If you mean Google Adiantum, it was merged into Linux mainline in December 2018. I'm not sure which kernel version it ended up in, but we will be able to get it with a future kernel upgrade. Kernel 4.19.x, which is currently shipping, is too old.
Edit: of course, you might as well just run mainline kernels (at least up to Pi 3B+) and use Adiantum now. It should work.