Twitter posts have been limited to 140 characters, give or take with some quirky rules, for some time now. However, new rules allow Twitter users to post video, photos, polls, gifs, and quoted tweets without using up any of their allotted 140 characters.
Previously, each additional item or feature was counted as 23 characters. The changes are largely seen as an acknowledgement of the increased sharing of multimedia elements. Now there is more room to post the items that gain the greatest engagement.
This change allows more room to post commentary on each post. Previously Twitter users who wanted to say more than a few words along with a one of these items would have to post a screenshot image of a longer message. Or, the could post multiple tweets in a row, replying to themselves, known as a tweetstorm.