Update:

Valve boss Gabe Newell has told Engadget that although the company doesn't usually talk about matters regarding personnel, the "unusual" amount of speculation around this morning's news prompted him to addressing them.

"No, we aren't canceling any projects," he said.

"No, we aren't changing any priorities or projects we've been discussing. No, this isn't about Steam or Linux or hardware or [insert game name here]. We're not going to discuss why anyone in particular is or isn't working here."

Original story:

A number of staff have exited Valve including director of business Jason Holtman, who had been with the company since 2005.

Although up to 25 staff are thought to have been laid off, Develop is reporting that the reasons for Holtman’s exit are unclear.

Those who have lost their jobs include a number of Half-Life 2 designers, along with staff from Valve’s Android and hardware development departments.

Gamasutra heard from some of the affected employees, who described the incident as a "great cleansing".

Firings from the Steam developer are rare, as an employee told PC Gamer last year.

“If it turns out that we made a bad hiring decision, or that somebody is just not working out, there’s a method we use to get the people who are involved in the same room and to walk through the decision about what should really happen as a result of this person not functioning very well,” they said.

“Some of the details are kind of boring, but the main answer is that it’s peer-driven, just like we evaluate each other as peers.”