Hikvision have released V4.21.005 for their K-series NVRs (only 76 77 86 NI-K2 K4 K8) , which you can download from the UK portal here:
HIKVISION UK PORTAL
I have checked:
Hikvision Officially Release V4 Firmware for their K-Series NVRs - V4.21.005
HIKVISION UK PORTAL
I have checked:
Is this correct?
V4 firmware for the K-series NVRs at the UK...
Hikvision Officially Release V4 Firmware for their K-Series NVRs - V4.21.005