Erik Wolpaw, a long-time Valve writer who has worked on game series including Half-Life 2, Left 4 Dead, and Portal, revealed today that he is no longer with the company. Marc Laidlaw, himself a former Valve writer, let the news slip on Twitter, while Wolpaw confirmed it in a status update on his Facebook page.
Wolpaw joined Valve in 2004, and has credits on Half-Life: Episode One and Two, Left 4 Dead, Portal, and Portal 2. Prior to that, he was with Double-Fine, where he co-wrote the outstanding platform-adventure Psychonauts, and before that he was one-half of the brilliant (and sadly defunct) gaming site Old Man Murray. He's currently involved in the development of Psychonauts 2, which was successfully crowdfunded in early 2016.
A reason for Wolpaw's departure wasn't given, but it does appear to be legitimate this time around. A report that he had left Valve also surfaced last summer, but in that case it turned out that he'd just called in sick for the day.
I've emailed Valve for more information, and will update if and when I received a reply.
Update: The report originally stated that writer Jay Pinkterton had also left the company, but apparently not.