The Chandra X-Ray Center has done standard testing with CIAO 4.13 on macOS 11 (Big Sur) running on the Intel chip and the new Apple M1 chip using Apple's Rosetta2 emulation layer to provide support for this architecture. Overall users can expect most of CIAO to work correctly on both platforms.
A summary of the issues found for the M1 chips is given on the CIAO Platform Support page. In particular there is a known issue with the version of matplotlib (3.2) which is included in the ciao-install edition. Users will need to upgrade matplotlib to make plots using sherpa. There is currently no estimate for the date of a native M1 CIAO release.