When you work at Twitter, you get near-daily updates to the app to test. These beta versions often provide a glimpse of new features, and most of them are small. So when a major update landed two weeks ago, one thing stood out: The quill icon, which everyone knows you press to compose a tweet, was no longer an icon, but a single word: Tweet.

This experiment in iconography didn't last. A subsequent update brought a new tweet button, and another after that. None of them outshone the quill, and so it remains. But starting today, so much about it looks different. It's Twitter's biggest redesign in years.

Twitter, Inc.

Every solid gray icon is now a lighter outline drawing. Headers now appear in bold, to help you navigate more easily. The home icon is still a birdhouse, but it lost the perch---you'll see just one hole instead of two. A little less bird-y, perhaps? Round avatars help distinguish users from tweets. Retweet and Like counters update in real time, letting you watch tweets go viral. And the reply button gave way to a speech bubble that Twitter hopes is clearer in its purpose.

Despite the changes, Twitter still feels like Twitter. And more than any one change, the redesign makes a statement about the platform: The look of the tweet button isn't what makes Twitter, well, Twitter. Neither is the shape of the avatars, the shading of the icons, or even the character count. What makes Twitter is @realdonaldtrump, @dog_rates, and each of the other 328 million or so monthly users who log on each day to answer the platform's perennial question: What's Happening?

Twitter unveiled that tagline a year ago. It's not a question, but a statement. Twitter wants to be the place you go to see what's going on. These sorts of brand exercises mean little to regular people, but in talking to Twitter execs, the changes clearly made an impact internally.

"Nobody knew what Twitter was for," says Keith Coleman, the vp of product. "Or, rather, they knew it was for a thousand things. It was for chatting with people, for sports, for whatever. It's very clear now."

After the rebranding, the product and design teams thought the time was right for a makeover. "I think the design team felt like it was the right moment, because Twitter finally had a clear of what we're doing," says Grace Kim, head of user research and design. Years of surveys and user studies revealed the same thing: Users found Twitter too complicated. The team knew that tweets must be front and center. Everything else was negotiable.