I just purchased "The Elder Scrolls V: Skyrim Special Edition"

The version that was installed is 1.6.659.0.8. I thought that 1.6 was the Anniversary edition. Is there any way to get version 1.5, which is considered the Special Edition for mods?

No there isn't.

Darn, I didn't think so. gog should update the purchase page for Special Edition to say that you are really getting the Anniversary Edition.

Despite that, it's still great to have any version of Skyrim DRM free!

Actually you are not even getting that. GOG's version is 1.6.659.0, so any mods that inject .dll's will need to be made specifically for the GOG version.

It's easy to overlook, but in the announcement thread they did say that this was a GOG specific build of Skyrim.

Good luck, have fun
-SID

As far as I can tell, the Anniversary Edition is really just a package including the Special Edition & the paid Creation Club mods (i.e., Anniversary Upgrade). However, all the still-supported versions (PC & console) of the Special Edition seem to have gotten the free Anniversary update.

Bethesda could definitely have done better with the terminology here.