Lots of misinformation here about regens.
First, yes, the new diesels do still regen, and yes the DO use diesel fuel to regen.
Second, DEF is used to lower NOx emissions in order to meet emissions regulations. All trucks with DEF us a special DEF injector to inject DEF into the exhaust to mix with the NOx. The chemical reaction breaks down causes the NOx to combine with the NH4 in the DEF to produce water vapor.
Thirdly, DEF itself does not affect regens and in no way is it tied to regens. However, the use of DEF to reduce NOx allows the trucks to run less EGR, thereby running a bit higher combustion temperature, resulting in less soot buildup in the DPF, which in turn requires less regens. More infrequent regens leads to better fuel economy. Make sense?
They may not be 100% correct, but it is a lot closer than some of the other posts.