UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

CASA SYSTEMS, INC.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

14713L102

(CUSIP Number)

April 18, 2022

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 14713L102

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CUSIP No. 14713L102

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CUSIP No. 14713L102

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CUSIP No. 14713L102

Casa Systems, Inc.

100 Old River Road

Andover, Massachusetts

Verizon Communications Inc. (“Verizon”)

Verizon Ventures LLC (“Verizon LLC”)

Verizon Investment Management Corp. (“Verizon Investment”)

Verizon:

Verizon Communications Inc.

1095 Avenue of the Americas

New York, New York 10036

Verizon LLC:

Verizon Ventures LLC

One Verizon Way

Basking Ridge, NJ 07920

Verizon Investment:

Verizon Investment Management Corp.

One Verizon Way

Basking Ridge, New Jersey 07920

See Item 4 of the cover pages attached hereto.

Common Stock, par value $0.001 per share

14713L102

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Not Applicable.

(a) Amount beneficially owned:

See Item 9 of the attached cover pages.

On April 18, 2022, Verizon LLC became the direct beneficial owner of 9,323,000 shares of Common Stock.

Verizon LLC is a direct wholly owned subsidiary of Verizon, and by virtue of this relationship, Verizon may be deemed to have shared power to vote and dispose of, or to direct the vote and disposition of, the 9,323,000 shares of Common Stock beneficially owned by Verizon LLC.

On October 1, 2021, October 4, 2021 and January 1, 2022, Verizon Investment acquired 4,700, 520 and 950 shares of Casa Systems, Inc., respectively. Verizon Investment is a direct wholly owned subsidiary of Verizon, and by virtue of this relationship, Verizon may be deemed to have shared power to vote and dispose of, or to direct the vote and disposition of, the 6,170 shares of Common Stock beneficially owned by Verizon Investment.

(b) Percent of class:

See Item 11 of the attached cover pages. Calculations of the percentage of shares of Common Stock beneficially owned are based on the 94,178,077 shares of Common Stock outstanding, consisting of (i) 9,323,000 shares of Common Stock newly issued to Verizon LLC on April 18, 2022 (the “Issuance”), plus (ii) 84,855,077 shares of Common Stock the issuer notified Verizon LLC in writing were outstanding at the close of business on the business day immediately preceding the Issuance.

(c) Number of shares as to which such person has:

(i) Sole power to vote or direct the vote:

See Item 5 of the attached cover pages.

(ii) Shared power to vote or direct the vote:

See Item 6 of the attached cover pages.

(iii) Sole power to dispose or to direct the disposition:

See Item 7 of the attached cover pages.

(iv) Shared power to dispose or to direct the disposition:

See Item 8 of the attached cover pages.

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following  ☐:

Not Applicable.

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Not Applicable.

Not Applicable.

Not Applicable.

Not Applicable.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

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SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this Statement is true, complete and correct.

Date: April 22, 2022

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Exhibit I

AGREEMENT

JOINT FILING OF SCHEDULE 13G

Each of the undersigned hereby agrees to file jointly the Schedule 13G to which this Agreement is attached, and any amendments to the Schedule 13G (the “Schedule 13G”) filed with respect to the common stock, par value $0.001 per share, of Casa Systems, Inc. which may be deemed necessary, pursuant to Regulation 13D-G under the Securities Exchange Act of 1934, as amended.

It is understood and agreed that each of the parties hereto is responsible for the timely filing of such statement and any future amendments to the Schedule 13G, and for the completeness and accuracy of the information concerning such party contained therein, but such party is not responsible for the completeness or accuracy of information concerning any other party unless such party knows or has reason to believe that such information is inaccurate.

It is understood and agreed that a copy of this Agreement shall be attached as an exhibit to the Schedule 13G, and any future amendments to the Schedule 13G, filed on behalf of each of the parties hereto.

Date: April 22, 2022

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