The folks over at Imaging Resource tried to make the A9 overheat in very unfavorable conditions:
It is extremely challenging to overheat the A9. I say that as even though I was actually trying to make the camera overheat, I could not.
So we can put the “a9 overheating” story at peace. It also seems like that few of the testers who experienced the overheating in extreme conditions were also using slow SD cards which of course does keep the processor running for a long time to clear the buffer.
Therefore, if you buy the A9 make the wise choice to buy fast cards too:
Sony SF-G 128GB: BHphoto, Adorama, Amazon. In EU: AmazonDE, AmazonUK, AmazonFR, AmazonIT, AmazonES.
Sony SF-G 64GB: BHphoto, Adorama, Amazon. In EU: AmazonDE, AmazonUK, AmazonFR, AmazonIT, AmazonES.
Sony SF-G 32GB: BHphoto, Adorama, Amazon.
Sony A9:
Sony A9 at BHphoto, Adorama, Amazon, BestBuy. FocusCamera. Calumet.de. Park UK. Wex UK. Jessops.
Sony A9 with Grip Extension Kit at BHphoto, Adorama and Amazon.