Twitter uses different fonts for its various versions and devices. Here are the fonts used by Twitter according to the search results:

• Twitter web on smartphones and tablets: Helvetica Neue
• Twitter on Windows: Arial and Segoe UI
• Twitter posts: Open Sans, Helvetica Neue, Arial, SF Pro, and Roboto
• Twitter logo and branding: "TwitterFont," a unique font created especially for the firm, which is a sans-serif typeface with rounded edges

Twitter has changed its font several times over the years. In January 2021, Twitter launched its first-ever custom typeface called "Chirp," which is used in both the web and app versions. Before Chirp, Twitter used fonts ranging from SF Pro, Roboto, and Helvetica Neue, depending on the OS and device.

It is worth noting that the font size and family used by Twitter as its default may vary depending on the device and version. For example, Twitters Mac version adopts the Helvetica Neue font, while the Android app uses Roboto Font, and the iOS app uses San Francisco font.