With productions needing UHD deliverables, the AMIRA will now offer the ability to record all ProRes codecs in Ultra High Definition.

ARRI Group: ARRI announces ProRes UHD output for AMIRA (http://www.arri.de/about_arri/press/english/english_single/?tx_ttnews)[tt_news]=1664&tx_ttnews[backPid]=7581&cHash=b5e1e534809b25789e921c2e46655a47

Although not having a 4k sensor, the Arri cameras have been the camera of choice on many productions that receive a 4k distribution.

http://www.redsharknews.com/technology/item/1953-shock-amira-uhd-announcement-will-shake-the-world-of-4k-to-its-roots

Hmmm - may be a question of where you draw lines, but it's not really UHD though, is it?

Not in numbers terms, I gather from an Arri rep:

"AMIRA ProRes UHD is upscaled in-camera based on 3200 x 1800 photo sites on
the sensor. This is about the 16:9 area plus the surround view area" not the Arri Raw Open Gate that uses 3414 x 2198.

Apparently they will be doing a big screen presentation at IBC.

EDIT a bit more: http://www.fdtimes.com/2014/08/26/prores-uhd-for-amira/

It looks like there will also be an upgrade available for the Alexa, but ProRes 3.2K.: ARRI Alexa 3.2K ProRes for UHD | Film and Digital Times (http://www.fdtimes.com/2014/09/02/arri-alexa-3-2k-prores/)