Original story: Star Filled Studios is a two-man outfit, founded by ex-Popcap and Blizzard guys Tod Semple and Jeff Gates, who both worked on Plants vs. Zombies and Diablo 3. "We are opening a new Valve office on the San Francisco peninsula," Semple's LinkedIn profile reads, revealing Valve's acquisition took place in November.
Semple doesn't say anything in regards to what Valve plans to do with this satellite offices in San Francisco, though current speculation is that this move mirrors Valve's acquisition of Turtle Rock Studios in 2008, buying the developer and then finishing Left 4 Dead development on its own. Star Filled has not announced any projects of its own, so it is uncertain what the studio was working on previous to acquisition.
Semple's blog talks about going up to Seattle to visit Valve in September, so we can only imagine this is another Turtle Rock scenario. Again, that's only speculation at this point – we've inquired with Valve for more information and will update accordingly.
[Thanks, FHorrigan; image credit]