After a long development and testing cycle, alongside refinement of the draft protocol itself, an alpha version of an open source implementation of the ARC protocol has been released. Congratulations to the volunteers from across the globe who contributed to this effort over the years.
ARC allows forwarders and mailing lists to convey message authentication results that would otherwise be lost, which can present challenges to some DMARC adopters. OpenARC v0.1.0 is at https://github.com/trusteddomainproject/OpenARC/releases.
An overview of how the ARC protocol works, and in what situations it would be deployed, is available in the presentation ARC Protocol Overview