just found his old message on instagram - should have looked there first. Here is his reply.
Hi Adam, it is made from 440-c, guard is 440-c as well.
Hope this helps.
From 2008 I heat treated all the hollow handles in a way that the joint is much tougher, the shaft which goes inside the handle as well as the recasso area
Was heat treated tougher.
If you purchased your knife before 2008, all the blade is one hardness, I believe if I can remember they were heat treated around 57-59.
eta for clarification - knife was purchased before 2008.