Twitter today announced via tweet that they're filing paperwork for an Initial Public Offering. Specifically they say they've "confidentially submitted an S-1 to the SEC for a planned IPO.."
That appears to mean that they're taking advantage of one of several deregulatory provisions of the laughably named JOBS (Jumpstart Our Business Startups) Act which allows firms with less than $1 billion in revenue to go public with a substantially reduced amount of public disclosure. This was done supposedly in response to the fact that smaller firms were becoming too reluctant to go public. Why that was a problem, exactly, I couldn't quite say. Or rather it was clearly a problem for Silicon Valley founders and venture capitalists but not obviously a problem for the public interest.