2019 Employee Stock Purchase Plan

The purpose of the Slack Technologies, Inc. 2019 Employee Stock Purchase Plan (the “Plan”) is to provide eligible employees of Slack Technologies, Inc. (the “Company”) and each Designated Company (as defined in Section 11) with opportunities to purchase shares of the Company’s Class A common stock, par value $0.0001 per share (the “Common Stock”). 9,000,000 shares of Common Stock in the aggregate have been approved and reserved for this purpose, plus on February 1, 2020 and each February 1 thereafter until the Plan terminates pursuant to Section 20, the number of shares of Common Stock reserved and available for issuance under the Plan shall be cumulatively increased by the lesser of (i) 6,000,000 shares of Common Stock, (ii) 1% percent of the number of shares of Common Stock and Class B common stock of the Company issued and outstanding on the immediately preceding January 31, or (iii) such lesser number of shares of Common Stock as determined by the Administrator (as defined in Section 1).

The Plan includes two components: a Code Section 423 Component (the “423 Component”) and a non-Code Section 423 Component (the “Non-423 Component”). It is intended for the 423 Component to constitute an “employee stock purchase plan” within the meaning of Section 423(b) of the U.S. Internal Revenue Code of 1986, as amended (the “Code”) and the 423 Component shall be interpreted in accordance with that intent. Under the Non-423 Component, which does not qualify as an “employee stock purchase plan” within the meaning of Section 423(b) of the Code, options will be granted pursuant to rules, procedures or sub-plans adopted by the Administrator designed to achieve tax, securities laws or other objectives for

eligible employees. Except as otherwise provided herein or by the Administrator, the Non-423 Component will operate and be administered in the same manner as the 423 Component.

Unless otherwise defined herein, capitalized terms in this Plan shall have the meaning ascribed to them in Section 11.

1.Administration. The Plan will be administered by the person or persons (the “Administrator”) appointed by the Company’s Board of Directors (the “Board”) for such purpose. The Administrator has authority at any time to: (i) adopt, alter and repeal such rules, guidelines and practices for the administration of the Plan and for its own acts and proceedings as it shall deem advisable; (ii) interpret the terms and provisions of the Plan; (iii) make all determinations it deems advisable for the administration of the Plan, including to accommodate the specific requirements of local laws, regulations and procedures for jurisdictions outside the United States; (iv) decide all disputes arising in connection with the Plan; and (v) otherwise supervise the administration of the Plan. All interpretations and decisions of the Administrator shall be binding on all persons, including the Company and the Participants. No member of the Board or individual exercising administrative authority with respect to the Plan shall be liable for any action or determination made in good faith with respect to the Plan or any option granted hereunder.

2.Offerings. The Company will make one or more offerings to eligible employees to purchase Common Stock under the Plan (“Offerings”) consisting of one or more Purchase Periods. Unless otherwise determined by the Administrator, the initial Offering will begin on the Listing Date and will end on October 9, 2019 (the “Initial Offering”) and consist of one Purchase Period. Thereafter, unless otherwise determined by the Administrator, an Offering will be six (6) months long, consist of one Purchase Period, and will begin on the first business day occurring

on or after each October 10th and April 10th and will end on the last business day occurring on or before the following April 9th and October 9th, respectively. The Administrator may, in its discretion, designate a different period for any Offering, provided that no Offering shall exceed twenty-seven (27) months in duration, and may also designate the number of Purchase Periods within each Offering.

3.Eligibility. Other than the Initial Offering, all individuals classified as employees on the payroll records of the Company and each Designated Company as of the first day of the applicable Offering (the “Offering Date”) that have submitted an enrollment form (in the manner described in Section 4(c)) within the time period required by the Administrator are eligible to participate in the applicable Offering under the Plan (provided that a Participant is not permitted to participate in multiple Offerings at the same time, unless otherwise determined by the Administrator). With respect to the Initial Offering, all individuals classified as employees on the payroll records of the Company and each Designated Company as of the first day of the Initial Offering are eligible to participate in the Initial Offering. Notwithstanding any other provision herein, individuals who are not contemporaneously classified as employees of the Company or a Designated Company for purposes of the Company’s or applicable Designated Company’s payroll system are not considered to be eligible employees of the Company or any Designated Subsidiary and shall not be eligible to participate in the Plan. In the event any such individuals are reclassified as employees of the Company or a Designated Company for any purpose, including, without limitation, common law or statutory employees, by any action of any third party, including, without limitation, any government agency, or as a result of any private lawsuit, action or administrative proceeding, such individuals shall, notwithstanding such reclassification, remain ineligible for participation. Notwithstanding the foregoing, the exclusive

means for individuals who are not contemporaneously classified as employees of the Company or a Designated Company on the Company’s or Designated Company’s payroll system to become eligible to participate in this Plan is through an amendment to this Plan, duly executed by the Company, which specifically renders such individuals eligible to participate herein.

4.Participation.

(a)Participants on Listing Date. Each eligible employee as of the Listing Date shall be deemed to be a Participant at such time. If an eligible employee is deemed to be a Participant pursuant to this Section 4(a), such individual shall be deemed not to have authorized payroll deductions and shall not purchase any Common Stock hereunder unless he or she thereafter authorizes payroll deductions by submitting an enrollment form (in the manner described in Section 4(c)) within 5 business days of the Listing Date, or such other deadline as is specified by the Administrator. If such a Participant does not authorize payroll deductions by submitting an enrollment form within 5 business days of the Listing Date, or such other deadline as is specified by the Administrator, that Participant will be deemed to have withdrawn from the Plan.

(b)Participants in Subsequent Offerings. An eligible employee who is not a Participant in any prior Offering may participate in a subsequent Offering by submitting an enrollment form (in the manner described in Section 4(c)) at least 15 business days before the Offering Date (or by such other deadline as shall be established by the Administrator for the Offering).

(c)Enrollment. The enrollment form (which may be in an electronic format or such other method as determined by the Company in accordance with the Company’s practices) may include, but is not limited to, the following information from the Participant: (a) s

tate a whole percentage to be deducted from an eligible employee’s Compensation per pay period, (b) authorize the purchase of Common Stock in each Offering in accordance with the terms of the Plan and (c) specify the exact name or names in which shares of Common Stock purchased for such individual are to be issued or registered pursuant to Section 10. An employee who does not enroll in accordance with these procedures will be deemed to have waived the right to participate. Unless a Participant files a new enrollment form or withdraws from the Plan, such Participant’s deductions and purchases will continue at the same percentage of Compensation for future Offerings, provided he or she remains eligible.

(d)Notwithstanding the foregoing, participation in the Plan will neither be permitted nor be denied contrary to the requirements of the Code.

5.Employee Contributions. Each eligible employee may authorize payroll deductions at a minimum of 1 percent up to a maximum of 15 percent of such employee’s Compensation for each pay period. The Company will maintain book accounts showing the amount of payroll deductions made by each Participant for each Purchase Period within an Offering. No interest will accrue or be paid on payroll deductions, except as may be required by applicable law. If payroll deductions for purposes of the Plan are prohibited or otherwise problematic under applicable law (as determined by the Administrator in its discretion), the Administrator may require Participants to contribute to the Plan by such other means as determined by the Administrator. Any reference to “payroll deductions” in this Section 5 (or in any other section of the Plan) will similarly cover contributions by other means made pursuant to this Section 5.

6.Deduction Changes. Except in the event of a Participant increasing his or her payroll deduction from 0 percent during the first Offering as specified in Section 4(a) or as may

be determined by the Administrator in advance of an Offering, a Participant may not increase his or her payroll deduction during any Offering and may decrease his or her payroll deduction one time during each Offering. However, during an Offering, a Participant may increase or decrease his or her payroll deduction with respect to the next Offering (subject to the limitations of Section 5) by filing a new enrollment form at least 15 business days before the next Offering Date (or by such other deadline as shall be established by the Administrator for the Offering). The Administrator may, in advance of any Offering, establish rules permitting a Participant to increase, decrease or terminate his or her payroll deduction during an Offering.

7.Withdrawal. A Participant may withdraw from participation in the Plan by delivering a written notice of withdrawal to the Company (in accordance with such procedures as may be specified by the Administrator). The Participant’s withdrawal will be effective as soon as practicable. Following a Participant’s withdrawal, the Company will promptly refund such individual’s entire account balance under the Plan to him or her (after payment for any Common Stock purchased before the effective date of withdrawal). Partial withdrawals are not permitted. Such an employee may not begin participation again during the remainder of the Offering, but may enroll in a subsequent Offering in accordance with Section 4.

8.Grant of Options. On each Offering Date, the Company will grant to each Participant in the Plan an option (“Option”) to purchase on the last day of the Purchase Period (an “Exercise Date”), at the Option Price hereinafter provided for, the lowest of (a) a number of shares of Common Stock determined by dividing such Participant’s accumulated payroll deductions on such Exercise Date by the lower of (i) 85 percent of the Fair Market Value of the Common Stock on the Offering Date, or (ii) 85 percent of the Fair Market Value of the Common Stock on the business day prior to Exercise Date, (b) 1,250 shares; or (c) such other lesser

maximum number of shares as shall have been established by the Administrator in advance of the Offering; provided, however, that such Option shall be subject to the limitations set forth below. Each Participant’s Option shall be exercisable only to the extent of such Participant’s accumulated payroll deductions on the Exercise Date. The purchase price for each share purchased under each Option (the “Option Price”) will be 85 percent of the Fair Market Value of the Common Stock on the Offering Date or the business day prior to the Exercise Date, whichever is less.

Notwithstanding the foregoing, no Participant may be granted an Option hereunder if such Participant, immediately after the Option was granted, would be treated as owning stock possessing 5 percent or more of the total combined voting power or value of all classes of stock of the Company or any Parent or Subsidiary. For purposes of the preceding sentence, the attribution rules of Section 424(d) of the Code shall apply in determining the stock ownership of a Participant, and all stock which the Participant has a contractual right to purchase shall be treated as stock owned by the Participant. In addition, no Participant may be granted an Option which permits his or her rights to purchase stock under the Plan, and any other employee stock purchase plan of the Company and its Parents and Subsidiaries, to accrue at a rate which exceeds $25,000 of the Fair Market Value of such stock (determined on the Option grant date or dates) for each calendar year in which the Option is outstanding at any time. The purpose of the limitation in the preceding sentence is to comply with Section 423(b)(8) of the Code and shall be applied taking Options into account in the order in which they were granted.

9.Exercise of Option and Purchase of Shares. Each employee who continues to be a Participant in the Plan on an Exercise Date shall be deemed to have exercised his or her Option on such date and shall acquire from the Company such number of whole shares of Common

Stock reserved for the purpose of the Plan as his or her accumulated payroll deductions on such date will purchase at the Option Price, subject to any other limitations contained in the Plan. Unless otherwise determined by the Administrator in advance of an Offering, any amount remaining in a Participant’s account at the end of a Purchase Period solely by reason of the inability to purchase a fractional share will be carried forward to the next Purchase Period or promptly refunded and, if such Exercise Date is the final Exercise Date of an Offering, will be carried forward to the next Offering or promptly refunded; any other balance remaining in a Participant’s account at the end of an Offering will be refunded to the Participant promptly.

To the extent permitted by applicable laws, if the Fair Market Value of the Common Stock on any Exercise Date in an Offering Period is lower than the Fair Market Value of the Common Stock on the Offering Date of such Offering Period, then all Participants in such Offering Period automatically will be withdrawn from such Offering Period immediately after the exercise of their option on such Exercise Date and will be automatically re-enrolled in the immediately following Offering Period as of the first day thereof.

10.Issuance of Certificates. To the extent applicable, certificates representing shares of Common Stock purchased under the Plan may be issued only in the name of the employee, in the name of the employee and another person of legal age as joint tenants with rights of survivorship (or similar ownership form, if permitted under applicable law), or in the name of a broker authorized by the employee to be his, her or their, nominee for such purpose.

11.Definitions.

The term “Affiliate” means any entity that, directly or indirectly through one or more intermediaries, controls, is controlled by or is under the common control with, the Company.

The term “Compensation” means a Participant’s total cash compensation, prior to salary reduction (such as pursuant to Sections 125, 132(f) or 401(k) of the Code), including base pay, overtime, commissions, and annual incentive or annual bonus awards, but excluding allowances and reimbursements for expenses such as relocation allowances or travel expenses, spot bonuses or other discretionary awards, income or gains related to Company stock options or other share-based awards, and similar items. The Administrator shall have the discretion to determine the application of this definition to Participants outside the United States.

The term “Designated Company” means any present or future Subsidiary or Affiliate that has been designated by the Administrator to participate in the Plan. The Administrator may so designate any Subsidiary or Affiliate, or revoke any such designation, at any time and from time to time, either before or after the Plan is approved by the stockholders, and may further designate such companies or Participants as participating in the 423 Component or the Non-423 Component. The Administrator may also determine which Affiliates or eligible employees may be excluded from participation in the Plan, to the extent consistent with Section 423 of the Code or as implemented under the Non-423 Component, and determine which Designated Company or Companies will participate in separate Offerings (to the extent that the Company makes separate Offerings). For purposes of the 423 Component, only the Company and its Subsidiaries may be Designated Companies; provided, however, that at any given time, a Subsidiary that is a Designated Company under the 423 Component will not be a Designated Company under the Non-423 Component.

The term “Fair Market Value of the Common Stock” on any given date means the fair market value of the Common Stock determined in good faith by the Administrator; provided, however, that if the Common Stock is admitted to quotation on The New York Stock Exchange

or another national securities exchange, the determination shall be made by reference to the closing price on such date. If there is no closing price for such date, the determination shall be made by reference to the last date preceding such date for which there is a closing price. Notwithstanding the foregoing, if the date for which the Fair Market Value of the Common Stock is determined is the Listing Date, the Fair Market Value of the Common Stock shall be the closing price on the Listing Date.

The term “Listing Date” means the date that the Common Stock is first traded on The New York Stock Exchange.

The term “Parent” means a “parent corporation” with respect to the Company, as defined in Section 424(e) of the Code.

The term “Participant” means an individual who is eligible as determined in Section 3 and who has complied with the provisions of Section 4.

The term “Purchase Period” means a period of time specified within an Offering beginning on the Offering Date or on the next day following an Exercise Date within an Offering and ending on an Exercise Date. An Offering may consist of one or more Purchase Periods.

The term “Registration Date” means the date the registration statement on Form S-1 that is filed by the Company is declared effective by the SEC.

The term “Subsidiary” means a “subsidiary corporation” with respect to the Company, as defined in Section 424(f) of the Code.

12.Rights on Termination or Transfer of Employment. If a Participant’s employment terminates for any reason before the Exercise Date for any Offering, no payroll deduction will be taken from any pay due and owing to the Participant and the balance in the Participant’s account will be paid to such Participant or, in the case of such Participant’s death, to the legal

representative of his or her estate or to his or her designated beneficiary (provided the Administrator has permitted designation of a beneficiary for purposes of the Plan), as if such Participant had withdrawn from the Plan under Section 7. An employee will be deemed to have terminated employment, for this purpose, if the corporation that employs him or her, having been a Designated Company, ceases to be a Subsidiary or Affiliate, or if the employee is transferred to any corporation other than the Company or a Designated Company. Unless otherwise determined by the Administrator, a Participant whose employment transfers between, or whose employment terminates with an immediate rehire (with no break in service) by, Designated Companies or a Designated Company and the Company will not be treated as having terminated employment for purposes of participating in the Plan or an Offering; provided, however, that if a Participant transfers from an Offering under the 423 Component to an Offering under the Non-423 Component, the exercise of the Participant’s Option will be qualified under the 423 Component only to the extent that such exercise complies with Section 423 of the Code. If a Participant transfers from an Offering under the Non-423 Component to an Offering under the 423 Component, the exercise of the Participant’s Option will remain non-qualified under the Non-423 Component. Further, an employee will not be deemed to have terminated employment for purposes of the Plan, if the employee is on an approved leave of absence where the employee’s right to reemployment is guaranteed either by a statute or by contract or under the policy pursuant to which the leave of absence was granted or if the Administrator otherwise provides in writing.

13.Special Rules and Sub-Plans. Notwithstanding anything herein to the contrary, the Administrator may adopt special rules or sub-plans applicable to the employees of a particular Designated Company, whenever the Administrator determines that such rules are

necessary or appropriate for the implementation of the Plan in a jurisdiction where such Designated Company has employees, regarding, without limitation, eligibility to participate in the Plan, handling and making of payroll deductions or contribution by other means, establishment of bank or trust accounts to hold payroll deductions, payment of interest, conversion of local currency, obligations to pay payroll tax, withholding procedures and handling of share issuances, any of which may vary according to applicable requirements; provided that if such special rules or sub-plans are inconsistent with the requirements of Section 423(b) of the Code, the employees subject to such special rules or sub-plans will participate in the Non-423 Component.

14.Optionees Not Stockholders. Neither the granting of an Option to a Participant nor the deductions from his or her pay shall result in such Participant becoming a holder of the shares of Common Stock covered by an Option under the Plan until such shares have been purchased by and issued to him or her.

15.Rights Not Transferable. Rights under the Plan are not transferable by a Participant other than by will or the laws of descent and distribution, and are exercisable during the Participant’s lifetime only by the Participant.

16.Application of Funds. All funds received or held by the Company under the Plan may be combined with other corporate funds and may be used for any corporate purpose, unless otherwise required under applicable law.

17.Adjustment in Case of Changes Affecting Common Stock. In the event of a subdivision of outstanding shares of Common Stock, the payment of a dividend in Common Stock or any other change affecting the Common Stock, the number of shares approved for the

Plan and the share limitation set forth in Section 8 shall be equitably or proportionately adjusted to give proper effect to such event.

18.Amendment of the Plan. The Board may at any time and from time to time amend the Plan in any respect, except that without the approval within 12 months of such Board action by the stockholders, no amendment shall be made increasing the number of shares approved for the Plan or making any other change that would require stockholder approval in order for the 423 Component of the Plan, as amended, to qualify as an “employee stock purchase plan” under Section 423(b) of the Code.

19.Insufficient Shares. If the total number of shares of Common Stock that would otherwise be purchased on any Exercise Date plus the number of shares purchased under previous Offerings under the Plan exceeds the maximum number of shares issuable under the Plan, the shares then available shall be apportioned among Participants in proportion to the amount of payroll deductions accumulated on behalf of each Participant that would otherwise be used to purchase Common Stock on such Exercise Date.

20.Termination of the Plan. The Plan may be terminated at any time by the Board. Upon termination of the Plan, all amounts in the accounts of Participants shall be promptly refunded. The Plan shall automatically terminate on the ten year anniversary of the Registration Date.

21.Governmental Regulations. The Company’s obligation to sell and deliver Common Stock under the Plan is subject to the completion of any registration or qualification of the Common Stock under any U.S. or non-U.S. local, state or federal securities or exchange control law, or under rulings or regulations of the U.S. Securities and Exchange Commission (the “SEC”) or of any other governmental regulatory body, and to obtaining any approval or other

clearance from any U.S. and non-U.S. local, state or federal governmental agency, which registration, qualification or approval the Company shall, in its absolute discretion, deem necessary or advisable. The Company is under no obligation to register or qualify the Common Stock with the SEC or any other U.S. or non-U.S. securities commission or to seek approval or clearance from any governmental authority for the issuance or sale of such stock.

22.Governing Law. This Plan and all Options and actions taken thereunder shall be governed by, and construed in accordance with the General Corporation Law of the State of Delaware as to matters within the scope thereof, and as to all other matters shall be governed by and construed in accordance with the internal laws of the State of California applied without regard to conflict of law principles.

23.Issuance of Shares. Shares may be issued upon exercise of an Option from authorized but unissued Common Stock, from shares held in the treasury of the Company, or from any other proper source.

24.Tax Withholding. Participation in the Plan is subject to any applicable U.S. and non-U.S. federal, state or local tax withholding requirements on income the Participant realizes in connection with the Plan. Each Participant agrees, by entering the Plan, that the Company or any Subsidiary or Affiliate may withhold any applicable withholding taxes by any such method as shall be determined by the Company, including by withholding from a Participant’s wages, salary or other compensation or by selling a sufficient number of shares acquired on the Exercise Date to cover applicable withholding taxes. Applicable withholding taxes may include any withholding required to make available to the Company or any Subsidiary or Affiliate any tax deductions or benefits attributable to the sale or disposition of Common Stock by such

Participant. The Company will not be required to issue any Common Stock under the Plan until all withholding obligations are satisfied.

25.Notification Upon Sale of Shares Under 423 Component. Each Participant agrees, by entering the 423 Component of the Plan, to give the Company prompt notice of any disposition of shares purchased under the Plan where such disposition occurs within two years after the date of grant of the Option pursuant to which such shares were purchased or within one year after the date such shares were purchased.

26.Effective Date and Approval of Shareholders. The Plan shall take effect on the date immediately preceding the Registration Date, subject to prior approval by the holders of a majority of the votes cast at a meeting of stockholders at which a quorum is present or by written consent of the stockholders.