"terminal level", in the sense being used by the OP, doesn't mean "end of the IC track". It means a level that you can be at "forever". Often times the junior engineering levels have some expectations around eventually being promoted (ie, "up or out").

IIRC, at Google the levels below Senior Engineer require progress toward a higher level as a job requirement. So that even if you're performing well at that level, if you aren't showing progress it gets counted against you in perf increasingly until eventually you are at risk of being pushed out.

Correct, this is what I meant.

Terminal level and Max mean different things here.

Indeed you can become a senior fellow at Google, but you aren't expected to. You are however expected to hit senior at some point in your career. There's no requirement to grow further, so the bar for senior is high.

I think google itself follows that same path of promotion, ending in a fellow position after distinguished engineer? I wonder how many people at google have the fellow title.

It doesn't sound like they meant that senior was the last possible level, just the last level to which promotion in a career should be expected through "normal" growth and development. It looks like less than 1-2% of engineers at my company (FAANG) are above "Senior".

yeah, but responsibilities (and technical complexity) grows with each step, and many people, for whatever reason, stall out at one level for most of their career.