Beginning October 1st, all t.co links will begin using the HTTPS protocol. Today, we advise partners to reserve up to 23 characters for links in Tweets however non-secure HTTP links only take up 22 characters.
If you’re already using HTTPS in your links or if you already follow recommended practices and reserving 23 characters for links, this change will have no impact on you. If you are using non-secure HTTP links in your Tweets, please be advised that they will now be converted to HTTPS t.co links and they will now take up the full 23 characters possible for a link in a Tweet.
For more information, please see the public announcement of this change: