Quoting Christopher Dawson of OCLC:
“This Technical Bulletin covers all of the Library of Congress’s MARC Update 10 and most of MARC Update 11 (exceptions are noted). Many of these changes relate to the WorldCat testing of Resource Description and Access (RDA), the proposed successor to AACR2. Also covered are comments and requests from OCLC users and staff.
“Implementations of the OCLC-MARC updates covered in the Technical Bulletin may occur in stages, which OCLC will announce via logon Messages of the Day, Connexion News, and the OCLC-CAT listserv. It is recommended that users not begin to use the new capabilities, fields and subfields, indicators, practices, and codes until OCLC announces that they may be used.”
A list of Technical Bulletins currently in force can be found here.
(Cross-posted at Three Catalogers Walk Into a Blog.)