ARM is cheaper on AWS per the unit of work done, in the general case. But there should be no assumption that ARM is that snappy little brother that will launch your lambdas in no time while x86 is still starting up, this is the kind of idea that I get when reading the comments mentioning ARM. It won’t launch your virtualized environment that noticeably faster. It’ll just do more work for less money, and 40% is probably not the figure that you’ll see in real life.