X0609 4 2026-04-24 0001979330 NB Bancorp, Inc. NBBK 0002003622 Lynch Christopher R. false 1063 GREAT PLAIN AVE NEEDHAM MA 02492 1 0 Common Stock 2026-04-24 4 F 0 4150 19.82 D 92772 D Common Stock 60000 I By IRA Includes shares of restricted stock which vest at a rate of 20% per year commencing on April 24, 2026. Includes shares of restricted stock which vest 100% on January 2, 2027. /s/ Steven Lanter, pursuant to power of attorney 2026-04-27