Chain every 2-3K, cassette about every 4 chains. How long the chain lasts depends on how much off-road, and how often I get around to cleaning the drivetrain...

Then there are the many parts I swap out to make the bike more comfortable over time like bars, bar tape, grips, pedals.... Or perform better like bigger cassette, different shifters. Seems I can't leave well enough alone. I am always changing /upgrading something.