Sony has its eye on the extreme prize with the 4k-enabled X1000V action camera.
Hands on new Sony 4K & AS200V Action Cams - Video, Stills & Tech Details - Bikerumor
Sony FDR-X1000V/W 4K Action Cam : Electronics
Sony 4K Action Cam Hands-On: Giving GoPro A Run For Its Money
Sony FDR-X1000v 4K Action Cam Review - Videomaker
Excellent!!]Sony FDR-X3000 Camcorder/Action Cam w/some accessories
Sony FDR-X1000v 4K Action Cam Review - Videomaker
Sony FDR-X1000V 4K Action Cam FDRX1000V/W B&H Photo Video
Sony HDR-AS200VR/W Action Cam + Live View Remote Kit : Electronics
Sony FDR-X1000VR 4K Action Cam and Live-View Remote Review - Singletracks Mountain Bike News
Sony 4K Action Cam FDR-X1000V First Impressions Review - Reviewed
2016 Roundup: 4K action cameras: Digital Photography Review
Sony 4K Action Cam Review (FDR-X1000V)