It's confusing, because 4k has been used as a term (not actually that often in practice) in the VFX industry for 5/6 years for the following resolutions:

4096 × 2160 (standard) 4096 x 3112 (super 35)

Then for 4k cameras, the following resolutions have become fairly common for "4k":

3840 x 2160 4096 x 2304

so these days, it's difficult to know what's been talking about...