Sec Form 4 Filing - Accel X LP @ Slack Technologies, Inc. - 2019-06-11

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Accel X LP 2. Issuer Name and Ticker or Trading Symbol Slack Technologies, Inc. [ WORK] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 500 UNIVERSITY AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 06/11/2019 (Street) PALO ALTO, CA94301 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Class A Common Stock 06/11/2019 C 17,146,080 A $ 0 ( 1 ) 17,146,080 D Class A Common Stock 06/11/2019 C 1,286,873 A $ 0 ( 1 ) 1,286,873 I By Accel X Strategic Partners L.P. ( 2 ) Class A Common Stock 06/11/2019 C 688,373 A $ 0 ( 1 ) 688,373 I By Accel Investors 2009 L.L.C ( 3 ) Class A Common Stock 06/11/2019 C 3,649,641 A $ 0 ( 1 ) 3,649,641 I By Accel XI L.P. ( 4 ) Class A Common Stock 06/11/2019 C 274,210 A $ 0 ( 1 ) 274,210 I By Accel XI Strategic Partners L.P. ( 5 ) Class A Common Stock 06/11/2019 C 387,596 A $ 0 ( 1 ) 387,596 I By Accel Investors 2013 L.L.C. ( 6 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Class B Common Stock ( 1 ) 06/11/2019 C 17,146,080 ( 1 ) ( 1 ) Class A Common Stock 17,146,080 $ 0 51,438,240 D Class B Common Stock ( 1 ) 06/11/2019 C 1,286,873 ( 1 ) ( 1 ) Class A Common Stock 1,286,873 $ 0 3,860,617 I By Accel X Strategic Partners L.P ( 2 ) Class B Common Stock ( 1 ) 06/11/2019 C 688,373 ( 1 ) ( 1 ) Class A Common Stock 688,373 $ 0 2,065,117 I By Accel Investors 2009 L.L.C ( 3 ) Class B Common Stock ( 1 ) 06/11/2019 C 3,649,641 ( 1 ) ( 1 ) Class A Common Stock 3,649,641 $ 0 10,948,923 I By Accel XI L.P. ( 4 ) Class B Common Stock ( 1 ) 06/11/2019 C 274,210 ( 1 ) ( 1 ) Class A Common Stock 274,210 $ 0 822,630 I By Accel XI Strategic Partners L.P. ( 5 ) Class B Common Stock ( 1 ) 06/11/2019 C 387,596 ( 1 ) ( 1 ) Class A Common Stock 387,596 $ 0 1,162,788 I By Accel Investors 2013 L.L.C. ( 6 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Accel X LP 500 UNIVERSITY AVENUE PALO ALTO, CA94301 X ACCEL X STRATEGIC PARTNERS LP 500 UNIVERSITY AVENUE PALO ALTO, CA94301 X Accel X Associates L.L.C. 500 UNIVERSITY AVENUE PALO ALTO, CA94301 X Accel Investors 2009 L.L.C. 500 UNIVERSITY AVE. PALO ALTO, CA94301 X Accel XI L.P. 500 UNIVERSITY AVE. PALO ALTO, CA94301 X Accel XI Strategic Partners L.P. 500 UNIVERSITY AVENUE PALO ALTO, CA94301 X Accel XI Associates L.L.C. 500 UNIVERSITY AVE PALO ALTO, CA94301 X Accel Investors 2013 L.L.C. 500 UNIVERSITY AVE. PALO ALTO, CA94301 X Signatures /s/ TRACY L. SEDLOCK. ATTORNEY IN FACT 06/12/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each share of Class B Common Stock is convertible without payment or consideration into one share of Class A Common Stock at the option of the holder and has no expiration date. ( 2 )These shares are held by Accel X Strategic Partners L.P. Accel X Associates L.L.C. is the general partner of each of the Accel X Entities. The managing members of Accel X Associates L.L.C. are Andrew G. Braccia, Kevin J. Efrusy, Sameer K. Gandhi, Ping Li, Tracy L. Sedlock, and Richard P. Wong. Accel X Associates L.L.C. has sole voting and dispositive power with regard to the shares held by the Accel X Entities, and its managing members share such powers. ( 3 )These shares are held by Accel Investors 2009 L.L.C. The managing member of Accel Investors 2009 L.L.C. are Andrew G. Braccia, Kevin J. Efrusy, Sameer K. Gandhi, Ping Li, Tracy L. Sedlock, and Richard P. Wong, all of whom share voting and dispositive power with regard to the shares held by Accel Investors 2009 L.L.C. ( 4 )These shares are held by Accel XI LP. Accel XI Associates L.L.C. is the general partner each of Accel XI L.P. and Accel XI Strategic Partners L.P. (together, the "Accel XI Entities"). The managing members of Accel XI Associates L.L.C. are Andrew G. Braccia, Sameer K. Gandhi, Ping Li, Tracy L. Sedlock, and Richard P. Wong. Accel XI Associates L.L.C. has sole voting and dispositive power with regard to the shares held by the Accel XI Entities, and its managing members share such powers. ( 5 )These shares are held by Accel XI Strategic Partners L.P. Accel XI Associates L.L.C. is the general partner of each of the Accel XI Entities. The managing members of Accel XI Associates L.L.C. are Andrew G. Braccia, Sameer K. Gandhi, Ping Li, Tracy L. Sedlock, and Richard P. Wong. Accel XI Associates L.L.C. has sole voting and dispositive power with regard to the shares held by the Accel XI Entities, and its managing members share such powers. ( 6 )These shares are held by Accel Investors 2013 L.L.C. The managing members of Accel Investors 2013 L.L.C. are Andrew G. Braccia, Sameer K. Gandhi, Ping Li, Tracy L. Sedlock, and Richard P. Wong, all of whom share voting and dispositive power with regard to the shares held by Accel Investors 2013 L.L.C.

Remarks: This Form 4 is the first of three Form 4s filed relating to the same event. Combined, the three reports report the holdings for the following reporting persons (the "Accel Reporting Persons"): Accel X L.P., Accel X Strategic Partners L.P., Accel X Associates L.L.C., Accel Investors 2009 L.L.C., Accel XI L.P., Accel XI Strategic Partners L.P., Accel XI Associates L.L.C., Accel Investors 2013 L.L.C., Accel Growth Fund III L.P., Accel Growth Fund III Strategic Partners L.P., Accel Growth Fund III Associates L.L.C., Accel Growth Fund Investors 2014 L.L.C., Accel Growth Fund IV L.P., Accel Growth Fund IV Strategic Partners L.P., Accel Growth Fund IV Associates L.L.C., Accel Growth Fund Investors 2016 L.L.C., Accel Leaders Fund L.P., Accel Leaders Fund Associates L.L.C. and Accel Leaders Fund Investors 2016 L.L.C. This Form 4 has been split into three filings because there are more than 10 Accel Reporting Persons in total, and the SEC's EDGAR filing system limits a single Form 4 to a maximum of 10 reporting persons. Each Form 4 is filed by designated filer Accel X L.P.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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