My friend's main study that he cites is https://www.sciencedirect.com/science/article/pii/S209525462... . The interesting thing is that there is no real cutoff. The benefit kind of tapers off logarithmically, but all-cause mortality just gets lower and lower the more steps/day you take. So his 12k is somewhat arbitrary.

> Also, I've found that suggesting 30 minutes of walking vs ??? minutes of walking to get 10k steps is easier for most people to fold into their schedule

And 10K steps is a good bit more walking than 30 minutes. IMO the 10K number might be halfway useful as a high level metric for people who are just judging their own activity throughout a day. As you've pointed out, if you are going for a brisk walk, you don't need 10K steps to get value from it.

I also like the Japanese Walking's focus on time versus number of steps because I can go for a walk with my parents and all three of our phones calculate different numbers that directly correlate with our gait. Mine is often half of theirs.