Right mac for the job?

For context, I'm a software engineer looking to buy my first apple silicon macbook(air). Over the last couple of days I've been doing some research on the m4 air 512G and had determined that was the best option for me at the moment. However when I went to place an order on Amazon, I found there are m5 airs that are listed at a cheaper price than the m4 air which prompted this question. Why are they cheaper and what's the better mac to buy.

also the built for AI tagline