Updated - Amped Wireless has announced its first 4x4 AC router.
Updated 1/5/15 - Amped joined the rest of the crowd and changed to using AC2600 like the rest of the new batch of Qualcomm-based 4x4 routers introduced at CES 2015. Numbers have been adjusted accordingly.
RTA2550 RTA2600 "Athena" HighPower AC2550 Wi-Fi Router with MU-MIMO is the first 4x4 AC router with a 2.4 GHz 4x4 radio supporting a maximum link rate of 800 Mbps when used in 40 MHz bandwidth mode.
Combined with a 1733 Mbps maximum 5 GHz band rate, yields a total of 2533 Mbps, which has been rounded up to obtain the
AC2550 AC2600 class moniker.
Amped Wireless RTA2550
Amped describes the router as "packed with cutting-edge multi-user MIMO technology". But we'll have to wait and see if it actually ships with MU-MIMO enabled. Other 4x4 AC routers, based on Quantenna's 4x4 chipset, have yet to enable MU-MIMO.
Other features include Gigabit WAN (1) and switched LAN (4) ports, one each USB 2.0 and 3.0 ports for storage sharing, "updated" user interface, guest networks, adjustable coverage controls, parental controls and IPv6 support.
RTA2550 RTA2600 isn't priced yet and won't ship until "mid-2015".