No, they are not sweat resistant.
Sony does NOT cover damage caused by perspiration in their Limited Warranty.
(found under https://www.sony.com/electronics/support/wireless-headphones-bluetooth-headphones/wh-1000xm4#manuals)
Under Sony's warranty it says:
"This Limited Warranty does not cover products purchased from sources other than Sony or a Sony authorized dealer (including non-authorized online auctions), or issues due to:... (vii) contact with liquid, heat, humidity or perspiration, sand, smoke, or foreign materials"
With that said, there are people that have no issues with sweat (even excessive sweat) while wearing them. So it's up to your discretion. But just be aware that Sony has covered their behinds if something goes wrong with your headphones since their exclusion of coverage is in writing. They won't replace it or service it for you for free.