This book constitutes the refereed post-conference proceedings of the 6th International Conference for Next Generation Arithmetic, CoNGA 2025, held in St. Louis, MO, USA, during November 14-15, 2025.

The 10 full papers presented in this volume were carefully reviewed and selected from 18 submissions. CoNGA 2025 deals with all aspects of Next Generation Arithmetic, focusing on alternative computer arithmetic, such as unums and posits, to enhance high-performance computing.