MARC 21 update no. 29 (November 2019) is now available on the MARC website (www.loc.gov/marc/). It is integrated into the documentation for each of the Online Full and Concise formats that are maintained on that site -- the Bibliographic format, Authority format, Holdings format, Classification format, and Community Information format. The documentation includes changes made to the MARC 21 formats resulting from proposals which were considered by the MARC 21 community since the publication of Update No. 28 (May 2019).
The changes are indicated in red. Each format also has an appendix, "Format Changes for Update No. 29 (November 2019)" that lists the changes that comprise the update… Users are not expected to begin using the new features in the format until 60 days from the date of this announcement: November 26, 2019. For more information about format documentation see: http://www.loc.gov/marc/status.html.
Full text here.