Indeed, the specs page says all 3 have HDMI 2.1 and 3x DisplayPort 1.4a: https://www.nvidia.com/en-eu/geforce/graphics-cards/30-serie...

However, Wikipedia says it’s capable of 8k with a proprietary lossy video codec called Display Stream Compression:

DSC is a "visually lossless" encoding technique with up to a 3:1 compression ratio. Using DSC with HBR3 transmission rates, DisplayPort 1.4 can support 8K UHD (7680 × 4320) at 60 Hz

The quote is from there: https://en.wikipedia.org/wiki/DisplayPort#1.4