These new cameras keep the 3.4K ALEV III sensor of the previous ALEXAs and add ALEXA 65 electronics and AMIRA color management. While the rumors of a new 6K Super 35mm sensor could still turn out to be true, these new cameras will use the same sensor as the previous ALEXA models, but feature completely new processing internally, including the ability to record in-camera UHD ProRes (3840 x 2160) like the AMIRA, and also the ability to do true 4K ProRes (slightly above actually at 4096 x 2637 because of the more square sensor). It's worth noting that these will be upscaled resolutions, as the sensor maxes out below 4K.

The new camera bodies will also include optional noise reduction, so it's possible that the ALEXA will be able to be pushed a little bit further in low-light situations right in camera without needing to do much more in post. The SXT line retains the Open Gate, 4:3, and 16:9 sensor modes, all of which can all be recorded in ARRIRAW or ProRes:

The first ALEXA SXT cameras are planned for release around mid-2015; the full range will comprise ALEXA SXT EV, SXT Plus and SXT Studio models, replacing current ALEXA XT cameras (though the ALEXA Classic EV model will remain in the line-up). ALEXA XT cameras (except ALEXA XT M) shipped between 1st Jan. 2015 and the first shipment of SXT cameras will be eligible for a full SXT upgrade, free of charge. 


Here are some of the major new features:

  • Easy in-camera ProRes 4K recording
    • ProRes 4K UHD (3840 x 2160)
    • ProRes 4K Cine (4096 x 2637)
  • Improved image quality
    • Completely overhauled image processing chain
    • Advanced pixel correction
    • Optional noise reduction
  • New Looks and smoother workflow
    • 3D Look-up Tables, ASC Color Decision List, Rec 2020 gamma
    • Matches current ALEXA images, but provides basis for radically different looks
    • Improved on-set preview, more efficient dailies and faster final grading
    • Same tools for ALEXA SXT, ALEXA Mini & AMIRA
  • Super flexible on-set monitoring
    • Three fully independent HD-SDI outputs

The new SXT will also sport new media (hat tip to Jon Fauer) called SXR drives developed with Codex (adapters let you use the old capture drives), which can support up to 20Gb/s and come in sizes up to 2TB at launch. 


A look at the adapters possible with the new media bay (SXR, XR, SxS, CFast):


And here's more on the new color management:

A new type of look file, the ALF-2 (ARRI Look File 2), contains an ASC CDL (Color Decision List) as well as a 3D LUT (Look-Up Table). The new color management engine can easily match the look of current ALEXA cameras, but also provides the basis for radically different looks. In addition, previewing of looks on set is improved, including the option to use the wide color gamut of Rec 2020 gamma, while dailies creation is made more efficient and final grading made faster. ALF-2 files and the tools that create them are compatible between ALEXA SXT, ALEXA Mini and AMIRA.

The three HD-SDI outputs will allow different color profiles as well:

To further streamline on-set workflows and deliver what has been asked for by crews all over the globe, ALEXA SXT cameras include three fully independent HD-SDI outputs. This allows, for instance, a Log C image to be used to show the director a pristine image with live grading, a clean Rec 709 image to be fed to video village, and a Rec 709 image with status information overlays to be displayed on the camera's on-board monitor. 

If you've got a slightly older XT camera and you don't benefit from the free SXT upgrade, ARRI will be offering an SXR module for these cameras which will provide all of the same features, but may not be upgradeable in the future.

While it's unclear if there will be any more announcements from ARRI besides the SXT and the ALEXA Mini before NAB 2015, it's clear that ARRI is trying to get quite a bit out of this current sensor, and DPs are still very happy with the images they are getting. 

Source: ARRI SXT Overview