From FB Sony A1 group Vegard Hanssen:
Got my a1, so I was out testing it today on birds. I have used the a9ii a lot for same types of images so here is what I think after one day.
1) a1 is much better to hold the focus on the bird when flying over the water. a9 will pick up the water much more often. Actually, I think the a1 only picked the water on wide focus once today. It sticks to the bird all the time. No problems with eagles picking up fish. With the a9 I need to be aware of where I have the bird in frame, but with a1 I can compose as I want, the focus sticks to the bird.
2) No problem with AF with birds flying straight towards me. Usually not a problem with a9 either, but I got eye AF when the bird got close enough with a1, instead of the beak which the a9 picks up.
3) Cropping in post gives me a much better result with a1 than a9, of course because of higher pixel count. But the image seems very sharp. So for me the result is much better with birds not close up.
4) The CFExpress cards flushes the buffer very fast. When using lossless compression I filled the buffer when the eagle descended. With lossy compression it was much easier to both take long series and flush the buffer.
5) It's much easier to fill the cards on a1 than a9. With the a9 I almost never fill the 2x128GB cards (10k images) on one day. With 2x160GB on a1 (5k images) I could easily fill both of them before the days is over.
6) The images on a1 with higher iso seems better than a9. Since I haven't tested this too much, I can't say for sure.
So all in all, I'm impressed with the a1. I add three images which is imported as raw in luminar 4. Luminar was able to edit the compressed files, but only shows thumbnails of lossless raws. These images are only cropped, no other changes to them. I'll give you better images later in the week when the weather is going to be better.