously said it's planning to change @ replies (when one user addresses another) so they no longer have to put full stops if they want the whole world to see it - although that doesn't appear to have been rolled out.
"New Tweets that begin with a username will reach all your followers. (That means you’ll no longer have to use the ”.@” convention, which people currently use to broadcast Tweets broadly.)," it said back in March.
"If you want a reply to be seen by all your followers, you will be able to retweet it to signal that you intend for it to be viewed more broadly."
And that rumoured 10,000 character limit doesn't appear to be any closer to manifesting itself. Which is a relief - we worked out what 10,000 characters looks like using the opening chapters of several of the world's most famous books. It's pretty long.