It can be confusing, because essentially, all versions of Kontakt are “players” of sample content. The biggest thing to remember: anytime you see mention of Kontakt Player, this simply refers to the free version.
It will be a mandatory upgrade, just not yet.
Many of us are able to get by just fine by still using Kontakt 5, however that will not always be the case, as developers take advantage of the new features and begin to release libraries that are only compatible with Kontakt 6. Kontakt 6 – This is the newest version of the Kontakt sampler, and it’s the latest and greatest, yet it’s benefits and features are yet to be fully taken advantage of, simply because it’s still so new on the market.