I just sold a gun and acquired a new 4" Max 9 in the deal. I went on Ruger's site to look up specs, and it is not listed. Did Ruger drop this model already?
Where are you seeing a "pro" model ....?The Max-9 with the 4" barrel is not a separate model. It's simply the Max-9 "Pro" model that comes from the factory with the extended/threaded barrel installed. The "Pro" denotes it comes with no manual safety and, crucially, that longer barrel. The standard Max-9 has a 3.2" barrel.
So, if you go on Ruger's site and look at the Max-9 Pro, the listed specs will show the overall length, and if you look closely at the pictures or description, you'll see it's the 4" threaded version.