Not sure if you've seen their handbook? Search for "valve handbook" - it's an internal thing, but someone leaked it a few years ago and now it can be easily found, it explains their culture very well.

The Valve handbook doesn’t reflect the reality at Valve. Not all employees have the power to fire other employees or decide the salary of other employees. The employees that do have all the power and the rest compete with each other to build beneficial buddy relationships with them.