As first reported on the arc-spec.org website, on October 2nd the IETF’s DMARC Working Group published version 18 of the ARC specification document, incorporating the changes suggested during the Working Group Last Call (WGLC). There are many small language changes to clarify concepts or bring usage in line with other IETF documents, such as Email Address Internationalization (EAI).
You can review the changes between the pre- and post-WGLC versions using this link.