ACES 2065-1 (linear, AP0) remains the core of ACES and is the only interchange and archival format (written to OpenEXRs conforming to SMPTE 2065-4).
The other color spaces - ACEScc, ACESproxy, ACEScct, ACEScg - are ephemeral working spaces that exist to meet very specific needs of real-world implementations. They are not intended to be written to files, stored, archived, or interchanged (possible exception: ACEScg might be written to files inside a VFX facility, but should be converted to ACES before sending out to another facility)
The color space names give a hint to their intended application. For example, ACEScg is a linear encoding used for CGI render and compositing. It uses a smaller set of primaries than ACES2065-1, specifically AP1, because tools used to synthetically render imagery (CGI) have long used certain optimizations that are different than in typical color management scenarios and sometimes do not work well with very wide-gamut primaries such as those defined in ACES2065-1.
Additionally, ACEScc is a logarithmic encoding intended for use in color correction systems whose controls expect a log relationship to relative scene exposures for proper operation. ACEScc also uses color primaries closer to achievable display primaries for more natural control with typical color grading. Because most color correction tools were built to operate on “log-like” data, the knobs and controls would feel “way off” if ACES were not converted to ACEScc, which is a space more suitable for color correction.
The additional color spaces are suggested spaces designed to allow one to remain within the ACES framework when using real-world production tools and workflows. Of course, one could choose to use alternate working spaces on-set, in VFX, and/or in the color corrector, but those choices would need to be managed carefully and poor choices will lead to poor results. ACEScc, ACEScct, ACESproxy, and ACEScg are ACES’ suggestions for color spaces that will hopefully support all production tools and workflows. Someone who knows what they’re doing can opt to use other color spaces within their workflow if it makes more sense - just don’t blame it on ACES if something breaks
To reiterate, linear ACES (i.e. encoded according to SMPTE 2065-1) is the only interchange and archival format (written to OpenEXRs conforming to SMPTE 2065-4).