All the M1 Macs can be upgraded to 16 GB, including the Air, and macOS uses memory compression by default, so there can be a bit more life to these machines than you'd otherwise expect.
Edit: Since posting this comment, the parent has been edited to include "hope you got the 16G version" -- at the time I replied, jacquesm's comment mistakenly asserted an absolute "maximum memory size of 8G."
It's a custom build option, I'm guessing you're onto the page with the couple of preset options? If you click "select" on a model you get a second page that lets you customise stuff like RAM and SSD.
Edit: Since posting this comment, the parent has been edited to include "hope you got the 16G version" -- at the time I replied, jacquesm's comment mistakenly asserted an absolute "maximum memory size of 8G."