This blog is updated daily.
A general description is here.
Environment variable ‘R_SYSTEM_ABI’ is no longer used and so no longer recorded in ‘etc/Renviron’ (it was not on Windows and was only ever used when preparing package ‘tools’).
(In progress) A new ‘configure’ option ‘--with-newAccelerate’ makes use of Apple's ‘new’ BLAS / LAPACK interface in their Accelerate framework. That interface is only available in macOS 13.3 or later, and building requires SDK 14.3 or later (from the Command Line Tools or Xcode).
To avoid many compilation warnings you may need to use
CC="clang -mmacos-version-min=13.3"
That version of Accelerate provides LAPACK 3.9.1 rather than 3.2.1.
Currently Accelerate is used for BLAS calls from C in R and package stats and for LAPACK calls from the ‘lapack’ module.
The BLAS entry points in libRblas.dylib are diverted to Accelerate: this means that calls to LAPACK routines from packages will go to the reference implementation and BLAS calls in that will use Accelerate.