0002022626 2026-08-11 2026-08-11 false 0002022626 8-K 2026-08-11 UPSTREAM BIO, INC. DE 001-42366 38-4187694 890 Winter Street Suite 200 Waltham MA 02451 (781) 208-2466 Not Applicable false false false false Common Stock, $0.001 par value per share UPB NASDAQ true false