I just received a new Archer AX55 from Amazon. It is shown as V1.6. However, on the firmware download site I see that versions V1 and V2.6 are listed, with the firmware date for V2.6 listed as publish

EDIT: I changed the title to reflect my recent findings (see last post at the bottom). I just got an AX55 to replace an old NetGear R6400 since I wanted the benefits of Wi-Fi 6, but almost immediately