X0306 4 2017-10-03 0 0001629137 Global Blood Therapeutics, Inc. GBT 0001192591 HOMCY CHARLES J C/O GLOBAL BLOOD THERAPEUTICS, INC. 400 EAST JAMIE COURT, SUITE 101 SOUTH SAN FRANCISCO CA 94080 1 0 0 0 Common Stock 2017-10-03 4 S 0 0 0.00 D 0 I See Footnote Common Stock 2017-10-03 4 S 0 0 0.00 D 0 I See Footnote Common Stock 2017-10-04 4 S 0 0 0.00 D 0 I See Footnote Common Stock 2017-10-04 4 S 0 0 0.00 D 0 I See Footnote Common Stock 2017-10-04 4 S 0 0 0.00 D 0 I See Footnote Common Stock 2017-10-04 4 S 0 0 0.00 D 0 I See Footnote Common Stock 137728 D Common Stock 1600 I By Trust On October 3, 2017, Third Rock Ventures II, L.P. ("TRV II") sold 62,373 shares of Common Stock of the Issuer. The shares were sold at a weighted average price of $30.171. These shares were sold in multiple transactions at prices ranging from $29.75 to $30.55, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes (1), (4), (7), (9), (11) and (13) to this Form 4. After the transaction referenced in footnote (1), TRV II owned 1,273,032 shares. The reporting person is a partner of Third Rock Ventures GP II, L.P., which is the general partner of TRV II. The reporting person disclaims beneficial ownership over the shares held by TRV II, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares. On October 3, 2017, Third Rock Ventures III, L.P. ("TRV III") sold 72,463 shares of Common Stock of the Issuer. The shares were sold at a weighted average price of $30.171. These shares were sold in multiple transactions at prices ranging from $29.75 to $30.55, inclusive. After the transaction referenced in footnote (4), TRV III owned 213,250 shares. The reporting person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The reporting person disclaims beneficial ownership over the shares held by TRV III, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares. On October 4, 2017, TRV II sold 53,652 shares of Common Stock of the Issuer. The shares were sold at a weighted average price of $30.38. These shares were sold in multiple transactions at prices ranging from $29.60 to $30.60, inclusive. After the transaction referenced in footnote (7), TRV II owned 1,219,380 shares. On October 4, 2017, TRV III sold 62,332 shares of Common Stock of the Issuer. The shares were sold at a weighted average price of $30.38. These shares were sold in multiple transactions at prices ranging from $29.60 to $30.60, inclusive. After the transaction referenced in footnote (9), TRV III owned 150,918 shares. On October 4, 2017, TRV II sold 129,902 shares of Common Stock of the Issuer. The shares were sold at a weighted average price of $30.86. These shares were sold in multiple transactions at prices ranging from $30.65 to $31.15, inclusive. After the transaction referenced in footnote (11), TRV II owned 1,089,478 shares. On October 4, 2017, TRV III sold 150,918 shares of Common Stock of the Issuer. The shares were sold at a weighted average price of $30.86. These shares were sold in multiple transactions at prices ranging from $30.65 to $31.15, inclusive. After the transaction referenced in footnote (13), TRV III owned no shares. /s/ Charles Homcy 2017-10-05