I remember in the 2010s reading about them and also reading that there are de facto hierarchies within Valve for given projects, even if they aren’t explicitly laid out.
People could self-organize, on-demand, for a task, and structure whatever hierarchy was appropriate, based on somewhat optimal resource allocations for that task.
(Example: Person A might normally be the most experienced at facilitating the group's coordination, but A is providing key technical expertise for this task. Person B isn't critical path on this task, and has facilitating skills and interest in that role, so B volunteers for that role for the duration of the task.)