Back in May, Twitter revealed they were changing the way their tweet character limit worked. Currently everything you can shove in a tweet - text, media, polls, etc - counts towards the 140-character limit. Twitter has not revealed the exact date this change is coming, but The Verge believes it will be September 19.
The change will go into effect for images, GIFs, polls, and videos, although The Verge is unsure if it will all happen at once or over a gradual period. However, they are confident that it will start on September 19. In replies, the original user's @username will no longer count towards the 140-characters either. It appears as though links will still affect the character count, but with Twitter shortening all links regardless, this is less of an issue.
Twitter's character limit is a holdover from a simpler time, when Twitter was mostly used over SMS. However, most users (including myself) would argue that the character limit is what distinguishes Twitter from other social networks. Information has to be compressed into a 140-character blurb, instead of a long-winded essay that you might find on Facebook or Google Plus. Though, part of me wonders if this will lead to the character limit being expanded in the future.
- The Verge