It depends. Lots of towns adopt a comp plan that seeks to change lots of the ag zones into SFR, industrial, or commercial over time. So they’ll rezone the properties to have them change when they sell.

In my last city, we’d actually make development agreements with ag owners to annex into the city in return for getting access to water, sewer, and police. We’d agree to exempt them from city taxes so long as they didn’t change land configuration or use, but once they did the new zoning would kick in and everything would have to come into code.