TWITTER HAS FILED FOR ITS IPO

Twitter has filed for an IPO, it announced on its own Twitter feed. This story is developing. Refresh this page or click here for updates.

Here's the tweet:

In what appears to be a sracastic joke, Twitter immediately followed its announcement with this tweet:

The IPO filing had been expected. Twitter has clearly grown into a huge business - it's expected to do more than $500 million revenues this year and has taken more than $1 billion in funds from investors - and the rumors and chatter swirling around the company had reached a sort of fever pitch.

We noted earlier today that Wall Street and other observers all seemed to be behaving as if an IPO was expected.

The most recent tantalizing clue was the fact that Twitter CEO Dick Costolo declined to answer questions yesterday after giving a speech on leadership at Techcrunch Disrupt.