To date, the latest forum post is here, but I’m sure that will change in the future.
I believe HAS is turned ON by default, but you can confirm over serial (Receiver/Constellation) :
An updated Postcard will automatically use HAS if no other correction source is available. That assumes you are using an antenna that’s compatible with the E6 band, HAS is turned on, etc.
Most software applications will report RTK Float, after the HAS solution has converged. Convergence takes 10-15 minutes. Generally speaking: you can move around as long as the antenna isn’t obstructed causing a cycle slip.