Earlier today, Twitter
announced (in a tweet) that it has filed with the US Securities and Exchange Commission (SEC) to go public. Companies with less than $1 billion in revenue per year can file for a "secret" initial public offering, which prevents public release of documentation associated with the filing, such as assets, and revenue estimates.
Little information is actually known about the filing. The "secret" status obviously makes the company's earnings less than $1 billion annually, but a timetable, number of shares, and other pertinent facts are likely to not be made public by the company during the IPO process.