It's 12 nanometers. The Hisilent Kirin 710 is a 12-nanometer process processor that was released in the Huawei Nova 3i mobile phone in July 2018. The processor uses an 8-core design and is built by TSMC's 12nm process, which is also the first time Huawei has used TSMC's 12nm process, using a 448-core architecture with a maximum frequency of 2.2GHz.
The Huawei Kirin 710 uses a 14-nanometer chip.