If you compare the numbers of common stock issued
Post# of 22940
That is a retirement of 1,465,313,497 shares of common stock.
This verifies the FORM 8-A released on Feb 10, 2016 which stated "As of the date of this Form 8-A, there are 2,944,402,694 shares of our common stock issued and outstanding.
I don't believe there have been any other statements by Bill, tweeted or otherwise, since the Form 8-A about further share retirement. So, it's 2.9 billion issued and outstanding. However, nothing would prevent him from reducing the share structure further, as he has indicated that he would like to do.