There may be some additional westbound traffic on Highway 520 this evening.

Facebook's hosting a special recruiting event at its Seattle office, which has bulked up with former Microsoft and Google engineers since it opened near Pike Place Market last year.

The company had scheduled a tech talk for tonight with its vice president of engineering, Mike Schroepfer, but that's changed.

Now the event has morphed into a recruiting event and the featured guest is Chief Executive Mark Zuckerberg, who will meet with potential recruits starting at 7. A spokesman said Zuckerberg visits the office periodically.

Xconomy noted that all of the free tickets for tonight's event were gone in 20 minutes.

Facebook's Seattle office currently has six engineering positions open and a spot for a technical recruiter, but the listings aren't definitive.

I wonder if Zuckerberg will also visit his pal Bill Gates while he's in town.

Facebook's among a series of California tech companies that opened Seattle offices over the last year to tap the area's talent pool. That contributed to Microsoft's decision in April to increase its pay in what Chief Executive Steve Ballmer called "the most significant investment in overall compensation we have ever made."

UPDATE: Facebook will webcast Zuckerberg's Seattle session here, at Facebook Live.

UPDATE 2: Facebook decided at the last minute not to webcast the event after all.

Mark Zuckerberg spent a bit of time with reporters before the event began, describing progress at the Seattle office.

"The office is going really well," he said.

Rather than focus on a particular project, it's integrated with the broader development work at the Palo Alto headquarters.

"Now we're starting to get to the scale where we're attracting a lot of really good people and we're starting to lead a bunch of projects from out here," he said. "Most notably there's a lot of mobile development."

Zuckerberg declined to project how much the Seattle office will grow. Currently it has about 40 employees in an office tower at First Avenue and Stewart Street.