Facebook’s plan to let employees sell vested shares at a $4 billion valuation to outside investors is going into effect November 1, Valleywag reports. According to the rumors, the company has a right of first refusal over any employee stock sales, which could effectively make the sales a buyback operation.

Facebook’s program will let shareholders sell at $8.90 a share, which represents a company valuation of $4 billion; some buyers are offering $11 a share. If too many transactions go through at the higher price, Facebook may have to revalue its shares, which will have untoward tax implications for the company and other employees.

It’s not clear what Facebook can do, short of rewriting its corporate bylaws. But the formal program does have one thing going for it: It will be formal, organized, and predictable. For geeks who’d rather optimize code than their own financial returns, letting their managers handle their money may seem easier.

Exactly how much stock Facebook employees will be allowed to sell, however, is rumored to be the lesser of 20% of their holdings or $900k. That’s enough for a good down payment on a 3 bedroom near the company’s downtown Palo Alto offices.