Do you mean the 64 bit testing image?
https://os.zynthian.org/test/2023-08-22-zynthianos-bullseye-arm64-testing-2308.zip
It’s a work in progress and still needs some extra work. Also, we will jump to bookworm.
But you can try it if you like to be in the cutting edge. It’s 95% functional and “quite stable”, indeed! 
Regards!