I've been at three FAANGs now and my experience has been that nobody really cares about your level for day-to-day work. The only times it has ever come up for me is when a) I was part of assembling a new team and we needed a mix of juniors and seniors or b) when some dangerous action like deploying during a holiday code freeze needed approval from an L9+ by policy, so you had to go find that person and justify it to them.

Now, your compensation is based entirely on your level, which obviously makes it matter a great deal, but my experience hasn't been that there are mind games around it.