Despite its generally fast-moving nature, the kernel project relies on a
number of old tools. While critics like to focus on the community’s
extensive use of email, a possibly more significant anachronism is the use
of the 1989 version of the C language standard for kernel code — a standard
that was codified before the kernel project even began over 30 years ago.
It is looking like that longstanding practice could be coming to an end as
soon as the 5.18 kernel, which can be expected in May of this year.

Source: LWN.net – [$] Moving the kernel to modern C