SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

Schedule 13G
(Rule 13d-102)
INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1 (b), (c) AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 (b)
(Amendment No. 1)*

Zendesk, Inc.
(Name of Issuer)
Common Stock, par value $0.001
(Title of Class of Securities)
98936J101
(CUSIP Number)
December 31, 2015
(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
¨ Rule 13d-1(b)
¨ Rule 13d-1(c)
x Rule 13d-1(d)
 
*	The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.	
The information required on 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).
(Continued on following pages)
Page 1 of 9

 

			
CUSIP No: 98936J101	  		
	  	Page 2 of 9	

							
  1 	 	NAME OF REPORTING
SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Matrix Partners IX, L.P.	
  2	 	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
(a)   ¨         (b)   x 1
 	
  3	 	SEC USE ONLY
 	
  4	 	CITIZENSHIP OR PLACE OF ORGANIZATION
 
Delaware, USA	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH	  	5 	  	SOLE VOTING POWER
 
1,554,469 2	
	  	6	  	SHARED VOTING POWER
 	
	  	7	  	SOLE DISPOSITIVE POWER
 
1,554,469 2	
	  	8	  	SHARED DISPOSITIVE POWER
 	
  9	 	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 
1,554,469 2	
10	 	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
 
¨	
11	 	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
 
1.8 3 %	
12	 	TYPE OF REPORTING PERSON*
 
PN	

1  	This Schedule 13G is filed by Matrix Partners IX, L.P. (“Matrix IX”); Matrix IX Management Co., L.L.C. (“Matrix IX MC”), the general partner of Matrix IX; and Dana Stalder (“Mr. Stalder”), Managing Member of Matrix IX MC (collectively, the “Reporting Persons”). The Reporting Persons expressly disclaim status as a “group” for purposes of this Schedule 13G.	
2  	Represents 1,554,469 shares held by Matrix IX. Matrix IX MC is the general partner of Matrix IX, and Mr. Stalder is a managing member of Matrix IX MC. Mr. Stalder has sole voting and dispositive power with respect to the Matrix IX shares. The Reporting Persons disclaim beneficial ownership of the Matrix IX shares, except to the extent of their respective pecuniary interests therein.	
3  	This percentage is calculated based upon 88,697,514 shares of the Issuer’s common stock outstanding as of October 31, 2015.	

			
CUSIP No: 98936J101	  		
	  	Page 3 of 9	

  1 	 	NAME OF REPORTING
SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Matrix IX Management Co., L.L.C.	
  2	 	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
(a)   ¨         (b)   x 4
 	
  3	 	SEC USE ONLY
 	
  4	 	CITIZENSHIP OR PLACE OF ORGANIZATION
 
Delaware, USA	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH	  	5 	  	SOLE VOTING POWER
 
1,554,469 5	
	  	6	  	SHARED VOTING POWER
 	
	  	7	  	SOLE DISPOSITIVE POWER
 
1,554,469 5	
	  	8	  	SHARED DISPOSITIVE POWER
 	
  9	 	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 
1,554,469 5	
10	 	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
 
¨	
11	 	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
 
1.8 % 6	
12	 	TYPE OF REPORTING PERSON*
 
OO	

4  	This Schedule 13G is filed by the Reporting Persons. The Reporting Persons expressly disclaim status as a “group” for purposes of this Schedule 13G.	
5  	Represents 1,554,469 shares held by Matrix IX. Matrix IX MC is the general partner of Matrix IX, and Mr. Stalder is a managing member of Matrix IX MC. Mr. Stalder has sole voting and dispositive power with respect to the Matrix IX shares. The Reporting Persons disclaim beneficial ownership of the Matrix IX shares, except to the extent of their respective pecuniary interests therein.	
6  	This percentage is calculated based upon 88,697,514 shares of the Issuer’s common stock outstanding as of October 31, 2015.	

			
CUSIP No: 98936J101	  		
	  	Page 4 of 9	

  1 	 	NAME OF REPORTING
SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Dana Stalder	
  2	 	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
(a)   ¨         (b)   x 7
 	
  3	 	SEC USE ONLY
 	
  4	 	CITIZENSHIP OR PLACE OF ORGANIZATION
 
USA	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH	  	5 	  	SOLE VOTING POWER
 
1,632,112 8	
	  	6	  	SHARED VOTING POWER
 	
	  	7	  	SOLE DISPOSITIVE POWER
 
1,632,112 8	
	  	8	  	SHARED DISPOSITIVE POWER
 	
  9	 	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 
1,632,112 8	
10	 	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
 
¨	
11	 	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
 
1.8 % 9	
12	 	TYPE OF REPORTING PERSON*
 
IN	

7  	This Schedule 13G is filed by the Reporting Persons. The Reporting Persons expressly disclaim status as a “group” for purposes of this Schedule 13G.	
8  	Includes 1,554,469 shares held by Matrix IX and 2,672 shares held directly by Weston & Co. IX, LLC (“Weston IX”), as nominee for Vista Grande Trust (the “Trust”), a trust of which Mr. Stalder is the trustee and a beneficiary, and which is the beneficial owner of such shares (the “Weston Shares”) and 74,971 shares held by Vista Grande Trust (the “Trust Shares”). Matrix IX MC is the general partner of Matrix IX, and Mr. Stalder is a managing member of Matrix IX MC. Mr. Stalder has sole voting and dispositive power with respect to the Matrix IX Shares. The Trust has sole voting and dispositive power with respect to the Weston Shares and the Trust Shares. The Reporting Person disclaims beneficial ownership of the Matrix IX shares and the Trust Shares, except to the extent of his pecuniary interest therein.	
9  	This percentage is calculated based upon 88,697,514 shares of the Issuer’s common stock outstanding as of October 31, 2015.	

			
CUSIP No: 98936J101	  		
	  	Page 5 of 9	
 
ITEM 1(A).	NAME OF ISSUER	
Zendesk, Inc.
 
ITEM 1(B).	ADDRESS OF ISSUER’S PRINCIPAL EXECUTIVE OFFICES	
 
    	1019 Market Street	
San Francisco, CA 94103
 
ITEM 2(A).	NAME OF PERSONS FILING	
Matrix Partners IX, L.P. (“Matrix IX”)
Matrix IX Management Co., L.L.C. (“Matrix IX MC”)
Dana Stalder (“Mr. Stalder”)
 
ITEM 2(B).	ADDRESS OF PRINCIPAL OFFICE	
c/o Matrix Partners
101 Main Street, 17th Floor
Cambridge, MA 02142
 
ITEM 2(C).	CITIZENSHIP	
Matrix IX: Delaware limited partnership
Matrix IX MC: Delaware limited liability company
Mr. Stalder: USA
 
ITEM 2(D).	TITLE OF CLASS OF SECURITIES	
Common Stock, $0.001 par value per share (the “Common Stock”)
 
ITEM 2(E).	CUSIP NUMBER	
98936J101
 
ITEM 3.	Not Applicable	
 
ITEM 4.	OWNERSHIP	
Amount beneficially owned :
As of December 31, 2015: Matrix IX was the record holder of 1,554,469 shares of Common Stock (the “Matrix IX Shares”), Matrix IX MC was the record holder of 0 shares of Common Stock and Mr. Stalder was the record holder of 0 shares of Common Stock. Weston & Co. IX, LLC (“Weston IX”) was the holder of 2,672 shares of Common Stock as nominee of the Vista Grande Trust (the “Weston Shares”), of which Mr. Stalder is trustee and a beneficiary and which is the beneficial owner of such shares and 74,971 shares held by Vista Grande Trust (the “Trust Shares”).
Matrix IX MC, as the general partner of Matrix IX, has sole voting and dispositive power of the Matrix IX Shares. Mr. Stalder, as a managing member of Matrix IX MC, as General Partner of Matrix IX and as trustee of the Vista Grande Trust, has sole voting and dispositive power over the Matrix IX Shares, the Weston Shares and the Trust Shares.

			
CUSIP No: 98936J101	  		
	  	Page 6 of 9	
 
 	(a)	Percent of Class :	
Matrix IX: 1.8%
Matrix IX MC: 1.8%
Mr. Stalder: 1.8%
 
 	(b)	Number of shares as to which such person has :	
 
 	(i)	Sole power to vote or to direct the vote :	
Matrix IX: 1,554,469
Matrix IX MC: 1,554,469
Mr. Stalder: 1,632,112
 
 	(ii)	Shared power to vote or to direct the vote :	
Matrix IX: 0
Matrix IX MC: 0
Mr. Stalder: 0
 
 	(iii)	Sole power to dispose or to direct the disposition of :	
Matrix IX: 1,554,469
Matrix IX MC: 1,554,469
Mr. Stalder: 1,632,112
 
 	(iv)	Shared power to dispose or to direct the disposition of :	
Matrix IX: 0
Matrix IX MC: 0
Mr. Stalder: 0
 
ITEM 5.	OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS	
 
    	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 x .	
 
ITEM 6.	OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON .	
 
    	Not applicable.	
 
ITEM 7.	IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY	
 
    	Not applicable.	
 
ITEM 8.	IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP .	
 
    	Each of the Reporting Persons Expressly disclaims membership in a “Group” as defined in Rule 13d-1(b)(ii)(J).	
 
ITEM 9.	NOTICE OF DISSOLUTION OF GROUP .	
Not applicable.

			
CUSIP No: 98936J101	  		
	  	Page 7 of 9	
 
ITEM 10.	CERTIFICATION .	
Not applicable. This Schedule 13G is not filed pursuant to Rule 13d-1(b) or Rule 13d-1(c).

			
CUSIP No: 98936J101	  		
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SIGNATURES
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: February 8, 2016

Matrix Partners IX, L.P.	
		
By:	 	Matrix IX Management Co., L.L.C., its General Partner	
		
By:	 	        /s/ Dana Stalder	
	 	Dana Stalder, Authorized Member	
	
Matrix IX Management Co., L.L.C.	
		
By:	 	        /s/ Dana Stalder	
	 	Dana Stalder, Authorized Member	
		
	 	        /s/ Dana Stalder	
	 	Dana Stalder	

			
CUSIP No: 98936J101	  		
	  	Page 9 of 9	
 
EXHIBIT 99.1
JOINT FILING AGREEMENT
The undersigned, being duly authorized thereunder, hereby execute this agreement as an exhibit to this Schedule 13G to evidence the agreement of the below-named parties, in accordance with the rules promulgated pursuant to the Securities Exchange Act of 1934, to file this Schedule jointly on behalf of each such party.
This Agreement may be executed in any number of counterparts, each of which shall be deemed an original.
Date: February 8, 2016

Matrix Partners IX, L.P.	
		
By:	 	Matrix IX Management Co., L.L.C., its General Partner	
		
By:	 	        /s/ Dana Stalder	
	 	Dana Stalder, Authorized Member	
	
Matrix IX Management Co., L.L.C.	
		
By:	 	        /s/ Dana Stalder	
	 	Dana Stalder, Authorized Member	
		
	 	        /s/ Dana Stalder	
	 	Dana Stalder