X0306 4 2020-07-01 0 0001280600 ACCELERON PHARMA INC XLRN 0001690773 Dable Habib J 128 SIDNEY STREET CAMBRIDGE MA 02139 1 1 0 0 CEO and President Common Stock 2020-07-01 4 M 0 50000 35.04 A 139324 D Common Stock 2020-07-01 4 S 0 3700 93.53 D 135624 D Common Stock 2020-07-01 4 S 0 3000 94.46 D 132624 D Common Stock 2020-07-01 4 S 0 13047 95.85 D 119577 D Common Stock 2020-07-01 4 S 0 15219 96.49 D 104358 D Common Stock 2020-07-01 4 S 0 9534 97.43 D 94824 D Common Stock 2020-07-01 4 S 0 4400 98.57 D 90424 D Common Stock 2020-07-01 4 S 0 1100 99.42 D 89324 D Option to Purchase Common Stock 35.04 2020-07-01 4 M 0 50000 0 D 2026-12-01 Common Stock 50000 350000 D The reported transactions were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $93.06 to $94.02 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., 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 range set forth in this footnote (2) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $94.06 to $94.97 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., 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 range set forth in this footnote (3) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $95.10 to $96.09 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., 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 range set forth in this footnote (4) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $96.10 to $97.09 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., 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 range set forth in this footnote (5) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $97.10 to $98.01 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., 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 range set forth in this footnote (6) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $98.18 to $99.08 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., 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 range set forth in this footnote (7) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $99.20 to $99.61 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., 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 range set forth in this footnote (8) to this Form 4. The shares of common stock underlying this stock option award vested as to 25% of the shares on December 1, 2017, the first anniversary of the grant, and the remainder vest in equal quarterly installments over the three years thereafter. /s/ Adam M. Veness, as attorney-in-fact for Habib J. Dable 2020-07-06