That's in testing though. Arch has 5.3.0 in core already. Not sure where the .1 comes from since it's not even released yet according to https://gcc.gnu.org/releases.html
Edit: Actually it looks like the versions are just named differently. Debian uses SVN version from 20151205, while Arch uses 20160209. So Arch is more fresh (by 2 months), but uses different naming convention.
Edit: Actually it looks like the versions are just named differently. Debian uses SVN version from 20151205, while Arch uses 20160209. So Arch is more fresh (by 2 months), but uses different naming convention.