The right number of levels for OKRs
Ultimately OKRs should comprise three levels: objectives, key results and initiatives.
However, how you structure this hierarchy across your organisation depends on your size. For example, do you want to set objectives at the company level or department level? Does each micro-team within a department get team-specific key results, or do they get initiatives? Should each team member have their own initiative, or is that set at the team level?
To make OKR setting within the 3-level structure simpler, check out this OKR Quickstarter e-book.