The 20th International Conference on Augmenting Cognition in the AI-Accelerated Era, AC 2026, held as Part of the 28th HCI International Conference, HCI International 2026 (HCII 2026), took place in Montreal, QC, Canada, during July, 2026. A total of 7435 individuals from academia, research institutes, industry, and government agencies from 94 countries submitted contributions to HCII 2026. Following peer review, 1463 papers and 360 posters (as short research papers) are included in the volumes of the HCII 2026 proceedings published just before the start of the conference. This volume (LNAI 16709) of the HCII 2026 proceedings is dedicated to this year’s edition of the AC Affiliated Conference focusing on topics related to:·         AI and Augmented Cognition; Neuroergonomics and BCI; and Augmented Cognition in Complex Tasks and Environments.