100% it's OEM, every chinese phone is built by some "you never heard about" company and later rebranded as Xiaomi or whatever. Does it matter though? With big

100% it's OEM, every chinese phone is built by some "you never heard about" company and later rebranded as Xiaomi or whatever. Does it matter though? With big enough leverage OEM will provide docs and will adapt hardware. That will cost extra, of course.