Apple will introduce new versions of iOS and OS X at its annual developer's conference.
Apple Fixes Broken Twitter Links in Safari in Third Beta of OS X 10.11.4
Safari users have used temporary solutions, including reloading the "t.co" link several times, removing "https" from the URL, clearing Safari's cache, or switching to a different browser, but until now there was no official fix yet for the link loading issue. Chrome and Firefox are not affected, nor are links that do not use HTTPS.
Last month, WebKit Developer Experience Manager Timothy Hatcher tweeted that the problem was lower level than WebKit, Safari's underlying rendering engine, and that Apple had a fix identified. OS X 10.11.4 should be released to the public by no later than the end of March, depending on how many beta versions are tested.