Sergey Brin and Larry Page Wendel Fisher/Flickr, Ralph Orlowski/Getty Images Google cofounders Larry Page and Sergey Brin are going to sell about $4.4 billion worth of company shares, according to a new filing with the SEC (which we first spotted thanks to Footnoted).

It's basically an extension of a plan that was previously in place but expired at the end of January.

As of January 30, 2015, Brin and Page held approximately 44.6 million shares of Google Class B stock and another 44.6 million shares of Class C stock.

Under the new trading plan just filed, they will sell approximately 2 million shares each of Class B common stock (which will automatically convert to Class A shares upon sales), as well as another 2 million shares each of their Class C non-voting stock.

After the transactions are complete, they will collectively own about 40.6 million shares of Class B stock and another 40.6 million shares of Class C stock, the filing says.

With both classes of Google stock trading at approximately $550 a share, the total 8 million shares they plan to sell translates to roughly $4.4 billion. The filing didn't specify when exactly the sale will take place, but it will be extended over a period of time to minimize market impact, the filing said.

Even after Page and Brin sell $4.4 billion worth of shares, they'll retain majority control of Google. Following the sales, Brin and Page will own only 11.9% of Google's outstanding Class A and Class B common stock, yet still hold 52% of the voting power.

This is possible because of Google's dual-class share structure. Class B shares, mostly owned by Brin, Page, and Google Chairman Eric Schmidt, hold 10X the voting power of the common Class A stock. It's why Class B shares are often called "Super-voting" shares. (The Class C stock, introduced in 2012, has no voting power at all. Here's an explainer if you're confused as to why Google would do this.)

Google founders Larry Page (L) Sergey Brin talk with members of the media at Google Press Day 2006 May 10, 2006 in Mountain View, California Getty/Justin Sullivan Dual-class structure is now pretty common among tech companies, as Facebook, Linkedin, and Box all have adopted this model. But Google was one of the first companies to bring this to the mainstream when it went public in 2004.

It was very rare to see investors allow this type of structure because it gives too much control to insiders when a company is supposed to be publicly owned. Prior to Google, it was mostly family-run media companies, like The Wall Street Journal and The New York Times, that had this model, all under the name of protecting editorial independence.

Google duly acknowledged this in its S1 back in 2004, as it wrote, “We are creating a corporate structure that is designed for stability over long time horizons...By investing in Google, you are placing an unusual long term bet on the team, especially Sergey and me, and on our innovative approach.”