We've come to learn that, just after a year and a half stay, Clint Hocking and Valve reached a parting of ways. This is according to Clint's personal blog and LinkedIn account.
We never found out, officially, what he was working on while he was there. The bio page on his personal blog says that his specific roles were "designer and level designer" at Valve. And, according to the Jira database leak from last October, he was assigned to the Left 4 Dead 3 project.
Before joining Valve, Clint's more notable role was Creative Director at Ubisoft for nine years, where he worked on Far Cry 2 and the original Splinter Cell. According to his blog, he was also a script writer for Splinter Cell, and he was "honoured for his writing work on the title with the first-ever Game Developer’s Choice Award for Excellence in Scriptwriting."