I am trying to decide between two Netgear routers.

[enichante]

Costco has the NETGEAR Nighthawk 6-Stream AX4300 for $130, down from $200 right now.

It says it's wifi six but the details show up to 802.11 ac

Is this some sort of strange advertising issue?

I'm looking at another similar wifi router from the same line that's newer and more expensive.

Netgear Nighthawk AX4200, which appears to be a true wifi 6 router with 802.11ax.

[FURRYe38]

Are you referring to this model router? 

https://www.netgear.com/support/product/rax45.aspx

It supports AX modes, along with older wifi modes like AC and N. 

[DNB09876]

DNB= do not buy this crap. 2 years old, and they are done with you…after the first 6 months of purchase. They give you no customer service they give you no ways to fix things they just cut you off. Just saying messages will be after learning the hard way do not buy their crap!

[FURRYe38]

Other router mfrs have similar warranty policies.