It is unclear whether Valve are setting up a San Francisco office or not, or whether this classes as an acquisition or a hiring.
Valve has acquired an indie studio set up by a former Diablo 3 and Plants vs. Zombies developer according to one of the startup's founders.
Star Filled Studios was established only a few months ago in September by former Blizzard North, PopCap and LucasArts developer Tod Semple and former PopcCap, Blizzard and Maxis developer Jeff Gates.
Semple revealed that the studio had been acquired by Valve on his LinkedIn profile. He and Gates both also changed their job titles to 'developer at Valve Corporation'. Semple also states that Valve will be opening up a San Francisco office.
Semple is listed as having worked on Diablo 3, Star Wars: The Force Unleashed and Plants vs. Zombies whilst Gates is listed as having worked on Darkspore and Spore.
Valve vice-president of marketing Doug Lombardi however told Joystiq that it was 'better categorized as Valve hiring two new employees instead of an acquisition of a company.'
He also stated that Valve is not necessarily opening up a San Francisco office, despite Semple's comments.
Although Valve is known to look for and bring in fresh talent on a regular basis, it is not known for acquiring other studios. The only other acquisition of note that it has made in its history was Turtle Rock Studios in 2008, which was responsible for the initial development on Left 4 Dead.
The new employee handbook issued by Valve to its new starters leaked onto the internet earlier this year and reveals just how much leeway the developer gives its staff when it comes to working on specific projects. Examples from the handbook include the fact that employees are not assigned managers and their desks are fitted with wheels to make it easier to move around the offices to work on different projects.