Document:

EX-10.4

 Exhibit 10.4 

CASA SYSTEMS, INC. 
 Nonstatutory
Stock Option Agreement 
 Granted Under 2003 Stock Incentive Plan 

1. Grant of Option. 
 This agreement
evidences the grant by Casa Systems, Inc., a Delaware corporation (the “Company”), on                     ,
200     (the “Grant Date”) to                     , an employee, consultant or director of the Company
(the “Participant”), of an option to purchase, in whole or in part, on the terms provided herein and in the Company’s 2003 Stock Incentive Plan (the “Plan”), a total of
             shares (the “Shares”) of common stock, $.001 par value per share, of the Company (“Common Stock”) at
$             per Share. Unless earlier terminated, this option shall expire on
                     (the “Final Exercise Date”). 

It is intended that the option evidenced by this agreement shall not be an incentive stock option as defined in Section 422 of the Internal
Revenue Code of 1986, as amended, and any regulations promulgated thereunder (the “Code”). Except as otherwise indicated by the context, the term “Participant”, as used in this option, shall be deemed to include any person
who acquires the right to exercise this option validly under its terms. 
 2. Vesting Schedule. 

This option will become exercisable (“vest”) as to 25% of the original number of Shares on the first anniversary of the Vesting
Commencement Date (as defined below) and as to an additional 2.0833% of the original number of Shares at the end of each successive one-month period following the first anniversary of the Vesting Commencement Date until the fourth anniversary of the
Vesting Commencement Date. For purposes of this Agreement, the “Vesting Commencement Date” shall mean                     ,
200    . 
 The right of exercise shall be cumulative so that to the extent the option is not exercised in any
period to the maximum extent permissible it shall continue to be exercisable, in whole or in part, with respect to all shares for which it is vested until the earlier of the Final Exercise Date or the termination of this option under Section 3
hereof or the Plan. 
 3. Exercise of Option. 

(a) Form of Exercise. Each election to exercise this option shall be accompanied by a completed Notice of Stock Option Exercise in
the form attached hereto as Exhibit A, signed by the Participant, and received by the Company at its principal office, accompanied by this agreement, and payment in full in the manner provided in the Plan. The Participant may purchase
less than the number of shares covered hereby, provided that no partial exercise of this option may be for any fractional share or for fewer than ten whole shares. 

(b) Continuous Relationship with the Company Required. Except as otherwise provided in this Section 3, this option may not be
exercised unless the Participant, at the time he or she exercises this option, is, and has been at all times since the Grant Date, an employee, officer or director of, or consultant or advisor to, the Company or any parent or subsidiary of the
Company as defined in Section 424(e) or (f) of the Code (an “Eligible Participant”). 

 (c) Termination of Relationship with the Company. If the Participant ceases to be an
Eligible Participant for any reason, then, except as provided in paragraphs (d) and (e) below, the right to exercise this option shall terminate three months after such cessation (but in no event after the Final Exercise Date), provided
that this option shall be exercisable only to the extent that the Participant was entitled to exercise this option on the date of such cessation. Notwithstanding the foregoing, if the Participant, prior to the Final Exercise Date, violates
the non-competition or confidentiality provisions of any employment contract, confidentiality and nondisclosure agreement or other agreement between the Participant and the Company, the right to exercise this option shall terminate immediately upon
such violation. 
 (d) Exercise Period Upon Death or Disability. If the Participant dies or becomes disabled (within the meaning of
Section 22(e)(3) of the Code) prior to the Final Exercise Date while he or she is an Eligible Participant and the Company has not terminated such relationship for “cause” as specified in paragraph (e) below, this option shall be
exercisable, within the period of one year following the date of death or disability of the Participant, by the Participant (or in the case of death by an authorized transferee), provided that this option shall be exercisable only to
the extent that this option was exercisable by the Participant on the date of his or her death or disability, and further provided that this option shall not be exercisable after the Final Exercise Date. 

(e) Discharge for Cause. If the Participant, prior to the Final Exercise Date, is discharged by the Company for “cause” (as
defined below), the right to exercise this option shall terminate immediately upon the effective date of such discharge. “Cause” shall mean willful misconduct by the Participant or willful failure by the Participant to perform his or her
responsibilities to the Company (including, without limitation, breach by the Participant of any provision of any employment, consulting, advisory, nondisclosure, non-competition or other similar agreement between the Participant and the Company),
as determined by the Company, which determination shall be conclusive. The Participant shall be considered to have been discharged for “Cause” if the Company determines, within 30 days after the Participant’s resignation, that
discharge for cause was warranted. 
 4. Right of First Refusal and Restrictions on Transfer. 

(a) If the Participant proposes to sell, assign, transfer, pledge, hypothecate or otherwise dispose of, by operation of law or otherwise
(collectively, “transfer”) any Shares acquired upon exercise of this option, then the Participant shall first give written notice of the proposed transfer (the “Transfer Notice”) to the Company. The Transfer Notice shall name the
proposed transferee and state the number of such Shares the Participant proposes to transfer (the “Offered Shares”), the price per share and all other material terms and conditions of the transfer. 

(b) For 60 days following its receipt of such Transfer Notice, the Company shall have the option to purchase some or all of the Offered Shares
at the price and upon the terms set forth in the Transfer Notice. In the event the Company elects to purchase any Offered Shares (the Offered Shares to be purchased by the Company hereunder are referred to as the “Purchased

  
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Shares”), it shall give written notice of such election to the Participant within such 60-day period. Within 10 days after his receipt of such notice, the Participant shall tender to the
Company at its principal offices the certificate or certificates representing the Purchased Shares, duly endorsed in blank by the Participant or with duly endorsed stock powers attached thereto, all in a form suitable for transfer of the Purchased
Shares to the Company. Promptly following receipt of such certificate or certificates, the Company shall deliver or mail to the Participant a check in payment of the purchase price for the Purchased Shares; provided that if the terms
of payment set forth in the Transfer Notice were other than cash against delivery, the Company may pay for the Purchased Shares on the same terms and conditions as were set forth in the Transfer Notice; and provided further that any
delay in making such payment shall not invalidate the Company’s exercise of its option to purchase the Purchased Shares. 
 (c) If the
Company does not elect to acquire all of the Offered Shares, the Participant may, within the 30-day period following the expiration of the option granted to the Company under subsection (b) above, transfer the Offered Shares (other than the
Purchased Shares) to the proposed transferee, provided that such transfer shall not be on terms and conditions more favorable to the transferee than those contained in the Transfer Notice. Notwithstanding any of the above, all Offered
Shares transferred to a third party pursuant to this Section 4 shall remain subject to the right of first refusal and transfer restrictions set forth in this Section 4 and such transferee shall, as a condition to such transfer, deliver to the
Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of this Section 4. 

(d) After the time at which the Purchased Shares are required to be delivered to the Company for transfer to the Company pursuant to
subsection (b) above, the Company shall not pay any dividend to the Participant on account of such Purchased Shares or permit the Participant to exercise any of the privileges or rights of a stockholder with respect to such Purchased Shares, but
shall, in so far as permitted by law, treat the Company as the owner of such Purchased Shares. 
 (e) The following transactions shall be
exempt from the provisions of this Section 4: 
 (1) any transfer of Shares to or for the benefit of the Participant’s spouse or any of
his or his spouse’s parents, children, siblings, nieces, nephews or grandchildren, or to a trust or similar entity for their benefit; 

(2) any transfer pursuant to an effective registration statement filed by the Company under the Securities Act of 1933, as amended (the
“Securities Act”); and 
 (3) any transfer made as part of the sale of all or substantially all of the shares of capital stock of
the Company (including pursuant to a merger or consolidation); 
 provided, however, that in the case of a transfer pursuant to clause (1)
above, such Shares shall remain subject to the right of first refusal and transfer restrictions set forth in this Section 4 and such transferee shall, as a condition to such transfer, deliver to the Company a written instrument confirming that such
transferee shall be bound by all of the terms and conditions of this Section 4. 

  
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 (f) The Company may assign its rights to purchase Offered Shares in any particular transaction
under this Section 4 to one or more persons or entities. 
 (g) The provisions of this Section 4 shall terminate upon the earlier of the
following events: 
 (1) the closing of the sale of shares of Common Stock in an underwritten public offering pursuant to an effective
registration statement filed by the Company under the Securities Act; or 
 (2) the sale of all or substantially all of the outstanding
shares of capital stock, assets or business of the Company, by merger, consolidation, sale of assets or otherwise (other than a merger or consolidation in which all or substantially all of the individuals and entities who were beneficial owners of
the Common Stock immediately prior to such transaction beneficially own, directly or indirectly, more than 50% of the outstanding securities entitled to vote generally in the election of directors of the resulting, surviving or acquiring corporation
in such transaction). 
 (h) The Participant shall not transfer any Shares, or any interest therein, to any person or entity that is a
competitor of the Company, as determined by the Board of Directors of the Company in its sole discretion, unless such transfer is made in connection with the sale of all or substantially all of the capital stock, assets or business of the Company,
by merger, consolidation, sale of assets or otherwise. 
 (i) The Company shall not be required (a) to transfer on its books any of the
Shares which shall have been sold or transferred in violation of any of the provisions set forth in this Section 4, or (b) to treat as owner of such Shares or to pay dividends to any transferee to whom any such Shares shall have been so sold or
transferred. 
 (j) The certificate representing Shares shall bear a legend substantially in the following form (in addition to, or in
combination with, any legend required by applicable federal and state securities laws and agreements relating to the transfer of the Company securities): 

“The shares represented by this certificate are subject to a right of first refusal in favor of the Company, as provided in a certain stock option
agreement with the Company.” 
 5. Agreement in Connection with Public Offering. 

The Participant agrees, in connection with the initial underwritten public offering of the Company’s securities pursuant to a
registration statement under the Securities Act, (i) not to sell, make short sale of, loan, grant any options for the purchase of, or otherwise dispose of any shares of Common Stock held by the Participant (other than those shares included in the
offering) without the prior written consent of the Company or the underwriters managing such initial underwritten public offering of the Company’s securities for a period of 180 days from the effective date of such registration statement, and
(ii) to execute any agreement reflecting clause (i) above as may be requested by the Company or the managing underwriters at the time of such offering. 

  
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 6. Withholding. 

No Shares will be issued pursuant to the exercise of this option unless and until the Participant pays to the Company, or makes provision
satisfactory to the Company for payment of, any federal, state or local withholding taxes required by law to be withheld in respect of this option. 
 7.
Nontransferability of Option. 
 This option may not be sold, assigned, transferred, pledged or otherwise encumbered by the
Participant, either voluntarily or by operation of law, except by will or the laws of descent and distribution, and, during the lifetime of the Participant, this option shall be exercisable only by the Participant. 

8. Provisions of the Plan. 
 This option
is subject to the provisions of the Plan, a copy of which is furnished to the Participant with this option. 
 IN WITNESS WHEREOF, the
Company has caused this option to be executed under its corporate seal by its duly authorized officer. This option shall take effect as a sealed instrument. 
  

									
		 		 	 CASA SYSTEMS, INC.

				
	Dated:                     	 		 	By:	 	 
		 		 		 	Name:	 	 
		 		 		 	Title:	 	 

  
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 PARTICIPANT’S ACCEPTANCE 

The undersigned hereby accepts the foregoing option and agrees to the terms and conditions thereof. The undersigned hereby acknowledges
receipt of a copy of the Company’s 2003 Stock Incentive Plan. 
  

			
	PARTICIPANT:
	
	 
	Address:	 	 
		 	 

  
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 Exhibit A 

NOTICE OF STOCK OPTION EXERCISE 

Date:                     1 
 Casa Systems, Inc. 

100 Old River Road, Suite 100 
 Andover, MA 01810 

Attention: Treasurer 
 Dear Sir or Madam: 

I am the holder of
                    2 Stock Option granted to me under the Casa Systems, Inc. (the
“Company”) 2003 Stock Incentive Plan on                     3 for the purchase
of                     4 shares of Common Stock of the Company at a purchase price of
$                    5 per share. 

I hereby exercise my option to purchase
                    6 shares of Common Stock (the “Shares”), for which I
have enclosed                     7 in the amount of
                    8. Please register my stock certificate as follows: 

 

					
	Name(s):	 	 	 	99
		 	 	 	
	Address:	 	 	 	
	Tax I.D. #:	 	 	 	1010

  

	1 	Enter the date of exercise. 

	2 	Enter either “an Incentive” or “a Nonstatutory”. 

	3 	Enter the date of grant. 

	4 	Enter the total number of shares of Common Stock for which the option was granted. 

	5 	Enter the option exercise price per share of Common Stock. 

	6 	Enter the number of shares of Common Stock to be purchased upon exercise of all or part of the option. 

	7 	Enter “cash”, “personal check” or if permitted by the option or Plan, “stock certificates No. XXXX and XXXX”. 

	8 	Enter the dollar amount (price per share of Common Stock times the number of shares of Common Stock to be purchased), or the number of shares tendered. Fair market value of shares tendered, together with cash or check,
must cover the purchase price of the shares issued upon exercise. 

	9 	Enter name(s) to appear on stock certificate: (a) Your name only; (b) Your name and other name (i.e., John Doe and Jane Doe, Joint Tenants With Right of Survivorship); or (c) In the case of a Nonstatutory option only, a
Child’s name, with you as custodian (i.e., Jane Doe, Custodian for Tommy Doe). Note: There may be income and/or gift tax consequences of registering shares in a Child’s name. 

	10 	Social Security Number of Holder(s). 

 I represent, warrant and covenant as follows: 

9. I am purchasing the Shares for my own account for investment only, and not with a view to, or for sale in connection with, any distribution of the Shares
in violation of the Securities Act of 1933 (the “Securities Act”), or any rule or regulation under the Securities Act. 
 10. I have had such
opportunity as I have deemed adequate to obtain from representatives of the Company such information as is necessary to permit me to evaluate the merits and risks of my investment in the Company. 

11. I have sufficient experience in business, financial and investment matters to be able to evaluate the risks involved in the purchase of the Shares and to
make an informed investment decision with respect to such purchase. 
 12. I can afford a complete loss of the value of the Shares and am able to bear the
economic risk of holding such Shares for an indefinite period. 
 13. I understand that (i) the Shares have not been registered under the Securities Act and
are “restricted securities” within the meaning of Rule 144 under the Securities Act, (ii) the Shares cannot be sold, transferred or otherwise disposed of unless they are subsequently registered under the Securities Act or an exemption from
registration is then available; (iii) in any event, the exemption from registration under Rule 144 will not be available for at least one year and even then will not be available unless a public market then exists for the Common Stock, adequate
information concerning the Company is then available to the public, and other terms and conditions of Rule 144 are complied with; and (iv) there is now no registration statement on file with the Securities and Exchange Commission with respect to any
stock of the Company and the Company has no obligation or current intention to register the Shares under the Securities Act. 
  

	
	Very truly yours,
	
	 
	(Signature)EX-10.5

 Exhibit 10.5 

CASA SYSTEMS, INC. 
 Restricted
Stock Agreement 
 Granted Under 2003 Stock Incentive Plan 

AGREEMENT made this              day of
                    , 200    , between Casa Systems, Inc., a Delaware corporation (the “Company”), and
                                         
(the “Participant”). 
 For valuable consideration, receipt of which is acknowledged, the parties hereto agree as follows: 

1. Purchase of Shares. 

The Company shall issue and sell to the Participant, and the Participant shall purchase from the Company, subject to the terms and conditions
set forth in this Agreement and in the Company’s 2003 Stock Incentive Plan (the “Plan”),              shares (the “Shares”) of common stock, $.001 par value,
of the Company (“Common Stock”), at a purchase price of $         per share. The aggregate purchase price for the Shares shall be paid by the Participant by check payable to the order of
the Company or such other method as may be acceptable to the Company. Upon receipt by the Company of payment for the Shares, the Company shall issue to the Participant one or more certificates in the name of the Participant for that number of
Shares purchased by the Participant. The Participant agrees that the Shares shall be subject to the purchase options set forth in Sections 2 and 5 of this Agreement and the restrictions on transfer set forth in Section 4 of this
Agreement. 
 2. Purchase Option. 

(a) In the event that the Participant ceases to be employed by the Company for any reason or no reason, with or without cause, prior
to                     , 200     [date that is four years after the vesting commencement date],
the Company shall have the right and option (the “Purchase Option”) to purchase from the Participant, for a sum of $         per share (the “Option Price”), some or all of the
Unvested Shares (as defined below). 
 “Unvested Shares” means the total number of Shares multiplied by the Applicable Percentage
at the time the Purchase Option becomes exercisable by the Company. The “Applicable Percentage” shall be (i) 100% during the 12-month period ending
                    , 200     [date that is one year after vesting commencement date], (ii) 75%
less 2.0833% for each one month of employment completed by the Participant with the Company from and after                     ,
200     [date that is one year after vesting commencement date], and (iii) zero on or after
                    , 200     [date that is four years after vesting commencement date]. 

(b) For purposes of this Agreement, employment with the Company shall include employment with a parent or subsidiary of the Company and
services to the Company as an advisor, consultant or member of the Board of Directors. 

 3. Exercise of Purchase Option and Closing. 

(a) The Company may exercise the Purchase Option by delivering or mailing to the Participant (or his estate), within 60 days after the
termination of the employment of the Participant with the Company, a written notice of exercise of the Purchase Option. Such notice shall specify the number of Shares to be purchased. If and to the extent the Purchase Option is not so
exercised by the giving of such a notice within such 60-day period, the Purchase Option shall automatically expire and terminate effective upon the expiration of such 60-day period. 

(b) Within 10 days after delivery to the Participant of the Company’s notice of the exercise of the Purchase Option pursuant to
subsection (a) above, the Participant (or his estate) shall, pursuant to the provisions of the Joint Escrow Instructions referred to in Section 7 below, tender to the Company at its principal offices the certificate or certificates
representing the Shares which the Company has elected to purchase in accordance with the terms of this Agreement, duly endorsed in blank or with duly endorsed stock powers attached thereto, all in form suitable for the transfer of such Shares to the
Company. Promptly following its receipt of such certificate or certificates, the Company shall pay to the Participant the aggregate Option Price for such Shares (provided that any delay in making such payment shall not invalidate the
Company’s exercise of the Purchase Option with respect to such Shares). 
 (c) After the time at which any Shares are required to be
delivered to the Company for transfer to the Company pursuant to subsection (b) above, the Company shall not pay any dividend to the Participant on account of such Shares or permit the Participant to exercise any of the privileges or rights of a
stockholder with respect to such Shares, but shall, in so far as permitted by law, treat the Company as the owner of such Shares. 
 (d) The
Option Price may be payable, at the option of the Company, in cancellation of all or a portion of any outstanding indebtedness of the Participant to the Company or in cash (by check) or both. 

(e) The Company shall not purchase any fraction of a Share upon exercise of the Purchase Option, and any fraction of a Share resulting from a
computation made pursuant to Section 2 of this Agreement shall be rounded to the nearest whole Share (with any one-half Share being rounded upward). 

(f) The Company may assign its Purchase Option to one or more persons or entities. 

4. Restrictions on Transfer. 

(a) The Participant shall not sell, assign, transfer, pledge, hypothecate or otherwise dispose of, by operation of law or otherwise
(collectively “transfer”) any Shares, or any interest therein, that are subject to the Purchase Option, except that the Participant may transfer such Shares (i) to or for the benefit of any spouse or any of his or his spouse’s
children, parents, uncles, aunts, siblings, grandchildren and any other relatives approved by the Board of Directors (collectively, “Approved Relatives”) or to a trust or similar entity established solely for the benefit of the Participant
and/or Approved Relatives, provided that such Shares shall remain subject to this Agreement (including without limitation the restrictions on transfer set forth in 

 
this Section 4, the Purchase Option and the right of first refusal set forth in Section 5) and such permitted transferee shall, as a condition to such transfer, deliver to the Company a written
instrument confirming that such transferee shall be bound by all of the terms and conditions of this Agreement or (ii) as part of the sale of all or substantially all of the shares of capital stock, assets or business of the Company, by merger,
consolidation, sale of assets or otherwise, provided that, in accordance with the Plan, the securities or other property received by the Participant in connection with such transaction shall remain subject to this Agreement. 

(b) The Participant shall not transfer any Shares, or any interest therein, that are no longer subject to the Purchase Option, except in
accordance with Section 5 below. 
 (c) The Participant shall not transfer any Shares, or any interest therein, whether or not such Shares
are subject to the Purchase Option, to any person or entity that is a competitor of the Company, as determined by the Board of Directors of the Company in its sole discretion, unless such transfer is made in connection with the sale of all or
substantially all of the capital stock, assets or business of the Company, by merger, consolidation, sale of assets or otherwise. 
 5.
Right of First Refusal. 
 (a) If the Participant proposes to transfer any Shares that are no longer subject to the Purchase Option
(either because they are no longer Unvested Shares or because the Purchase Option expired unexercised), then the Participant shall first give written notice of the proposed transfer (the “Transfer Notice”) to the Company. The Transfer
Notice shall name the proposed transferee and state the number of such Shares the Participant proposes to transfer (the “Offered Shares”), the price per share and all other material terms and conditions of the transfer. 

(b) For 60 days following its receipt of such Transfer Notice, the Company shall have the option to purchase some or all of the Offered Shares
at the price and upon the terms set forth in the Transfer Notice. In the event the Company elects to purchase any Offered Shares (the Offered Shares to be purchased by the Company hereunder are referred to as the “Purchased Shares”),
it shall give written notice of such election to the Participant within such 60-day period. Within 10 days his receipt of such notice, the Participant shall tender to the Company at its principal offices the certificate or certificates
representing the Purchased Shares, duly endorsed in blank by the Participant or with duly endorsed stock powers attached thereto, all in form suitable for transfer of the Purchased Shares to the Company. Promptly following receipt of such
certificate or certificates, the Company shall deliver or mail to the Participant a check in payment of the purchase price for the Purchased Shares; provided that if the terms of payment set forth in the Transfer Notice were other
than cash against delivery, the Company may pay for the Purchased Shares on the same terms and conditions as were set forth in the Transfer Notice; and provided further that any delay in making such payment shall not invalidate the
Company’s exercise of its option to purchase the Purchased Shares. 
 (c) If the Company does not elect to acquire all of the Offered
Shares, the Participant may, within the 30-day period following the expiration of the option granted to the Company under subsection (b) above, transfer the Offered Shares (other than the Purchased Shares) to
the proposed transferee, provided that such transfer shall not be on terms and 

 
conditions more favorable to the transferee than those contained in the Transfer Notice. Notwithstanding any of the above, all Offered Shares transferred to a third party pursuant to this
Section 5 shall remain subject to this Agreement (including without limitation the restrictions on transfer set forth in Section 4 and the right of first refusal set forth in this Section 5) and such transferee shall, as a condition to such
transfer, deliver to the Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of this Agreement. 

(d)    After the time at which the Purchased Shares are required to be delivered to the Company for transfer to the
Company pursuant to subsection (b) above, the Company shall not pay any dividend to the Participant on account of such Purchased Shares or permit the Participant to exercise any of the privileges or rights of a stockholder with respect to such
Purchased Shares, but shall, in so far as permitted by law, treat the Company as the owner of such Purchased Shares. 

(e)    The following transactions shall be exempt from the provisions of this Section 5: 

(1)    a transfer of Shares to or for the benefit of any Approved Relatives, or to a trust or similar entity established
solely for the benefit of the Participant and/or Approved Relatives; 
 (2)    any transfer pursuant to an effective
registration statement filed by the Company under the Securities Act of 1933, as amended (the “Securities Act”); and 

(3)    the sale of all or substantially all of the shares of capital stock of the Company (including pursuant to a merger
or consolidation); 
 (4)    provided, however, that in the case of a transfer pursuant to clause (1) above, such
Shares shall remain subject to this Agreement (including without limitation the restrictions on transfer set forth in Section 4 and the right of first refusal set forth in this Section 5) and such transferee shall, as a condition to such transfer,
deliver to the Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of this Agreement. 

(f)    The Company may assign its rights to purchase Offered Shares in any particular transaction under this Section 5 to
one or more persons or entities. 
 (g)    The provisions of this Section 5 shall terminate upon the earlier of the
following events: 
 (1)    the closing of the sale of shares of Common Stock in an underwritten public offering
pursuant to an effective registration statement filed by the Company under the Securities Act; or 
 (2)    the sale of
all or substantially all of the capital stock (other than the sale of capital stock to one or more venture capitalists or other institutional investors pursuant to an equity financing (including a debt financing that is convertible into equity) of
the Company 

 
approved by a majority of the Board of Directors of the Company), assets or business of the Company, by merger, consolidation, sale of assets or otherwise (other than a merger or consolidation in
which all or substantially all of the individuals and entities who were beneficial owners of the Common Stock immediately prior to such transaction beneficially own, directly or indirectly, more than 50% of the outstanding securities entitled to
vote generally in the election of directors of the resulting, surviving or acquiring corporation in such transaction). 
 (h) The Company
shall not be required (i) to transfer on its books any of the Shares which shall have been sold or transferred in violation of any of the provisions set forth in this Agreement, or (ii) to treat as owner of such Shares or to pay dividends
to any transferee to whom any such Shares shall have been so sold or transferred. 
 6. Agreement in Connection with Public Offering.

 The Participant agrees, in connection with the initial underwritten public offering of the Company’s securities pursuant to a
registration statement under the Securities Act, (i) not to sell, make short sale of, loan, grant any options for the purchase of, or otherwise dispose of any shares of Common Stock held by the Participant (other than those shares included in the
offering) without the prior written consent of the Company or the underwriters managing such initial underwritten public offering of the Company’s securities for a period of 180 days from the effective date of such registration statement, and
(ii) to execute any agreement reflecting clause (i) above as may be requested by the Company or the managing underwriters at the time of such offering. 

7. Escrow. 
 The
Participant shall, upon the execution of this Agreement, execute Joint Escrow Instructions in the form attached to this Agreement as Exhibit A. The Joint Escrow Instructions shall be delivered to the Secretary of the Company, as escrow
agent thereunder. The Participant shall deliver to such escrow agent a stock assignment duly endorsed in blank, in the form attached to this Agreement as Exhibit B, and hereby instructs the Company to deliver to such escrow agent, on
behalf of the Participant, the certificate(s) evidencing the Shares issued hereunder. Such materials shall be held by such escrow agent pursuant to the terms of such Joint Escrow Instructions. 

8. Restrictive Legends. 

All certificates representing Shares shall have affixed thereto legends in substantially the following form, in addition to any other legends
that may be required under federal or state securities laws: 
 “The shares of stock represented by this certificate are subject to
restrictions on transfer and an option to purchase set forth in a certain Restricted Stock Agreement between the corporation and the registered owner of these shares (or his predecessor in interest), and such Agreement is available for inspection
without charge at the office of the Secretary of the corporation.” 

 “The shares represented by this certificate have not been registered under the Securities
Act of 1933, as amended, and may not be sold, transferred or otherwise disposed of in the absence of an effective registration statement under such Act or an opinion of counsel satisfactory to the corporation to the effect that such registration is
not required.” 
 9. Provisions of the Plan. 

(a) This Agreement is subject to the provisions of the Plan, a copy of which is furnished to the Participant with this Agreement. 

(b) As provided in the Plan, upon the occurrence of a Reorganization Event (as defined in the Plan), the repurchase and other rights of the
Company hereunder shall inure to the benefit of the Company’s successor and shall apply to the cash, securities or other property which the Shares were converted into or exchanged for pursuant to such Reorganization Event in the same manner and
to the same extent as they applied to the Shares under this Agreement. If, in connection with a Reorganization Event, a portion of the cash, securities and/or other property received upon the conversion or exchange of the Shares is to be placed
into escrow to secure indemnification or similar obligations, the mix between the vested and unvested portion of such cash, securities and/or other property that is placed into escrow shall be the same as the mix between the vested and unvested
portion of such cash, securities and/or other property that is not subject to escrow. 
 10. Investment Representations. 

The Participant represents, warrants and covenants as follows: 

(a) The Participant is purchasing the Shares for his own account for investment only, and not with a view to, or for sale in connection with,
any distribution of the Shares in violation of the Securities Act, or any rule or regulation under the Securities Act. 
 (b) The
Participant has had such opportunity as he has deemed adequate to obtain from representatives of the Company such information as is necessary to permit him to evaluate the merits and risks of his investment in the Company. 

(c) The Participant has sufficient experience in business, financial and investment matters to be able to evaluate the risks involved in the
purchase of the Shares and to make an informed investment decision with respect to such purchase. 
 (d) The Participant can afford a
complete loss of the value of the Shares and is able to bear the economic risk of holding such Shares for an indefinite period. 
 (e) The
Participant understands that (i) the Shares have not been registered under the Securities Act and are “restricted securities” within the meaning of Rule 144 under the Securities Act; (ii) the Shares cannot be sold,
transferred or otherwise disposed of unless they are subsequently registered under the Securities Act or an exemption from registration is then available; (iii) in any event, the exemption from registration under Rule 144 will not be
available 

 
for at least one year and even then will not be available unless a public market then exists for the Common Stock, adequate information concerning the Company is then available to the public, and
other terms and conditions of Rule 144 are complied with; and (iv) there is now no registration statement on file with the Securities and Exchange Commission with respect to any stock of the Company and the Company has no obligation or
current intention to register the Shares under the Securities Act. 
 11. Withholding Taxes; Section 83(b) Election. 

(a) The Participant acknowledges and agrees that the Company has the right to deduct from payments of any kind otherwise due to the
Participant any federal, state or local taxes of any kind required by law to be withheld with respect to the purchase of the Shares by the Participant or the lapse of the Purchase Option. 

(b) The Participant has reviewed with the Participant’s own tax advisors the federal, state, local and foreign tax consequences of this
investment and the transactions contemplated by this Agreement. The Participant is relying solely on such advisors and not on any statements or representations of the Company or any of its agents. The Participant understands that the
Participant (and not the Company) shall be responsible for the Participant’s own tax liability that may arise as a result of this investment or the transactions contemplated by this Agreement. The Participant understands that it may be
beneficial in many circumstances to elect to be taxed at the time the Shares are purchased rather than when and as the Company’s Purchase Option expires by filing an election under Section 83(b) of the Code with the I.R.S. within 30 days from
the date of purchase. 
 THE PARTICIPANT ACKNOWLEDGES THAT IT IS THE PARTICIPANT’S SOLE RESPONSIBILITY AND NOT THE COMPANY’S TO
FILE TIMELY THE ELECTION UNDER SECTION 83(b), EVEN IF THE PARTICIPANT REQUESTS THE COMPANY OR ITS REPRESENTATIVES TO MAKE THIS FILING ON THE PARTICIPANT’S BEHALF. 

12. Miscellaneous. 
 (a)
No Rights to Employment. The Participant acknowledges and agrees that the vesting of the Shares pursuant to Section 2 hereof is earned only by continuing service as an employee at the will of the Company (not through the act of being
hired or purchasing shares hereunder). The Participant further acknowledges and agrees that the transactions contemplated hereunder and the vesting schedule set forth herein do not constitute an express or implied promise of continued
engagement as an employee or consultant for the vesting period, for any period, or at all. 
 (b) Severability. The invalidity
or unenforceability of any provision of this Agreement shall not affect the validity or enforceability of any other provision of this Agreement, and each other provision of this Agreement shall be severable and enforceable to the extent permitted by
law.

 (c) Waiver. Any provision for the benefit of the Company contained in this Agreement
may be waived, either generally or in any particular instance, by the Board of Directors of the Company. 
 (d) Binding
Effect. This Agreement shall be binding upon and inure to the benefit of the Company and the Participant and their respective heirs, executors, administrators, legal representatives, successors and assigns, subject to the restrictions on
transfer set forth in Sections 4 and 5 of this Agreement. 
 (e) Notice. All notices required or permitted hereunder shall
be in writing and deemed effectively given upon personal delivery or five days after deposit in the United States Post Office, by registered or certified mail, postage prepaid, if to the Participant, to the address set forth below or at the address
shown on the records of the Company, and if to the Company, to the Company’s principal executive offices, attention of the Corporate Secretary. 

(f) Pronouns. Whenever the context may require, any pronouns used in this Agreement shall include the corresponding masculine,
feminine or neuter forms, and the singular form of nouns and pronouns shall include the plural, and vice versa. 
 (g) Entire
Agreement. This Agreement and the Plan constitute the entire agreement between the parties, and supersedes all prior agreements and understandings, relating to the subject matter of this Agreement. 

(h) Amendment. This Agreement may be amended or modified only by a written instrument executed by both the Company and the
Participant. 
 (i) Governing Law. This Agreement shall be construed, interpreted and enforced in accordance with the internal
laws of the State of Delaware without regard to any applicable conflicts of laws. 
 (j) Participant’s Acknowledgments. The
Participant acknowledges that he or she: (i) has read this Agreement; (ii) has been represented in the preparation, negotiation, and execution of this Agreement by legal counsel of the Participant’s own choice or has voluntarily declined to
seek such counsel; (iii) understands the terms and consequences of this Agreement; (iv) is fully aware of the legal and binding effect of this Agreement; and (v) understands that the law firm of Hale and Dorr LLP, is acting as counsel to the Company
in connection with the transactions contemplated by the Agreement, and is not acting as counsel for the Participant. 

 IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the day and year first
above written. 
  

			
	CASA SYSTEMS, INC.
		
	By:	 	 
	Name:	 	 
	Title:	 	 
	Address:	 	 
		 	 
	
	 
	
	 
	Name of Participant
		
	Address:	 	 
		 	 

 Exhibit A 

CASA SYSTEMS, INC. 
 Joint
Escrow Instructions 

                    ,
200     
 Casa Systems, Inc. 
 100
Old River Road, Suite 100 
 Andover, MA 01810 

Attention: Secretary 
 Dear Sir: 

As Escrow Agent for Casa Systems, Inc., a Delaware corporation, and its successors in interest under the Restricted Stock Agreement (the
“Agreement”) of even date herewith, to which a copy of these Joint Escrow Instructions is attached (the “Company”), and the undersigned person (“Holder”), you are hereby authorized and directed to hold the documents
delivered to you pursuant to the terms of the Agreement in accordance with the following instructions: 
 1. Appointment. Holder
irrevocably authorizes the Company to deposit with you any certificates evidencing Shares (as defined in the Agreement) to be held by you hereunder and any additions and substitutions to said Shares. For purposes of these Joint Escrow
Instructions, “Shares” shall be deemed to include any additional or substitute property. Holder does hereby irrevocably constitute and appoint you as his attorney-in-fact and agent for the term of this escrow to execute with respect
to such Shares all documents necessary or appropriate to make such Shares negotiable and to complete any transaction herein contemplated. Subject to the provisions of this paragraph 1 and the terms of the Agreement, Holder shall exercise
all rights and privileges of a stockholder of the Company while the Shares are held by you. 
 2. Closing of Purchase. 

(a) Upon any purchase by the Company of the Shares pursuant to the Agreement, the Company shall give to Holder and you a written notice
specifying the purchase price for the Shares, as determined pursuant to the Agreement, and the time for a closing hereunder (the “Closing”) at the principal office of the Company. Holder and the Company hereby irrevocably authorize
and direct you to close the transaction contemplated by such notice in accordance with the terms of said notice. 
 (b) At the Closing, you
are directed (a) to date the stock assignment form or forms necessary for the transfer of the Shares, (b) to fill in on such form or forms the number of Shares being transferred, and (c) to deliver same, together with the certificate
or certificates evidencing the Shares to be transferred, to the Company against the simultaneous delivery to you of the purchase price for the Shares being purchased pursuant to the Agreement. 

 3. Withdrawal. The Holder shall have the right to withdraw from this escrow any
Shares as to which the Purchase Option (as defined in the Agreement) has terminated or expired. 
 4. Duties of Escrow Agent. 

(a) Your duties hereunder may be altered, amended, modified or revoked only by a writing signed by all of the parties hereto. 

(b) You shall be obligated only for the performance of such duties as are specifically set forth herein and may rely and shall be protected in
relying or refraining from acting on any instrument reasonably believed by you to be genuine and to have been signed or presented by the proper party or parties. You shall not be personally liable for any act you may do or omit to do hereunder
as Escrow Agent or as attorney-in-fact of Holder while acting in good faith and in the exercise of your own good judgment, and any act done or omitted by you pursuant to the advice of your own attorneys shall be conclusive evidence of such good
faith. 
 (c) You are hereby expressly authorized to disregard any and all warnings given by any of the parties hereto or by any other
person or Company, excepting only orders or process of courts of law, and are hereby expressly authorized to comply with and obey orders, judgments or decrees of any court. In case you obey or comply with any such order, judgment or decree of
any court, you shall not be liable to any of the parties hereto or to any other person, firm or Company by reason of such compliance, notwithstanding any such order, judgment or decree being subsequently reversed, modified, annulled, set aside,
vacated or found to have been entered without jurisdiction. 
 (d) You shall not be liable in any respect on account of the identity,
authority or rights of the parties executing or delivering or purporting to execute or deliver the Agreement or any documents or papers deposited or called for hereunder. 

(e) You shall be entitled to employ such legal counsel and other experts as you may deem necessary properly to advise you in connection with
your obligations hereunder and may rely upon the advice of such counsel. 
 (f) Your rights and responsibilities as Escrow Agent hereunder
shall terminate if (i) you cease to be Secretary of the Company or (ii) you resign by written notice to each party. In the event of a termination under clause (i), your successor as Secretary shall become Escrow Agent hereunder;
in the event of a termination under clause (ii), the Company shall appoint a successor Escrow Agent hereunder. 
 (g) If you reasonably
require other or further instruments in connection with these Joint Escrow Instructions or obligations in respect hereto, the necessary parties hereto shall join in furnishing such instruments. 

(h) It is understood and agreed that should any dispute arise with respect to the delivery and/or ownership or right of possession of the
securities held by you hereunder, you are 

 
authorized and directed to retain in your possession without liability to anyone all or any part of said securities until such dispute shall have been settled either by mutual written agreement
of the parties concerned or by a final order, decree or judgment of a court of competent jurisdiction after the time for appeal has expired and no appeal has been perfected, but you shall be under no duty whatsoever to institute or defend any such
proceedings. 
 (i) These Joint Escrow Instructions set forth your sole duties with respect to any and all matters pertinent hereto and no
implied duties or obligations shall be read into these Joint Escrow Instructions against you. 
 (j) The Company shall indemnify you and
hold you harmless against any and all damages, losses, liabilities, costs, and expenses, including attorneys’ fees and disbursements, for anything done or omitted to be done by you as Escrow Agent in connection with this Agreement or the
performance of your duties hereunder, except such as shall result from your gross negligence or willful misconduct. 
 5.
Notice. Any notice required or permitted hereunder shall be given in writing and shall be deemed effectively given upon personal delivery or upon deposit in the United States Post Office, by registered or certified mail with postage and
fees prepaid, addressed to each of the other parties thereunto entitled at the following addresses, or at such other addresses as a party may designate by ten days’ advance written notice to each of the other parties hereto. 

 

			
	COMPANY:	  	Casa Systems, Inc.
		  	 100 Old River Road, Suite 100
 Andover,
MA 01810

		
	HOLDER:	  	Notices to Holder shall be sent to the address set forth below Holder’s signature below.
	ESCROW AGENT:	  	Casa Systems, Inc.
		  	100 Old River Road, Suite 100
Andover, MA 01810
		  	Attn: Secretary

 6. Miscellaneous. 

(a) By signing these Joint Escrow Instructions, you become a party hereto only for the purpose of said Joint Escrow Instructions, and you do
not become a party to the Agreement. 

 (b) This instrument shall be binding upon and inure to the benefit of the parties hereto and
their respective successors and permitted assigns. 
  

			
	Very truly yours,
	
	CASA SYSTEMS, INC.
		
	By:	 	 
	Name:	 	 
	Title:	 	 
		
	HOLDER:	 	
	
	   

	(Signature)
	
	   

	Print Name
		
	Address:	 	 
		 	 
		
	Date Signed:	 	 

  

	
	ESCROW AGENT:
	
	   

	Jerry Guo
	Secretary
	Casa Systems, Inc.
	100 Old River Road, Suite 100
	Andover, MA 01810

			
		  	Exhibit B
		
		  	(STOCK ASSIGNMENT SEPARATE FROM CERTIFICATE)

 FOR VALUE RECEIVED, I hereby sell, assign and transfer unto
                    
(                    ) shares of Common Stock, $.001 par value per share, of Casa Systems, Inc. (the “Corporation”) standing in my
name on the books of said Corporation represented by Certificate(s) Number                      herewith, and do hereby irrevocably constitute
and appoint                     
                     attorney to transfer the said stock on the books of the within named Corporation with full power of substitution in the
premises. 
  

							
		 		 	Dated:	 	 
				
	IN PRESENCE OF	 		 		 	 
				
		 		 		 	 

 NOTICE: The signature(s) to this assignment must correspond with the name as written upon the face of the
certificate, in every particular, without alteration, enlargement, or any change whatever and must be guaranteed by a commercial bank, trust company or member firm of the Boston, New York or Midwest Stock Exchange.

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