X0306 4 2021-09-07 0 0001333835 Casa Systems Inc CASA 0001723982 Chen Weidong C/O CASA SYSTEMS, INC. 100 OLD RIVER ROAD ANDOVER MA 01810 0 1 0 0 Chief Technology Officer Common Stock 2021-09-07 4 S 0 65000 7.12 D 2140361 D Common Stock 2021-09-08 4 S 0 45000 6.88 D 2095361 D The sales reported in this Form 4 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 $7.01 to $7.26, inclusive. The reporting person undertakes to provide to Casa Systems, Inc., any security holder of Casa Systems, 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 ranges set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $6.82 to $7.01, inclusive. The reporting person undertakes to provide to Casa Systems, Inc., any security holder of Casa Systems, 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 ranges set forth in this footnote. /s/ Timothy C. Rodenberger, as Attorney-in-Fact 2021-09-09