Previous hybrid shafts have been interchangeable when the models changed. I would imagine that this will hold true for the 818s. I have two 816h1 and neither have the same shaft. One has the Aldila Black Rogue and the other has a Fujikura Tour Speeder 8.8. The Black Rogue is a later model 17* head and the speeder shaft did not perform as well with that head at the fitting. I would suggest going to a fitting at a range, if possible, and see how your current shafts perform in the new hybrids.

Not official, but 913/915/816 are interchangeable and the 816 and 818 will likely share the 1 degree loft adjustments.

@Chuck Z; Interesting point. I can hit my 23* 816 really well w/ Tour AD DI 85R shaft. I struggle hitting the 19* and for some reason I always have. I am at the point of wondering if I need the 19* at all but its too much gapping between my 15* fw wood and hybrid.

I have a similar question but going from 915 to the 818. I have played the 915 H (21* and 19*) for the past 3 years and am thinking of upgrading to the 818 H2. I love the Fujikura Motore Speeder HB 8.8 Tour Spec shaft in my 915's and would like to be able to put them in the 818's. Is that possible?