http://www.desipro.de/ddwrt/K4-AC-ALPINE/

Readme:

R9000 build: Flash R9000-factory-to-ddwrt.img build from Netgear firmware. Once dd-wrt is running you have to use ddwrt-netgear-R9000.bin to flash future updates. Currently known issue: -2G and 5G leds are not operational since they cannot be controlled through gpio. Current opensource wireless driver has no support to control these leds. -60G interface info is currently not correctly display in status pages and due to missing 60G client, 60G operation is untested If you want to revert to netgear firmware flash: ddwrt-to-netgear-fw-R9000.bin