This proceedings volume, the sixth in a series from the Combinatorial and Additive Number Theory (CANT) conferences, is based on talks from the 20th and 21st annual workshops, held in New York in 2022 (virtual) and 2023 (hybrid) respectively. Organized every year since 2003 by the New York Number Theory Seminar at the CUNY Graduate Center, the workshops survey state-of-the-art open problems in combinatorial and additive number theory and related parts of mathematics.In this volume, the reader will find peer-reviewed and edited papers on current topics in number theory. This selection of articles will be of relevance to both researchers and graduate students interested in current progress in number theory.