L3 is new grad. L4 is "terminal" in that there's no explicit up-or-out pressure beyond that point. L5 is senior, and I'd say most people don't make it beyond L5

L3 is new grad. L4 is "terminal" in that there's no explicit up-or-out pressure beyond that point. L5 is senior, and I'd say most people don't make it beyond L5 without intent. L6 has a few shifts from prior levels. Notably that a high performing L3 is an L4 and a high performing L4 is an L5 (usually), but simply performing well at L5 isn't enough to get to L6, the scope of work and goals shift between L5/6. You generally won't be considered for L5 without 10+ yoe, as I understand it, although internally you can reach it faster.