The difference I am pretty certain is the type of capacitors used in the bypass. The poly is the standard, and the Anniversary used to be Jupiter Type 2 but now I believe that Steve is using Miflex copper capacitors for the upgraded bypass.

There is a significant sonic difference I believe. (Though I have had the poly caps and the Miflex caps both in separate components, I have had the Mifle in a bypass in the ZROCK2 and the poly in a non-bypass ZROCK2. I would describe the Anniversary with Miflex as more revealing of detail and dynamics--noticeably, more than a subtle difference.

But there's this: you'll hear more of everything with the Anniversary, which means you'll hear shortcomings of source and cabling etc. In my case that led me over time to upgrade, upgrade, upgrade. . . and at times to be more about the gear than the music. I've come across to the other side of that now with all my components with great sources and upgraded caps but one (ZTPRE) and very happy . . . but it was a journey of time and money. But that may be just me. I've been susceptible to that on my audio journey, not everyone is.

So for me it's a worhtwhile upgrade, but I can also understand choosing the poly upgrade and being very happy without embarking on a longer audio trek.

Hope this makes sense and helps.

Thank you for the quick responses. I will call and add the mod on Monday
As far as  my other equipment, I  have
vpi prime tt, ps audio stellar phono pre, don sachs linestage, bel canto e one streamer , and spatial audio x5 open baffle speakers.  I think my gear is up to snuff at this point and do not expect the anniversary mod to cause any upgraditis ( at least for the near future )

Steve noted in the description of the type 2 that the Anniversary mod was now standard.

Not sure if this link/thread helps.  Unless I misunderstood, it comes with the anniversary mods....
Bob
https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1608681355

Good find.  That clears up a lot.