Twitter CEO Dick Costolo has announced that the micro-blogging service is now processing half a billion tweets a day. Costolo revealed this at the Internet Advertising Bureau’s Engage conference in London, which is up from 400 million daily tweets that Twitter had publicized in June 2012.

Costolo also confirmed reports that Twitter is testing out “like” and star buttons to potentially replace the “favorite” tool the service has used for years. The company had previously declined to comment on the issue and did not immediately respond to a request for comment on Costolo’s reported remarks in London.