[leorize]

I believe the phrasing might not be clear to everyone, so here's a reduced version:

* Nim's current async implementation creates a lot of cycles in the graph, so ARC can't collect them.

* ORC is then developed as ARC + cycle collector to solve this issue, and it has been a success.

* This 1.4 release introduces ORC to everyone so that we can have mass testing for this new GC and eventually move torwards ORC as the default GC.

TL;DR: ORC works with everything† and will be the new default GC in the future. Your old Nim code will continue to work, and will just get faster‡.

† We are not sure that it's bug-free yet, which is why it's not the default for this release.

‡ Most of the time ORC speeds things up, but there are edge cases where it might slow things down. You're encouraged to test your code with --gc:orc against our default GC and report performance regressions.

[treeform]

Your explanation is very clear. Thanks.