Twitter's 140-character limit is already rather, well, limited. It's been one of the cornerstones of the product and it helped create the tone and identity of the site, but there are plenty of times when you wished you had just a couple more characters.
Don't get your hopes up though, tweets are getting even shorter if you decide to include a link. Starting next year, short links will take up 22 characters instead of 20 for plain HTTP links and 23 instead of 21 for HTTPS ones.
These changes affect users, who will have to cut their tweets even shorter, but even more so developers who may need to update their apps to take this change into account.
There's no explanation for the change, t.co short links have eight characters for the codes, so there are hundreds of trillions of possible combinations, more than enough.