X0306 4/A 2021-02-23 2021-02-25 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 Restricted Stock Units 2021-02-23 4 A 0 119834 0.00 A Common Stock 119834 119834 D The original Form 4, filed February 25, 2021, is being amended by this Form 4 amendment solely to correct an administrative error related to the disclosure of the vesting schedule for 23,967 of the shares underlying this award. Due to an administrative error, those shares were reported as being subject to time-based vesting criteria instead of performance-based vesting criteria. Each Restricted Stock Unit ("RSU") represents the right to receive one share of common stock, $0.001 par value per share (the "Common Stock") of Casa Systems, Inc. (the "Company") upon vesting, subject to the reporting person's continued service relationship with the Company and the other terms and conditions set forth in the applicable RSU agreement. In the sole discretion of the Company's board of directors, the Company may, with respect to any applicable vesting date, deliver to the reporting person Common Stock or cash having a fair market value equal to the number of shares of Common Stock underlying the portion of the RSU that vested on such date, payable within 30 days of the vesting date, less applicable taxes. The award consists of two separate issuances of RSUs. The first issuance of 95,867 RSUs are subject to time-based vesting and are scheduled to vest over four years, with 25% of the shares underlying the award vesting on January 1, 2022, and 25% of the shares underlying the award vesting at the end of each successive one-year period thereafter. The second issuance of 23,967 RSUs are subject to performance-based vesting, the conditions for which are met upon the Company's level of achievement of pre-established performance parameters, as approved by the Company's Board of Directors, related to either or both of (i) the Company's relative Total Shareholder Return ("TSR") performance against the TSR of the companies listed in the Russell 2000 Index, and (ii) the absolute stock price performance of the Company's common stock, in each case, (continued from footnote 3) measured over the three-year period beginning on January 1, 2021 and ending on January 1, 2024, and subject to the other terms and conditions set forth in the applicable RSU agreement. These RSUs have no expiration date. /s/ Timothy Rodenberger, as Attorney-in-Fact 2021-05-05