X0508 4 2024-03-20 false 0001860782 2seventy bio, Inc. TSVT 0001866219 Newton Charles W. 60 BINNEY STREET CAMBRIDGE MA 02142 true false false false false Common Stock 2024-03-20 4 A false 16600.00 0.00 A 16600.00 D Stock Options (Right to buy) 4.54 2024-03-20 4 A false 33400.00 0.00 A 2034-03-20 Common Stock 33400.00 33400.00 D This restricted stock unit award vests ratably over three years in annual installments with the first installment vesting on March 20, 2025, subject to the Reporting Person's continued service through the applicable vesting date. This stock option vests ratably over three years in annual installments with the first installment vesting on March 20, 2025, subject to the Reporting Person's continued service through the applicable vesting date. /s/ Iya Kessler, Attorney-in-Fact 2024-03-25