2013 Employee Stock Purchase Plan, as amended

The following constitute the provisions of the 2013 Employee Stock Purchase Plan of Infinity Pharmaceuticals, Inc.

1.Purpose. The purpose of the Plan is to provide employees of the Company and its Designated Subsidiaries with an opportunity to purchase Common Stock of the Company through accumulated payroll deductions. It is the intention of the Company to have the Plan qualify as an “Employee Stock Purchase Plan” under Section 423 of the Code. The provisions of the Plan, accordingly, shall be construed so as to extend and limit participation in a manner consistent with the requirements of that section of the Code.

2.Definitions.

3.Eligibility.

(b)Any provisions of the Plan to the contrary notwithstanding, no Citizen- Owner shall be granted an option under the Plan (i) to the extent that, immediately after the grant, such Citizen-Owner (or any other person whose stock would be attributed to such Citizen-Owner pursuant to Section 424(d) of the Code) would own capital stock of the Company or of any Subsidiary and/or hold outstanding options to purchase such stock possessing five percent (5%) or more of the total combined voting power or value of all classes of the capital stock of the Company or of any Subsidiary, or (ii) to the extent that his or her rights to purchase stock under all employee stock purchase plans of the Company and its Subsidiaries accrues at a rate which exceeds Twenty-Five Thousand Dollars ($25,000) worth of stock (determined at the Fair Market Value of the shares at the time such option is granted) for each calendar year in which such option is outstanding at any time. In the event that a Citizen-Owner may not be granted an option under the Plan because of the foregoing restrictions, the Citizen-Owner shall be granted an option to purchase the maximum number of shares that would not violate the foregoing restrictions.

4.Offering Periods. The Plan shall be implemented by consecutive, overlapping Offering Periods with a new Offering Period commencing on the first Trading Day on or after July 1 and January 1 each year, or on such other date as the Board shall determine, and continuing thereafter until terminated in accordance with Section 19 hereof. The Board shall have the power to change the duration of Offering Periods and Purchase Periods (including the commencement dates thereof) with respect to future offerings without stockholder approval.

5.Participation.

(a)An eligible Citizen-Owner may become a participant in the Plan (a “Participant”) by completing a subscription agreement authorizing payroll deductions in the form designated by the Company from time to time and filing it on or prior to the applicable Enrollment Date with the Company’s payroll office or such other office as the Company may direct.

(b)Payroll deductions for a Participant shall commence on the first payroll following the Enrollment Date and shall end on the last payroll in the Offering Period to which such authorization is applicable, unless sooner terminated by the Participant as provided in Section 10 hereof.

6.Payroll Deductions.

(a)At the time a Participant files his or her subscription agreement, he or she shall elect to have payroll deductions made on each pay day during the Offering Period in an amount not exceeding ten percent (10%) of the Compensation which he or she receives on each pay day during the Offering Period. Such payroll deductions shall be in whole percentages only.

(b)All payroll deductions made for a Participant shall be credited to his or her account under the Plan. A Participant may not make any additional payments into such account.

(c)A Participant may discontinue his or her participation in the Plan as provided in Section 10 hereof, or may decrease the rate of his or her payroll deductions during the Offering Period by completing and filing with the Company a new subscription agreement authorizing a change in payroll deduction rate. The Board may, in its discretion, limit the number of participation rate changes during any Offering Period. The change in payroll deduction rate shall be effective with the first full payroll period following ten (10) business days after the Company’s receipt of the new subscription agreement. A Participant’s subscription agreement shall remain in effect for successive Offering Periods unless terminated as provided in Section 10 hereof.

(d)At the time the option (as described in Section 7) is exercised, in whole or in part, or at the time any of the Common Stock issued under the Plan is disposed of, the Participant must make adequate provision for the Company’s federal, state, or other tax withholding obligations, if any, which arise upon the exercise of the option or the disposition of the Common Stock. At any time, the Company may, but shall not be obligated to, withhold from the Participant’s compensation the amount necessary for the Company to meet applicable withholding obligations, including any withholding required to make available to the Company any tax deductions or benefits attributable to sale or other disposition of Common Stock by the Citizen-Owner.

7.Grant of Option. On the Enrollment Date of each Offering Period, each eligible Citizen-Owner participating in such Offering Period shall be granted an option to purchase (at the applicable Purchase Price) up to a whole number of shares of the Common Stock the (“Option Shares”) determined by dividing $50,000 by the Fair Market Value of a share of Common Stock on the Enrollment Date (subject to any adjustment pursuant to Section 18), and provided that such purchase shall be subject to the limitations set forth in Sections 3(b) and 12 hereof. The option shall be exercisable as to 25% of the Option Shares on each Exercise Date during the Offering Period. Exercise of the option shall occur as provided in Section 8 hereof, unless the Citizen-Owner has withdrawn pursuant to Section 10 hereof. The option shall expire on the last day of the Offering Period.

8.Exercise of Option. Unless a Participant withdraws from the Plan as provided in Section 10 hereof, his or her option for the purchase of shares shall be exercised automatically on each Exercise Date during the Offering Period, and a number of full shares not exceeding the number of shares as to which such Participant’s option is exercisable on such Exercise Date shall be purchased for such Participant at the applicable Purchase Price with the accumulated payroll deductions in his or her account. No fractional shares shall be purchased. Any payroll deductions accumulated in a Participant’s account which are not sufficient to purchase a full share of Common Stock shall be retained in the Participant’s account for the subsequent Purchase Period or Offering Period, subject to earlier withdrawal by the Participant as provided in Section 10 hereof. Any other monies left over in a Participant’s account after the Exercise Date shall be returned to the Participant. During a Participant’s lifetime, a Participant’s option to purchase shares hereunder is exercisable only by him or her.

9.Delivery. As promptly as practicable after each Exercise Date on which a purchase of shares occurs, the Company shall arrange the delivery to each Participant or to his or her designee, as appropriate, of a certificate representing the shares purchased upon exercise of his or her option. The Company may, in its sole discretion and in compliance with applicable laws, authorize the use of book entry registration of shares in lieu of issuing certificates.

10.Withdrawal; Termination of Employment.

(a)A Participant may withdraw all but not less than all the payroll deductions credited to his or her account and not yet used to exercise his or her option under the Plan at any time by giving written notice to the Company in the form designated by the Company. All of the Participant’s payroll deductions credited to his or her account shall be paid to such Participant promptly after receipt of notice of withdrawal and such Participant’s option for the Offering Period shall be automatically terminated, and no further payroll deductions for the purchase of shares shall be made for such Offering Period. If a Participant withdraws from an Offering Period, payroll deductions shall not resume at the beginning of the succeeding Offering Period unless the Participant delivers to the Company a new subscription agreement.

(b)Upon a Participant’s ceasing to be a Citizen-Owner, for any reason, he or she shall be deemed to have elected to withdraw from the Plan and the payroll deductions credited to such Participant’s account during the Offering Period but not yet used to exercise the option shall be returned to such Participant or, in the case of his or her death, to the person or persons entitled thereto under Section 14 hereof, and such Participant’s option shall be automatically terminated. If, prior to the last day of the Offering Period, the Designated Subsidiary by which the Citizen-Owner is employed shall cease to be a Subsidiary of the Company, or if the Citizen-Owner is transferred to a Subsidiary of the Company that is not a Designated Subsidiary, the Citizen-Owner shall be deemed to have terminated employment for purposes of this Plan.

(c)A Participant’s withdrawal from an Offering Period shall not have any effect upon his or her eligibility to participate in any similar plan which may hereafter be adopted by the Company or in succeeding Offering Periods.

11.Interest. No interest shall accrue on the payroll deductions of a Participant in the Plan.

12.Stock.

(a)The maximum number of shares of the Common Stock which shall be made available for sale under the Plan shall be 250,000 shares, subject to adjustment as provided in Section 18(a) hereof. If, on a given Exercise Date, the number of shares with respect to which options are to be exercised exceeds the number of shares then available under the Plan, the Company shall make a pro rata allocation of the shares remaining available for purchase in as uniform a manner as shall be practicable and as it shall determine to be equitable.

(b)The Participant shall have no interest or voting right in shares covered by his or her option until such option has been exercised and then only with respect to the Option Shares actually purchased for the account of the Participant.

(c)Shares to be delivered to a Participant under the Plan shall be registered pursuant to instructions (whether written, electronic, or otherwise, but in any case as specified by the Company) provided to the Company by the Participant in the name of the Participant or in the name of the Participant and his or her spouse.

13.Administration. The Plan shall be administered by the Board or a committee of members of the Board appointed by the Board (a “Committee”). The Board or its Committee shall have full and exclusive discretionary authority to construe, interpret and apply the terms of the Plan, to determine eligibility and to adjudicate all disputed claims filed under the Plan. Every finding, decision and determination made by the Board or its Committee shall, to the full extent permitted by law, be final and binding upon all parties. Any reference to the authority of the Committee to act under this Plan shall be contingent upon the Board having delegated such authority to the Committee. All references to the Board contained herein shall also refer to its Committee, as applicable.

14.Designation of Beneficiary.

(a)A Participant may file a written designation of a beneficiary who is to receive any shares and cash, if any, from the Participant’s account under the Plan in the event of such Participant’s death subsequent to an Exercise Date on which the option is exercised but prior to delivery to such Participant of such shares and cash. In addition, a Participant may file a written designation of a beneficiary who is to receive any cash from the Participant’s account under the Plan in the event of such Participant’s death prior to exercise of the option. If a Participant is married and the designated beneficiary is not the spouse, spousal consent shall be required for such designation to be effective.

(b)Such designation of beneficiary may be changed by the Participant at any time by written notice. In the event of the death of a Participant and in the absence of a beneficiary validly designated under the Plan who is living at the time of such Participant’s death, the Company shall deliver such shares and/or cash to the executor or administrator of the estate of the Participant, or if no such executor or administrator has been appointed (to the knowledge of the Company), the Company, in its discretion, may deliver such shares and/or cash to the spouse or to any one or more dependents or relatives of the Participant, or if no spouse, dependent or relative is known to the Company, then to such other person as the Company may designate.

15.Transferability. Neither payroll deductions credited to a Participant’s account nor any rights with regard to the exercise of an option or to receive shares under the Plan may be assigned, transferred, pledged or otherwise disposed of in any way (other than by will, the laws of descent and distribution or as provided in Section 14 hereof) by the Participant. Any such attempt at assignment, transfer, pledge or other disposition shall be without effect, except that the Company may treat such act as an election to withdraw funds from an Offering Period in accordance with Section 10 hereof.

16.Use of Funds. All payroll deductions received or held by the Company under the Plan may be used by the Company for any corporate purpose, and the Company shall not be obligated to segregate such payroll deductions.

17.Reports. Individual accounts shall be maintained for each Participant in the Plan. Statements of account shall be given to Participants at least annually, which statements shall set forth the amounts of payroll deductions, the Purchase Price, the number of shares purchased and the remaining cash balance, if any.

18.Adjustments Upon Changes in Capitalization; Reorganization Events.

(a)Changes in Capitalization. In the event of any stock split, reverse stock split, stock dividend, recapitalization, combination of shares, reclassification of shares, spin-off or other similar change in capitalization or event, or any dividend or distribution to holders of Common Stock other than an ordinary cash dividend, (i) the number and class of securities available under this Plan, (ii) the share limitations set forth in Sections 3 and 7, and (iii) the Purchase Price shall be equitably adjusted to the extent determined by the Board.

(b)Reorganization Events.

(1)Definition. A “Reorganization Event” shall mean: (a) any merger or consolidation of the Company with or into another entity as a result of which all of the Common Stock of the Company is converted into or exchanged for the right to receive cash, securities or other property or is cancelled, (b) any transfer or disposition of all of the Common Stock for cash, securities or other property pursuant to a share exchange or other transaction or (c) any liquidation or dissolution of the Company.

(2)Consequences of a Reorganization Event on Options. In connection with a Reorganization Event, the Board may take any one or more of the following actions as to outstanding options on such terms as the Board determines: (i) provide that options shall be assumed, or substantially equivalent options shall be substituted, by the acquiring or succeeding corporation (or an affiliate thereof), (ii) upon written notice to Citizen-Owners, provide that all outstanding options will be terminated immediately prior to the consummation of such Reorganization Event and that all such outstanding options will become exercisable to the extent of accumulated payroll deductions as of a date specified by the Board in such notice, which date shall not be less than ten (10) days preceding the effective date of the Reorganization Event, (iii) upon written notice to Citizen-Owners, provide that all outstanding options will be cancelled as of a date prior to the effective date of the Reorganization Event and that all accumulated payroll deductions will be returned to participating Citizen-Owners on such date, (iv) in the event of a Reorganization Event under the terms of which holders of Common Stock will receive upon consummation thereof a cash payment for each share surrendered in the Reorganization Event (the “Acquisition Price”), change the last day of the Offering Period to be the date of the consummation of the Reorganization Event and make or provide for a cash payment to each Citizen-Owner equal to (A) (i) the Acquisition Price times (ii) the number of shares of Common Stock that the Citizen-Owner’s accumulated payroll deductions as of immediately prior to the Reorganization Event could purchase at the Purchase Price, where the Acquisition Price is treated as the fair market value of the Common Stock on the last day of the applicable Plan Period for purposes of determining the Purchase Price under Section 2(r) hereof, and where the number of shares that could be purchased is subject to the limitations set forth in Sections 3 and 7, minus (B) the result of multiplying such number of shares by such Purchase Price, (v) provide that, in connection with a liquidation or dissolution of the Company, options shall convert into the right to receive liquidation proceeds (net of the Purchase Price thereof) and (vi) any combination of the foregoing.

For purposes of clause (i) above, an option shall be considered assumed if, following consummation of the Reorganization Event, the replacement option confers the right to purchase, for each share of Common Stock subject to the option immediately prior to the consummation of the Reorganization Event, the consideration (whether cash, securities or other property) received as a result of the Reorganization Event by holders of Common Stock for each share of Common Stock held immediately prior to the consummation of the Reorganization Event (and if holders were offered a choice of consideration, the type of consideration chosen by the holders of a majority of the outstanding shares of Common Stock); provided, however, that if the consideration received as a result of the Reorganization Event is not solely common stock of the acquiring or succeeding corporation (or an affiliate thereof), the Company may, with the consent of the acquiring or succeeding corporation, provide for the consideration to be received upon the exercise of options to consist solely of such number of shares of common stock of the acquiring or succeeding corporation (or an affiliate thereof) that the Board determines to be equivalent in value (as of the date of such determination or another date specified by the Board) to the per share consideration received by holders of outstanding shares of Common Stock as a result of the Reorganization Event.

19.Amendment or Termination.

(a)The Board may at any time and for any reason terminate or amend the Plan. Except as provided in Section 18 hereof, no such termination can affect options previously granted, provided that an Offering Period may be terminated by the Board on any Exercise Date if the Board determines that the termination of the Plan is in the best interests of the Company and its stockholders. Except as provided in Section 18 hereof, no amendment may make any change in any option theretofore granted which adversely affects the rights of any Participant. To the extent necessary to comply with Section 423 of the Code (or any successor rule or provision or any other applicable law or regulation), the Company shall obtain stockholder approval in such a manner and to such a degree as required.

(b)Without stockholder consent and without regard to whether any Participant rights may be considered to have been “adversely affected,” the Board shall be entitled to change the Offering Periods and Purchase Periods, limit the frequency and/or number of changes in the amount withheld during an Offering Period, establish the exchange ratio applicable to amounts withheld in a currency other than U.S. dollars, permit payroll withholding in excess of the amount designated by a Participant in order to adjust for delays or mistakes in the Company’s processing of properly completed withholding elections, establish reasonable waiting and adjustment periods and/or accounting and crediting procedures to ensure that amounts applied toward the purchase of Common Stock for each Participant properly correspond with amounts withheld from the Participant’s Compensation and establish such other limitations or procedures as the Board determines in its sole discretion advisable which are consistent with the Plan.

20.Notices. All notices or other communications by a Participant to the Company under or in connection with the Plan shall be deemed to have been duly given when received in the form specified by the Company at the location, or by the person, designated by the Company for the receipt thereof.

21.Conditions Upon Issuance of Shares. Shares shall not be issued with respect to an option unless the exercise of such option and the issuance and delivery of such shares pursuant thereto shall comply with all applicable provisions of law, domestic or foreign, including, without limitation, the Securities Act of 1933, as amended, the Securities Exchange Act of 1934, as amended, the rules and regulations promulgated thereunder, and the requirements of any stock exchange upon which the shares may then be listed, and shall be further subject to the approval of counsel for the Company with respect to such compliance.

As a condition to the exercise of an option, the Company may require the person exercising such option to represent and warrant at the time of any such exercise that the shares are being purchased only for investment and without any present intention to sell or distribute such shares if, in the opinion of counsel for the Company, such a representation is required by any of the aforementioned applicable provisions of law.

22.Effective Date. The Plan shall become effective upon the earlier to occur of its adoption by the Board or its approval by the stockholders of the Company, which approval must be obtained within 12 months of the date the Plan is adopted by the Board.

23.Automatic Transfer to Low Price Offering Period. To the extent permitted by any applicable laws, regulations, or rules of the established stock exchange, national market system, or over-the-counter market on which the Common Stock trades, if the Fair Market Value of the Common Stock on the Enrollment Date of the next Offering Period is lower than the Fair Market Value of the Common Stock on the Enrollment Date of any current Offering Period, then all Participants in such current Offering Period shall be automatically withdrawn from such Offering Period immediately after the exercise of their option on the Exercise Date and shall be automatically re-enrolled in the next Offering Period as of the first day thereof.

24.Governmental Regulations. The Company’s obligation to sell and deliver Common Stock under this Plan is subject to listing on an established stock exchange or quotation on a national market system or an over the counter market (to the extent the Common Stock is then so listed or quoted) and the approval of all governmental authorities required in connection with the authorization, issuance, or sale of such stock.

25.Governing Law. The Plan shall be governed by Delaware law except to the extent that such law is preempted by federal law.

26.Source 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.

27.Notification Upon Sale of Shares. Each Citizen-Owner agrees, by participating in the Plan, to promptly give notice to the Company of any disposition of shares purchased under the Plan where such disposition occurs within two years after the Enrollment Date with respect to the option pursuant to which such shares were purchased or within one year of the date of exercise of such option pursuant to which such shares were purchased.

28.Grants to Employees in Foreign Jurisdictions. The Company may, to comply with the laws of a foreign jurisdiction, grant options to Citizen-Owners of the Company or a Designated Subsidiary who are citizens or residents of such foreign jurisdiction (without regard to whether they are also citizens of the United States or resident aliens (within the meaning of Section 7701(b)(1)(A) of the Code)) with terms that are less favorable (but not more favorable) than the terms of options granted under the Plan to Citizen-Owners of the Company or a Designated Subsidiary who are resident in the United States. Notwithstanding the preceding provisions of this Plan, Citizen-Owners of the Company or a Designated Subsidiary who are citizens or residents of a foreign jurisdiction (without regard to whether they are also citizens of the United States or resident aliens (within the meaning of Section 7701(b)(1)(A) of the Code)) may be excluded from eligibility under the Plan if (a) the grant of an option under the Plan to a citizen or resident of the foreign jurisdiction is prohibited under the laws of such jurisdiction or (b) compliance with the laws of the foreign jurisdiction would cause the Plan to violate the requirements of Section 423 of the Code. The Company may add one or more appendices to this Plan describing the operation of the Plan in those foreign jurisdictions in which Citizen-Owners are excluded from participation or granted less favorable options.

29.Authorization of Sub-Plans. The Board may from time to time establish one or more sub-plans under the Plan with respect to one or more Designated Subsidiaries, provided that such sub-plan complies with Section 423 of the Code.

Adopted by the Board of Directors

on March 6, 2013

Approved by the stockholders

on June 11, 2013

The 2013 Employee Stock Purchase Plan (the “Plan”) of Infinity Pharmaceuticals, Inc. is hereby amended as follows:

1.Section 6(c) of the Plan is hereby deleted and new Section 6(c) is inserted in lieu thereof which shall read as follows:

“(c) A Participant may discontinue his or her participation in the Plan as provided in Section 10 hereof, or may increase or decrease the rate of his or her payroll deductions during the Offering Period by completing and filing with the Company a new subscription agreement authorizing a change in payroll deduction rate. The Board may, in its discretion, limit the number of participation rate changes during any Offering Period. The change in payroll deduction rate shall be effective with the first full payroll period following ten (10) business days after the Company’s receipt of the new subscription agreement. A Participant’s subscription agreement shall remain in effect for successive Offering Periods unless terminated as provided in Section 10 hereof.”

Except as set forth above, the remainder of the Plan remains in full force and effect.

The 2013 Employee Stock Purchase Plan (the “Plan”) of Infinity Pharmaceuticals, Inc. is hereby amended as follows:

1.Section 12(a) of the Plan is hereby deleted and a new Section 12(a) is inserted in lieu thereof which shall read as follows:

“(a)    The maximum number of shares of the Common Stock which shall be made available for sale under the Plan shall be 400,000 shares, subject to adjustment as provided in Section 18(a) hereof. If, on a given Exercise Date, the number of shares with respect to which options are to be exercised exceeds the number of shares then available under the Plan, the Company shall make a pro rata allocation of the shares remaining available for purchase in as uniform a manner as shall be practicable and as it shall determine to be equitable.”

Except as set forth above, the remainder of the Plan remains in full force and effect.

The 2013 Employee Stock Purchase Plan (the “Plan”) of Infinity Pharmaceuticals, Inc. is hereby amended as follows:

1.Section 12(a) of the Plan is hereby deleted and a new Section 12(a) is inserted in lieu thereof which shall read as follows:

“(a)    The maximum number of shares of the Common Stock which shall be made available for sale under the Plan shall be 600,000 shares, subject to adjustment as provided in Section 18(a) hereof. If, on a given Exercise Date, the number of shares with respect to which options are to be exercised exceeds the number of shares then available under the Plan, the Company shall make a pro rata allocation of the shares remaining available for purchase in as uniform a manner as shall be practicable and as it shall determine to be equitable.”

Except as set forth above, the remainder of the Plan remains in full force and effect.