Xiaomi's mixed record for releasing kernel sources continues, as the company has still not posted sources for the Mi A1. While Xiaomi has previously stated their internal goal for releasing kernels is "within three months," according to XDA-Developers, the Mi A1 is well past this mark, as it was released last September. With the apparent end of the Nexus device program, the Mi A1 would be a prime candidate for custom ROM development, in place of the 2+ year old Nexus 5X.

Xiaomi has had a rather tortured past with GPL compliance. While the company had released sources for recent Redmi phones in a timely manner, prior phones such as the Mi3 had been subject to half-year delays. Being an Android One device, it should be held to a higher standard.

For the record, Sharp, Kyocera, and HTC have released kernel sources for their Android One phones. Motorola has but one Android One phone—the Moto X4—for which sources have also been released.

Source: XDA Developers (1, 2)