The O Developer Preview release on Pixel uses 'normal' lz4... Or at least it succeeds in booting with it recompressed in the new format. Anything else, I don't know.
If it doesn't work with a specific popular kernel that has an edition for one of my test devices, do let me know.
Edit: Nevermind, I see it's just the kernel that's compressed with LZ4 in Pixel's ODP, not the ramdisk. You'll probably want to support the legacy format though, since that's what Linux uses and the reason it's still included in LZ4:
-l : compress using Legacy format (Linux kernel compression)