And while it has flirted with the idea of expanding that limit, it is sticking with the limit for now—and indeed, it uses that limit to the maximum in a "Happy Birthday" message to itself in a new video thanking users for a decade of growth.
The social site embedded the spot within a tweet, of course—which is only natural for a company that aggressively trying to boost its video services. But the 140-character birthday message actually appears only in the video—not as its own tweet.
The tweet itself announces Twitter's intention to celebrate the birthday time zone by time zone, like New Year's Eve, as March 21 progresses.
The video itself is pretty standard fare, crafted very much like typical year-end videos made annually by the likes of Google, YouTube, Facebook and, yes, Twitter—except, of course, it covers 10 years instead of one. But the message is familiar: It thanks Twitter users for connecting on the site every day, for a decade, about the things they care about—from the personal to the political.
And it frames all the events, of course, with the Twitter conversation around them.
"As March 21 begins around the world, each of our global offices will kick off the day by showing our appreciation and gratitude—starting in Sydney and following the sun to headquarters in San Francisco. We are excited to celebrate with all of you," Twitter says in an accompanying blog post.
"Throughout the years, you've made Twitter what it is today and you're shaping what it will be in the future. Thank you for making history, driving change, lifting each other up and laughing together every day."
And it looks like we'll be getting more videos throughout the day celebrating individual users, like this one about @KatyPerry.
The birthday tweet in the video, meanwhile, might seem like it's 142 characters. But in fact, the heart and Twitter symbols at the very end are automatically generated by the #LoveTwitter hashtag if you post through Twitter's official channels and not a third party.