It's v9 not because of major changes, but because for a while now Qemu has used year-based major versions (ver = year-2015), and this is the first release of 2024.

Perhaps this bears repeating here:

    Running QEMU with KVM requires Linux 4.4 or newer. A future version of QEMU will increase the minimum requirement for Arm hosts to Linux 4.19 (also when running KVM); if this is too restrictive for your use case, please contact us at qemu-devel@nongnu.org.

Linux v4.19 is EOL at the end of the year, whoever is still using it should really be looking to upgrade, they're running out of time.

v4.4 is already EOL as far as the main Linux kernel developers are concerned.

How is x86_64 GDB debugging support nowadays in Qemu? Years ago, with osdev wiki in hand, I tried developing a kernel with assembly, and got as far as 32-bit but never got around to 64-bit because GDB debugging was not supported for 64-bit qemu.

It works fine, I use it all the time for my hobby OS development.