EX-10.3(a)





 Exhibit 10.3(a) 

BIOMEA FUSION, INC. 

2020 EQUITY INCENTIVE PLAN 

As Adopted December 18, 2020 

1. Purpose. 
 The purpose
of the Plan is to advance the interests of the Company’s stockholders by enhancing the Company’s ability to attract, retain and motivate persons who make (or are expected to make) important contributions to the Company by providing such
persons with equity ownership opportunities and thereby better aligning the interests of such persons with those of the Company’s stockholders. Capitalized terms used in the Plan are defined in Section 11 below. 

2. Eligibility.  

Service Providers are eligible to be granted Awards under the Plan, subject to the limitations described herein. 

3. Administration and Delegation. 

3.1 Administration. The Plan will be administered by the Administrator. The Administrator shall have authority to determine which
Service Providers will receive Awards, to grant Awards and to set all terms and conditions of Awards (including, but not limited to, vesting, exercise and forfeiture provisions). In addition, the Administrator shall have the authority to take all
actions and make all determinations contemplated by the Plan and to adopt, amend and repeal such administrative rules, guidelines and practices relating to the Plan as it shall deem advisable. The Administrator may correct any defect or ambiguity,
supply any omission or reconcile any inconsistency in the Plan or any Award in the manner and to the extent it shall deem necessary or appropriate to carry the Plan and any Awards into effect, as determined by the Administrator. The Administrator
shall make all determinations under the Plan in the Administrator’s sole discretion and all such determinations shall be final and binding on all persons having or claiming any interest in the Plan or in any Award. 

3.2 Appointment of Committees. To the extent permitted by Applicable Laws, the Board may delegate any or all of its powers under
the Plan to one or more Committees. The Board may abolish any Committee at any time and re-vest in itself any previously delegated authority. 

4. Stock Available for Awards. 

4.1 Number of Shares. Subject to adjustment under Section 8 hereof, Awards may be made under the Plan covering up to 489,570
shares of Common Stock; provided, however, that the Plan Limit shall automatically be increased by the number of shares of Conversion Common Stock (as defined below), that terminate, expire or lapse or are repurchased for any reason
following the date of adoption of this Plan, in an amount not to exceed 93,262. If any Award expires or lapses or is terminated, surrendered or canceled without having been fully exercised or is forfeited in whole or in part (including as the result
of shares of Common Stock subject to such 












 
Award being repurchased by the Company at or below the original issuance price), in any case in a manner that results in any shares of Common Stock covered by such Award not being issued or being
so reacquired by the Company, the unused Common Stock covered by such Award shall again be available for the grant of Awards under the Plan. Further, shares of Common Stock delivered (either by actual delivery or attestation) to the Company by a
Participant to satisfy the applicable exercise or purchase price of an Award and/or to satisfy any applicable tax withholding obligation (including shares retained by the Company from the Award being exercised or purchased and/or creating the tax
obligation) shall be added to the number of shares of Common Stock available for the grant of Awards under the Plan. However, in the case of Incentive Stock Options (as hereinafter defined), the foregoing provisions shall be subject to any
limitations under the Code. Shares of Common Stock issued under the Plan may consist in whole or in part of authorized but unissued shares, shares purchased on the open market or treasury shares. For purposes hereof, 

4.2 Substitute Awards. In connection with a merger or consolidation of an entity with the Company or the acquisition by the Company of
property or stock of an entity, the Administrator may grant Awards in substitution for any options or other stock or stock-based awards granted prior to such merger or consolidation by such entity or an affiliate thereof. Substitute Awards may be
granted on such terms as the Administrator deems appropriate in the circumstances, notwithstanding any limitations on Awards contained in the Plan. Substitute Awards shall not count against the overall share limit set forth in Section 4.1
hereof, except as may be required by reason of Section 422 of the Code. 
 5. Stock Options. 

5.1 General. The Administrator may grant Options to any Service Provider, subject to the limitations on Incentive Stock Options
described below. The Administrator shall determine the number of shares of Common Stock to be covered by each Option, the exercise price of each Option and the conditions and limitations applicable to the exercise of each Option, including
conditions relating to Applicable Laws, as it considers necessary or advisable. 
 5.2 Incentive Stock Options. The
Administrator may grant Options intended to qualify as Incentive Stock Options only to employees of the Company, any of the Company’s present or future “parent corporations” or “subsidiary corporations” as defined in
Sections 424(e) or (f) of the Code, respectively, and any other entities the employees of which are eligible to receive Incentive Stock Options under the Code. All Options intended to qualify as Incentive Stock Options shall be subject to and
shall be construed consistently with the requirements of Section 422 of the Code. Neither the Company nor the Administrator shall have any liability to a Participant, or any other party, (i) if an Option (or any part thereof) which is
intended to qualify as an Incentive Stock Option fails to qualify as an Incentive Stock Option or (ii) for any action or omission by the Administrator that causes an Option not to qualify as an Incentive Stock Option, including without
limitation, the conversion of an Incentive Stock Option to a Non-Qualified Stock Option or the grant of an Option intended as an Incentive Stock Option that fails to satisfy the requirements under the Code
applicable to an Incentive Stock Option. Any Option that is intended to qualify as an Incentive Stock Option, but fails to so qualify for any reason, including without limitation, the portion of any Option becoming exercisable in excess of the
$100,000 limitation described in Treasury Regulation Section 1.422-4, shall be treated as a Non-Qualified Stock Option for all purposes. 

  
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 5.3 Exercise Price. The Administrator shall establish the exercise price of
each Option and specify the exercise price in the applicable Award Agreement. The exercise price shall be not less than 100% of the Fair Market Value on the date the Option is granted. In the case of an Incentive Stock Option granted to an employee
who, at the time of grant of the Option, owns (or is treated as owning under Section 424 of the Code) stock representing more than 10% of the voting power of all classes of stock of the Company (or a “parent corporation” or
“subsidiary corporation” thereof within the meaning of Sections 424(e) or 424(f) of the Code, respectively), the per share exercise price shall be no less than 110% of the Fair Market Value on the date the Option is granted. 

5.4 Duration of Options. Each Option shall be exercisable at such times and subject to such terms and conditions as the
Administrator may specify in the applicable Award Agreement, provided that the term of any Option shall not exceed ten years. In the case of an Incentive Stock Option granted to an employee who, at the time of grant of the Option, owns
(or is treated as owning under Section 424 of the Code) stock representing more than 10% of the voting power of all classes of stock of the Company (or a “parent corporation” or “subsidiary corporation” thereof within the
meaning of Sections 424(e) or 424(f) of the Code, respectively), the term of the Option shall not exceed five years. 
 5.5 Exercise of
Option; Notification of Disposition. Options may be exercised by delivery to the Company of a written notice of exercise, in a form approved by the Administrator (which may be an electronic form), signed by the person authorized to
exercise the Option, together with payment in full (i) as specified in Section 5.6 hereof for the number of shares for which the Option is exercised and (ii) as specified in Section 9.5 hereof for any applicable withholding
taxes. Unless otherwise determined by the Administrator, an Option may not be exercised for a fraction of a share of Common Stock. If an Option is designated as an Incentive Stock Option, the Participant shall give prompt notice to the Company of
any disposition or other transfer of any shares of Common Stock acquired from the Option if such disposition or transfer is made (i) within two years from the grant date with respect to such Option or (ii) within one year after the
transfer of such shares to the Participant (other than any such disposition made in connection with a Change in Control). Such notice shall specify the date of such disposition or other transfer and the amount realized, in cash, other property,
assumption of indebtedness or other consideration, by the Participant in such disposition or other transfer. 
 5.6 Payment Upon
Exercise. Common Stock purchased upon the exercise of an Option granted under the Plan shall be paid for in cash or by check, payable to the order of the Company, or, to the extent permitted by the Administrator, by: 

(a) (A) delivery of an irrevocable and unconditional undertaking by a broker acceptable to the Company to deliver promptly to the Company
sufficient funds to pay the exercise price and any required tax withholding, or (B) delivery by the Participant to the Company of a copy of irrevocable and unconditional instructions to a broker acceptable to the Company to deliver promptly to
the Company cash or a check sufficient to pay the exercise price and any required tax withholding; 

  
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 (b) delivery (either by actual delivery or attestation) of shares of Common Stock owned by
the Participant valued at their Fair Market Value, provided (A) such method of payment is then permitted under Applicable Laws, (B) such Common Stock, if acquired directly from the Company, was owned by the Participant for such minimum
period of time, if any, as may be established by the Company at any time, and (C) such Common Stock is not subject to any repurchase, forfeiture, unfulfilled vesting or other similar requirements; 

(c) surrendering shares of Common Stock then issuable upon exercise of the Option valued at their Fair Market Value on the date of exercise;

 (d) delivery of a promissory note of the Participant to the Company on terms determined by the Administrator; 

(e) delivery of property of any other kind which constitutes good and valuable consideration as determined by the Administrator; or 

(f) any combination of the above permitted forms of payment (including cash or check). 

5.7 Early Exercise of Options. The Administrator may provide in the terms of an Award Agreement that the Service Provider may exercise
an Option in whole or in part prior to the full vesting of the Option in exchange for unvested shares of Restricted Stock with respect to any unvested portion of the Option so exercised. Shares of Restricted Stock acquired upon the exercise of any
unvested portion of an Option shall be subject to such terms and conditions as the Administrator shall determine. 
 6. Restricted Stock;
Restricted Stock Units. 
 6.1 General. The Administrator may grant Restricted Stock, or the right to purchase Restricted
Stock, to any Service Provider, subject to the right of the Company to repurchase all or part of such shares at their issue price or other stated or formula price from the Participant (or to require forfeiture of such shares if issued at no cost) in
the event that conditions specified by the Administrator in the applicable Award Agreement are not satisfied prior to the end of the applicable restriction period or periods established by the Administrator for such Award. In addition, the
Administrator may grant to Service Providers Restricted Stock Units, which may be subject to vesting and forfeiture conditions during applicable restriction period or periods, as set forth in an applicable Award Agreement. 

6.2 Terms and Conditions for All Restricted Stock and Restricted Stock Unit Awards. The Administrator shall determine and set forth in
the applicable Award Agreement the terms and conditions applicable to each Restricted Stock and Restricted Stock Unit Award, including the conditions for vesting and repurchase (or forfeiture) and the issue price, in each case, if any. 

  
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 6.3 Additional Provisions Relating to Restricted Stock. 

(a) Dividends. Participants holding shares of Restricted Stock will be entitled to all ordinary cash dividends paid with respect to
such shares to the extent such dividends have a record date that is on or after the date on which the Participant to whom such Restricted Shares are granted becomes the record holder of such Restricted Shares, unless otherwise provided by the
Administrator in the applicable Award Agreement. In addition, unless otherwise provided by the Administrator, if any dividends or distributions are paid in shares, or consist of a dividend or distribution to holders of Common Stock of property other
than an ordinary cash dividend, the shares or other property will be subject to the same restrictions on transferability and forfeitability as the shares of Restricted Stock with respect to which they were paid. Each dividend payment will be made as
provided in the applicable Award Agreement, but in no event later than the end of the calendar year in which the dividends are paid to stockholders of that class of stock or, if later, the 15th day of the third month following the later of
(A) the date the dividends are paid to stockholders of that class of stock, and (B) the date the dividends are no longer subject to forfeiture. 

(b) Stock Certificates. The Company may require that any stock certificates issued in respect of shares of Restricted Stock be
deposited in escrow by the Participant, together with a stock power endorsed in blank, with the Company (or its designee). 
 6.4
Additional Provisions Relating to Restricted Stock Units. 
 (a) Settlement. Upon the vesting of a Restricted Stock Unit, the
Participant shall be entitled to receive from the Company one share of Common Stock or an amount of cash or other property equal to the Fair Market Value of one share of Common Stock on the settlement date, as the Administrator shall determine and
as provided in the applicable Award Agreement. The Administrator may provide that settlement of Restricted Stock Units shall occur upon or as soon as reasonably practicable after the vesting of the Restricted Stock Units or shall instead be
deferred, on a mandatory basis or at the election of the Participant, in a manner that complies with Section 409A.
 (b) Voting
Rights. A Participant shall have no voting rights with respect to any Restricted Stock Units unless and until shares are delivered in settlement thereof.

(c) Dividend Equivalents. To the extent provided by the Administrator, a grant of Restricted Stock Units may provide a Participant with
the right to receive Dividend Equivalents. Dividend Equivalents may be paid currently or credited to an account for the Participant, may be settled in cash and/or shares of Common Stock and may be subject to the same restrictions on transfer and
forfeitability as the Restricted Stock Units with respect to which the Dividend Equivalents are paid, as determined by the Administrator, subject, in each case, to such terms and conditions as the Administrator shall establish and set forth in the
applicable Award Agreement. 
 7. Other Stock-Based Awards.  

Other Stock-Based Awards may be granted hereunder to Participants, including, without limitation, Awards entitling Participants to receive
shares of Common Stock to be delivered in the future. Such Other Stock-Based Awards shall also be available as a form of payment in the settlement of other Awards granted under the Plan, as stand-alone payments and/or as payment in lieu of
compensation to which a Participant is otherwise entitled. Other Stock-Based Awards may be paid in shares of Common Stock, cash or other property, as the Administrator shall determine. Subject to the provisions of the Plan, the Administrator shall
determine the terms and conditions of each Other Stock-Based Award, including any purchase price, transfer restrictions, vesting conditions and other terms and conditions applicable thereto, which shall be set forth in the applicable Award
Agreement. 

  
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 8. Adjustments for Changes in Common Stock and Certain Other Events. 

8.1 In the event that the Administrator determines that any dividend or other distribution (whether in the form of cash, Common Stock, other
securities, or other property), reorganization, merger, consolidation, combination, repurchase, recapitalization, liquidation, dissolution, or sale, transfer, exchange or other disposition of all or substantially all of the assets of the Company, or
sale or exchange of Common Stock or other securities of the Company, issuance of warrants or other rights to purchase Common Stock or other securities of the Company, or other similar corporate transaction or event, as determined by the
Administrator, affects the Common Stock such that an adjustment is determined by the Administrator to be appropriate in order to prevent dilution or enlargement of the benefits or potential benefits intended by the Company to be made available under
the Plan or with respect to any Award, then the Administrator may, in such manner as it may deem equitable, adjust any or all of: 
 (a) the
number and kind of shares of Common Stock (or other securities or property) with respect to which Awards may be granted or awarded (including, but not limited to, adjustments of the limitations in Section 4 hereof on the maximum number and kind
of shares which may be issued); 
 (b) the number and kind of shares of Common Stock (or other securities or property) subject to
outstanding Awards; 
 (c) the grant or exercise price with respect to any Award; and 

(d) the terms and conditions of any Awards (including, without limitation, any applicable financial or other performance “targets”
specified in an Award Agreement). 
 8.2 In the event of any transaction or event described in Section 8.1 hereof (including without
limitation any Change in Control) or any unusual or nonrecurring transaction or event affecting the Company or the financial statements of the Company, or any change in any Applicable Laws or accounting principles, the Administrator, on such terms
and conditions as it deems appropriate, either by the terms of the Award or by action taken prior to the occurrence of such transaction or event and either automatically or upon the Participant’s request, is hereby authorized to take any one or
more of the following actions whenever the Administrator determines that such action is appropriate in order to (x) prevent dilution or enlargement of the benefits or potential benefits intended by the Company to be made available under the
Plan or with respect to any Award granted or issued under the Plan, (y) to facilitate such transaction or event or (z) give effect to such changes in Applicable Laws or accounting principles:  

  
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 (a) To provide for the cancellation of any such Award in exchange for either an amount of
cash or other property with a value equal to the amount that could have been obtained upon the exercise or settlement of the vested portion of such Award or realization of the Participant’s rights under the vested portion of such Award, as
applicable; provided that, if the amount that could have been obtained upon the exercise or settlement of the vested portion of such Award or realization of the Participant’s rights, in any case, is equal to or less than zero,
then the vested portion of such Award may be terminated without payment; 
 (b) To provide that such Award shall vest and, to the extent
applicable, be exercisable as to all shares covered thereby, notwithstanding anything to the contrary in the Plan or the provisions of such Award; 

(c) To provide that such Award be assumed by the successor or survivor corporation, or a parent or subsidiary thereof, or shall be substituted
for by awards covering the stock of the successor or survivor corporation, or a parent or subsidiary thereof, with appropriate adjustments as to the number and kind of shares and applicable exercise or purchase price, in all cases, as determined by
the Administrator; 
 (d) To make adjustments in the number and type of shares of Common Stock (or other securities or property) subject to
outstanding Awards, and/or in the terms and conditions of (including the grant or exercise price), and the criteria included in, outstanding Awards which may be granted in the future; 

(e) To replace such Award with other rights or property selected by the Administrator; and/or 

(f) To provide that the Award will terminate and cannot vest, be exercised or become payable after the applicable event. 

8.3 In connection with the occurrence of any Equity Restructuring, and notwithstanding anything to the contrary in this Section 8, the
Administrator will equitably adjust each outstanding Award, which adjustments may include adjustments to the number and type of securities subject to each outstanding Award and/or the exercise price or grant price thereof, if applicable, the grant
of new Awards to Participants, and/or the making of a cash payment to Participants, as the Administrator deems appropriate to reflect such Equity Restructuring. The adjustments provided under this Section 8.3 shall be nondiscretionary and shall
be final and binding on the affected Participant and the Company; provided that whether an adjustment is equitable shall be determined by the Administrator. 

8.4 In the event of any pending stock dividend, stock split, combination or exchange of shares, merger, consolidation or other distribution
(other than normal cash dividends) of Company assets to stockholders, or any other change affecting the shares of Common Stock or the share price of the Common Stock, including any Equity Restructuring, for reasons of administrative convenience the
Administrator may refuse to permit the exercise of any Award during a period of up to 30 days prior to the consummation of any such transaction. 

8.5 Except as expressly provided in the Plan or pursuant to action of the Administrator under the Plan, no Participant shall have any rights by
reason of any subdivision or consolidation of shares of stock of any class, the payment of any dividend, any increase or decrease in the number of shares of stock of any class or any dissolution, liquidation, merger, or consolidation of the Company
or any other corporation. Except as expressly provided in the Plan 

  
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or pursuant to action of the Administrator under the Plan, no issuance by the Company of shares of stock of any class, or securities convertible into shares of stock of any class, shall affect,
and no adjustment by reason thereof shall be made with respect to, the number of shares of Common Stock subject to an Award or the grant or exercise price of any Award. The existence of the Plan, any Award Agreements and the Awards granted hereunder
shall not affect or restrict in any way the right or power of the Company to make or authorize (i) any adjustment, recapitalization, reorganization or other change in the Company’s capital structure or its business, (ii) any merger,
consolidation dissolution or liquidation of the Company or sale of Company assets or (iii) any sale or issuance of securities, including without limitation, securities with rights superior to those of the Common Stock or which are convertible
into or exchangeable for Common Stock. The Administrator may treat Participants and Awards (or portions thereof) differently under this Section 8. 

9. General Provisions Applicable to Awards.  

9.1 Transferability. Except as the Administrator may otherwise determine or provide in an Award Agreement or otherwise, in any
case in accordance with Applicable Laws, Awards shall not be sold, assigned, transferred, pledged or otherwise encumbered by the person to whom they are granted, either voluntarily or by operation of law, except by will or the laws of descent and
distribution, and, during the life of the Participant, shall be exercisable only by the Participant. References to a Participant, to the extent relevant in the context, shall include references to authorized transferees. 

9.2 Documentation. Each Award shall be evidenced in an Award Agreement, which may be in such form (written, electronic or
otherwise) as the Administrator shall determine. Each Award may contain terms and conditions in addition to those set forth in the Plan. 

9.3 Discretion. Except as otherwise provided by the Plan, each Award may be made alone or in addition or in relation to any other
Award. The terms of each Award to a Participant need not be identical, and the Administrator need not treat Participants or Awards (or portions thereof) uniformly. 

9.4 Termination of Status. The Administrator shall determine the effect on an Award of the disability, death, retirement,
authorized leave of absence or any other change or purported change in a Participant’s Service Provider status and the extent to which, and the period during which, the Participant, the Participant’s legal representative, conservator,
guardian or Designated Beneficiary may exercise rights under the Award, if applicable. 
 9.5 Withholding. Each Participant
shall pay to the Company, or make provision satisfactory to the Administrator for payment of, any taxes required by law to be withheld in connection with Awards to such Participant no later than the date of the event creating the tax liability.
Except as the Administrator may otherwise determine, all such payments shall be made in cash or by certified check. Notwithstanding the foregoing, to the extent permitted by the Administrator, Participants may satisfy such tax obligations in whole
or in part by delivery of shares of Common Stock, including shares retained from the Award creating the tax obligation, valued at their Fair Market Value. The Company may, to the extent permitted by Applicable Laws, deduct any such tax obligations
from any payment of any kind otherwise due to a Participant. 

  
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 9.6 Amendment of Award. The Administrator may amend, modify or terminate any
outstanding Award, including but not limited to, substituting therefor another Award of the same or a different type, changing the date of exercise or settlement, and converting an Incentive Stock Option to a
Non-Qualified Stock Option. The Participant’s consent to such action shall be required unless (i) the Administrator determines that the action, taking into account any related action, would not
materially and adversely affect the Participant, or (ii) the change is permitted under Section 8 and 10.6 hereof. 
 9.7
Conditions on Delivery of Stock. The Company will not be obligated to deliver any shares of Common Stock pursuant to the Plan or to remove restrictions from shares previously delivered under the Plan until (i) all conditions of
the Award have been met or removed to the satisfaction of the Company, (ii) in the opinion of the Company’s counsel, all other legal matters in connection with the issuance and delivery of such shares have been satisfied, including any
applicable securities laws and any applicable stock exchange or stock market rules and regulations, and (iii) the Participant has executed and delivered to the Company such representations or agreements as the Administrator deems necessary or
appropriate to satisfy the requirements of any Applicable Laws. The inability of the Company to obtain authority from any regulatory body having jurisdiction, which authority is determined by the Administrator to be necessary to the lawful issuance
and sale of any securities hereunder, shall relieve the Company of any liability in respect of the failure to issue or sell such shares as to which such requisite authority shall not have been obtained. 

9.8 Acceleration. The Administrator may at any time provide that any Award shall become immediately vested and/or exercisable in
full or in part, free of some or all restrictions or conditions, or otherwise realizable in full or in part, as the case may be. 
 10.
Miscellaneous.  
 10.1 No Right To Employment or Other Status. No person shall have any claim or right to be
granted an Award, and the grant of an Award shall not be construed as giving a Participant the right to continued employment or any other relationship with the Company. The Company expressly reserves the right at any time to dismiss or otherwise
terminate its relationship with a Participant free from any liability or claim under the Plan or any Award, except as expressly provided in an applicable Award Agreement. 

10.2 No Rights As Stockholder; Certificates. Subject to the provisions of the applicable Award Agreement, no Participant or
Designated Beneficiary shall have any rights as a stockholder with respect to any shares of Common Stock to be distributed with respect to an Award until becoming the record holder of such shares. Notwithstanding any other provision of the Plan,
unless otherwise determined by the Administrator or required by any Applicable Laws, the Company shall not be required to deliver to any Participant certificates evidencing shares of Common Stock issued in connection with any Award and instead such
shares of Common Stock may be recorded in the books of the Company (or, as applicable, its transfer agent or stock plan administrator). The Company may place legends on any stock certificates issued under the Plan deemed necessary or appropriate by
the Administrator in order to comply with Applicable Laws. 

  
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 10.3 Effective Date and Term of Plan. The Plan shall become effective on the
date on which it is adopted by the Board. No Awards shall be granted under the Plan after the completion of ten years from the earlier of (i) the date on which the Plan was adopted by the Board or (ii) the date the Plan was approved by the
Company’s stockholders, but Awards previously granted may extend beyond that date in accordance with the terms of the Plan. 
 10.4
Amendment of Plan. The Administrator may amend, suspend or terminate the Plan or any portion thereof at any time; provided that no amendment of the Plan shall materially and adversely affect any Award outstanding at the
time of such amendment without the consent of the affected Participant. Awards outstanding under the Plan at the time of any suspension or termination of the Plan shall continue to be governed in accordance with the terms of the Plan and the
applicable Award Agreement, as in effect prior to such suspension or termination. The Board shall obtain stockholder approval of any Plan amendment to the extent necessary to comply with Applicable Laws. 

10.5 Provisions for Foreign Participants. The Administrator may modify Awards granted to Participants who are foreign nationals or
employed outside the United States or establish subplans or procedures under the Plan to address differences in laws, rules, regulations or customs of such foreign jurisdictions with respect to tax, securities, currency, employee benefit or other
matters. 
 10.6 Section 409A. 

(a) General. The Company intends that all Awards be structured in compliance with, or to satisfy an exemption from, Section 409A,
such that no adverse tax consequences, interest, or penalties under Section 409A apply in connection with any Awards. Notwithstanding anything herein or in any Award Agreement to the contrary, the Administrator may, without a Participant’s
prior consent, amend this Plan and/or Awards, adopt policies and procedures, or take any other actions (including amendments, policies, procedures and actions with retroactive effect) as are necessary or appropriate to preserve the intended tax
treatment of Awards under the Plan, including without limitation, any such actions intended to (A) exempt this Plan and/or any Award from the application of Section 409A, and/or (B) comply with the requirements of Section 409A,
including without limitation any such regulations, guidance, compliance programs and other interpretative authority that may be issued after the date of grant of any Award. The Company makes no representations or warranties as to the tax treatment
of any Award under Section 409A or otherwise. The Company shall have no obligation under this Section 10.6 or otherwise to take any action (whether or not described herein) to avoid the imposition of taxes, penalties or interest under
Section 409A with respect to any Award and shall have no liability to any Participant or any other person if any Award, compensation or other benefits under the Plan are determined to constitute
non-compliant, “nonqualified deferred compensation” subject to the imposition of taxes, penalties and/or interest under Section 409A. 

(b) Separation from Service. With respect to any Award that constitutes “nonqualified deferred compensation” under
Section 409A, any payment or settlement of such Award that is to be made upon a termination of a Participant’s Service Provider relationship shall, to the extent necessary to avoid the imposition of taxes under Section 409A, be made
only upon the Participant’s “separation from service” (within the meaning of Section 409A), whether such “separation from service” occurs upon or subsequent to the termination of the Participant’s Service Provider
relationship. For purposes of any such provision of this Plan or any Award Agreement relating to any such payments or benefits, references to a “termination,” “termination of employment” or like terms shall mean “separation
from service.” 

  
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 (c) Payments to Specified Employees. Notwithstanding any contrary provision in
the Plan or any Award Agreement, any payment(s) of “nonqualified deferred compensation” that are otherwise required to be made under an Award to a “specified employee” (as defined under Section 409A and determined by
the Administrator) as a result of his or her “separation from service” shall, to the extent necessary to avoid the imposition of taxes under Code Section 409A(a)(2)(B)(i), be delayed until the expiration of the six-month period immediately following such “separation from service” (or, if earlier, until the date of death of the specified employee) and shall instead be paid (in a manner set forth in the Award
agreement) on the day that immediately follows the end of such six-month period or as soon as administratively practicable thereafter (without interest). Any payments of “nonqualified deferred
compensation” under such Award that are, by their terms, payable more than six months following the Participant’s “separation from service” shall be paid at the time or times such payments are otherwise scheduled to be made. 

10.7 Limitations on Liability. Notwithstanding any other provisions of the Plan, no individual acting as a director, officer, other
employee or agent of the Company will be liable to any Participant, former Participant, spouse, beneficiary, or any other person for any claim, loss, liability, or expense incurred in connection with the Plan or any Award, nor will such individual
be personally liable with respect to the Plan because of any contract or other instrument he or she executes in his or her capacity as an Administrator, director, officer, other employee or agent of the Company. The Company will indemnify and hold
harmless each director, officer, other employee and agent of the Company to whom any duty or power relating to the administration or interpretation of the Plan has been or will be granted or delegated, against any cost or expense (including
attorneys’ fees) or liability (including any sum paid in settlement of a claim with the Administrator’s approval) arising out of any act or omission to act concerning this Plan unless arising out of such person’s own fraud or bad
faith.
 10.8 Lock-Up Period. Participants shall not offer, pledge, sell, contract to sell,
sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any Common Stock (or other securities) of the
Company or enter into any swap, hedging or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of any Common Stock (or other securities) of the Company held by Participant (other than those
included in the registration) for a period specified by the representative of the underwriters of Common Stock (or other securities) of the Company not to exceed 180 days following the effective date of any registration statement of the Company
filed under the Securities Act (or such other period as may be requested by the Company or the underwriters to accommodate regulatory restrictions on (i) the publication or other distribution of research reports and (ii) analyst
recommendations and opinions, including, but not limited to, the restrictions contained in FINRA Rule 2241, or any successor provisions or amendments thereto). Participants shall execute and deliver such other agreements as may be reasonably
requested by the Company or the underwriter which are consistent with the foregoing or which are necessary to give further effect thereto. The 

  
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obligations described in this Section 10.8 shall not apply to a registration relating solely to employee benefit plans on Form S-1 or Form S-8 or similar forms that may be promulgated in the future, or a registration relating solely to a Securities and Exchange Commission Rule 145 transaction on Form S-4 or
similar forms that may be promulgated in the future. The Company may impose stop-transfer instructions with respect to the shares of Common Stock (or other securities) subject to the foregoing restriction until the end of said 180 day (or other)
period. 
 10.9 Limitations on Transfer. A Participant shall not sell, assign, transfer, pledge, hypothecate or otherwise dispose of,
by operation of law or otherwise (collectively “Transfer”) any interest in any shares of Common Stock held by Participant except in compliance with the provisions herein, in the Company’s Bylaws and applicable securities laws.
Furthermore, the shares of Common Stock shall be subject to a right of first refusal in favor of the Company or its assignees as set forth in the Company’s Bylaws. Notwithstanding the foregoing, Participant may, subject to compliance with the
transfer restrictions set forth in the Company’s Bylaws, transfer shares of Common Stock to or for the benefit of any spouse, children, parents, uncles, aunts, siblings, grandchildren and any other relatives approved by the Board of Directors
(collectively, “Approved Relatives”) or to a trust established solely for the benefit of the Participant and/or Approved Relatives, provided that such shares of Common Stock shall remain subject to the provisions of this Plan
and any other applicable agreements, 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 Plan and
any other applicable agreements. The Company shall not be required (a) to transfer on its books any of the shares of Common Stock that have been sold or otherwise transferred in violation of any of the provisions of this Plan, any other
applicable agreement or the provisions of the Company’s Bylaws or (b) to treat as owner of such shares of Common Stock or to accord the right to vote or pay dividends to any purchaser or other transferee to whom any such shares of Common
Stock shall have been so sold or transferred. 
 10.10 Data Privacy. As a condition of receipt of any Award, each Participant
explicitly and unambiguously consents to the collection, use and transfer, in electronic or other form, of personal data as described in this paragraph by and among, as applicable, the Company and its subsidiaries and affiliates for the exclusive
purpose of implementing, administering and managing the Participant’s participation in the Plan. The Company and its subsidiaries and affiliates may hold certain personal information about a Participant, including but not limited to, the
Participant’s name, home address and telephone number, date of birth, social security or insurance number or other identification number, salary, nationality, job title(s), any shares of stock held in the Company or any of its subsidiaries and
affiliates, details of all Awards, in each case, for the purpose of implementing, managing and administering the Plan and Awards (the “Data”). The Company and its subsidiaries and affiliates may transfer the Data amongst themselves
as necessary for the purpose of implementation, administration and management of a Participant’s participation in the Plan, and the Company and its subsidiaries and affiliates may each further transfer the Data to any third parties assisting
the Company in the implementation, administration and management of the Plan. These recipients may be located in the Participant’s country, or elsewhere, and the Participant’s country may have different data privacy laws and protections
than the recipients’ country. Through acceptance of an Award, each Participant authorizes such recipients to receive, possess, use, retain and transfer the Data, in electronic or other form, for the purposes of implementing, administering and
managing the Participant’s 

  
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participation in the Plan, including any requisite transfer of such Data as may be required to a broker or other third party with whom the Company or the Participant may elect to deposit any
shares of Common Stock. The Data related to a Participant will be held only as long as is necessary to implement, administer, and manage the Participant’s participation in the Plan. A Participant may, at any time, view the Data held by the
Company with respect to such Participant, request additional information about the storage and processing of the Data with respect to such Participant, recommend any necessary corrections to the Data with respect to the Participant or refuse or
withdraw the consents herein in writing, in any case without cost, by contacting his or her local human resources representative. The Company may cancel Participant’s ability to participate in the Plan and, in the Administrator’s
discretion, the Participant may forfeit any outstanding Awards if the Participant refuses or withdraws his or her consents as described herein. For more information on the consequences of refusal to consent or withdrawal of consent, Participants may
contact their local human resources representative. 
 10.11 Severability. In the event any portion of the Plan or any action taken
pursuant thereto shall be held illegal or invalid for any reason, the illegality or invalidity shall not affect the remaining parts of the Plan, and the Plan shall be construed and enforced as if the illegal or invalid provisions had not been
included, and the illegal or invalid action shall be null and void. 
 10.12 Governing Documents. In the event of any contradiction
between the Plan and any Award Agreement or any other written agreement between a Participant and the Company or any Subsidiary of the Company that has been approved by the Administrator, the terms of the Plan shall govern, unless it is expressly
specified in such Award Agreement or other written document that a specific provision of the Plan shall not apply. 
 10.13
Submission to Jurisdiction; Waiver of Jury Trial. By accepting an Award, each Participant irrevocably and unconditionally consents to submit to the exclusive jurisdiction of the courts of the State of California and of the United
States of America, in each case located in the State of California, for any action arising out of or relating to the Plan (and agrees not to commence any litigation relating thereto except in such courts), and further agrees that service of any
process, summons, notice or document by U.S. registered mail to the address contained in the records of the Company shall be effective service of process for any litigation brought against it in any such court. By accepting an Award, each
Participant irrevocably and unconditionally waives any objection to the laying of venue of any litigation arising out of Plan or Award hereunder in the courts of the State of California or the United States of America, in each case located in the
State of California, and further irrevocably and unconditionally waives and agrees not to plead or claim in any such court that any such litigation brought in any such court has been brought in an inconvenient forum. By accepting an Award, each
Participant irrevocably and unconditionally waives, to the fullest extent permitted by applicable law, any and all rights to trial by jury in connection with any litigation arising out of or relating to the Plan or any Award hereunder. 

10.14 Governing Law. The provisions of the Plan and all Awards made hereunder shall be governed by and interpreted in accordance with
the laws of the State of Delaware, disregarding choice-of-law principles of the law of any state that would require the application of the laws of a jurisdiction other
than such state. 

  
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 10.15 Restrictions on Shares; Claw-back Provisions. Shares of Common Stock
acquired in respect of Awards shall be subject to such terms and conditions as the Administrator shall determine, including, without limitation, restrictions on the transferability of shares of Common Stock, the right of the Company to repurchase
shares of Common Stock, the right of the Company to require that shares of Common Stock be transferred in the event of certain transactions, tag-along rights, bring-along rights, redemption and co-sale rights and voting requirements. Such terms and conditions may be additional to those contained in the Plan and may, as determined by the Administrator, be contained in the applicable Award Agreement or in an
exercise notice, stockholders’ agreement or in such other agreement as the Administrator shall determine, in each case in a form determined by the Administrator. The issuance of such shares of Common Stock shall be conditioned on the
Participant’s consent to such terms and conditions and the Participant’s entering into such agreement or agreements. All Awards (including any proceeds, gains or other economic benefit actually or constructively received by Participant
upon any receipt or exercise of any Award or upon the receipt or resale of any shares of Common Stock underlying the Award) shall be subject to the provisions of any claw-back policy implemented by the Company, including, without limitation, any
claw-back policy adopted to comply with the requirements of the Dodd-Frank Wall Street Reform and Consumer Protection Act and any rules or regulations promulgated thereunder, to the extent set forth in such claw-back policy and/or in the applicable
Award Agreement. 
 10.16 Titles and Headings. The titles and headings of the Sections in the Plan are for convenience of reference
only and, in the event of any conflict, the text of the Plan, rather than such titles or headings, shall control. 
 10.17 Conformity to
Securities Laws. Participant acknowledges that the Plan is intended to conform to the extent necessary with all provisions of the Securities Act and the Exchange Act and any and all regulations and rules promulgated by the Securities and
Exchange Commission thereunder, and state securities laws and regulations. Notwithstanding anything herein to the contrary, the Plan and all Awards granted hereunder shall be administered only in such a manner as to conform to such laws, rules and
regulations. To the extent permitted by Applicable Laws, the Plan and all Award Agreements shall be deemed amended to the extent necessary to conform to such laws, rules and regulations. 

11. Definitions. As used in the Plan, the following words and phrases shall have the following meanings: 

11.1 “Administrator” means the Board or a Committee to the extent that the Board’s powers or authority under the Plan
have been delegated to such Committee. 
 11.2 “Applicable Laws” means the requirements relating to the administration of
equity incentive plans under U.S. federal and state securities, tax and other applicable laws, rules and regulations, the applicable rules of any stock exchange or quotation system on which the Common Stock is listed or quoted and the applicable
laws and rules of any foreign country or other jurisdiction where Awards are granted or issued under the Plan. 
 11.3
“Award” means, individually or collectively, a grant under the Plan of Options, Restricted Stock, Restricted Stock Units or Other Stock-Based Awards. 

  
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 11.4 “Award Agreement” means a written agreement evidencing an Award, which
agreements may be in electronic medium and shall contain such terms and conditions with respect to an Award as the Administrator shall determine, consistent with and subject to the terms and conditions of the Plan. 

11.5 “Board” means the Board of Directors of the Company. 

11.6 “Change in Control” means (i) a merger or consolidation of the Company with or into any other corporation or other
entity or person, (ii) a sale, lease, exchange or other transfer in one transaction or a series of related transactions of all or substantially all of the Company’s assets, or (iii) any other transaction, including the sale by the
Company of new shares of its capital stock or a transfer of existing shares of capital stock of the Company, the result of which is that a third party that is not an affiliate of the Company or its stockholders (or a group of third parties not
affiliated with the Company or its stockholders) immediately prior to such transaction acquires or holds capital stock of the Company representing a majority of the Company’s outstanding voting power immediately following such transaction;
provided that the following events shall not constitute a “Change in Control”: (A) a transaction (other than a sale of all or substantially all of the Company’s assets) in which the holders of the voting securities of
the Company immediately prior to the merger or consolidation hold, directly or indirectly, at least a majority of the voting securities in the successor corporation or its parent immediately after the merger or consolidation; (B) a sale, lease,
exchange or other transaction in one transaction or a series of related transactions of all or substantially all of the Company’s assets to an affiliate of the Company; (C) an initial public offering of any of the Company’s
securities; (D) a reincorporation of the Company solely to change its jurisdiction; or (E) a transaction undertaken for the primary purpose of creating a holding company that will be owned in substantially the same proportion by the
persons who held the Company’s securities immediately before such transaction. Notwithstanding the foregoing, if a Change in Control would give rise to a payment or settlement event with respect to any Award that constitutes “nonqualified
deferred compensation,” the transaction or event constituting the Change in Control must also constitute a “change in control event” (as defined in Treasury Regulation §1.409A-3(i)(5)) in
order to give rise to the payment or settlement event for such Award, to the extent required by Section 409A. 
 11.7
“Code” means the Internal Revenue Code of 1986, as amended, and the regulations issued thereunder. 
 11.8
“Committee” means one or more committees or subcommittees of the Board, which may be comprised of one or more directors and/or executive officers of the Company, in either case, to the extent permitted in accordance with Applicable
Laws. 
 11.9 “Common Stock” means the common stock of the Company.  

11.10 “Company” means Biomea Fusion, Inc., a Delaware corporation, or any successor thereto. Except where the context
otherwise requires, the term “Company” includes any of the Company’s present or future parent or subsidiary corporations as defined in Sections 424(e) or (f) of the Code and any other business venture (including, without
limitation, joint venture or limited liability company) in which the Company has a significant interest, as determined by the Administrator. 

  
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 11.11 “Consultant” means any person, including any advisor, engaged
by the Company or a parent or subsidiary of the Company to render services to such entity if: (i) the consultant or adviser renders bona fide services to the Company; (ii) the services rendered by the consultant or advisor are not
in connection with the offer or sale of securities in a capital-raising transaction and do not directly or indirectly promote or maintain a market for the Company’s securities; and (iii) the consultant or advisor is a natural person, or
such other advisor or consultant as is approved by the Administrator. 
 11.12 “Conversion Common Stock” shall mean the
93,262 shares of Common Stock issued to certain employees and consultants of the Company in exchange for units held by such individuals (which units had been issued upon the conversion of incentive units of the Company or its affiliates) in
connection with the conversion of the Company from a limited liability company to a corporation. 
 11.13 “Designated
Beneficiary” means the beneficiary or beneficiaries designated, in a manner determined by the Administrator, by a Participant to receive amounts due or exercise rights of the Participant in the event of the Participant’s death
or incapacity In the absence of an effective designation by a Participant, “Designated Beneficiary” shall mean the Participant’s estate. 

11.14 “Director” means a member of the Board. 

11.15 “Disability” means a permanent and total disability within the meaning of Section 22(e)(3) of the Code, as it may
be amended from time to time. 
 11.16 “Dividend Equivalents” means a right granted to a Participant pursuant to
Section 6.4(c) hereof to receive the equivalent value (in cash or shares of Common Stock) of dividends paid on shares of Common Stock. 

11.17 “Employee” means any person, including officers and Directors, employed by the Company (within the meaning of
Section 3401(c) of the Code) or any parent or subsidiary of the Company. 
 11.18 “Equity Restructuring” means, as
determined by the Administrator, a non-reciprocal transaction between the Company and its stockholders, such as a stock dividend, stock split, spin-off or
recapitalization through a large, nonrecurring cash dividend, that affects the shares of Common Stock (or other securities of the Company) or the share price of Common Stock (or other securities of the Company) and causes a change in the per share
value of the Common Stock underlying outstanding Awards. 
 11.19 “Exchange Act” means the Securities Exchange Act of 1934,
as amended. 
 11.20 “Fair Market Value” means, as of any date, the value of Stock determined as follows: (i) if the
Common Stock is listed on any established stock exchange, its Fair Market Value shall be the closing sales price for such Common Stock as quoted on such exchange for such date, or if no sale occurred on such date, the first market trading day
immediately prior to such date during which a sale occurred, as reported in The Wall Street Journal or such other source as the Administrator deems reliable; (ii) if the Common Stock is not traded on a stock exchange but


  
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is quoted on a national market or other quotation system, the last sales price on such date, or if no sales occurred on such date, then on the date immediately prior to such date on which sales
prices are reported, as reported in The Wall Street Journal or such other source as the Administrator deems reliable; or (iii) in the absence of an established market for the Common Stock, the Fair Market Value thereof shall be
determined by the Administrator in its sole discretion. 
 11.21 “Incentive Stock Option” means an “incentive stock
option” as defined in Section 422 of the Code. 
 11.22 “Non-Qualified Stock
Option” means an Option that is not intended to be or otherwise does not qualify as an Incentive Stock Option. 
 11.23
“Option” means an option to purchase Common Stock. 
 11.24 “Other Stock-Based Awards” means other Awards
of shares of Common Stock, and other Awards that are valued in whole or in part by reference to, or are otherwise based on, shares of Common Stock or other property. 

11.25 “Participant” means a Service Provider who has been granted an Award under the Plan. 

11.26 “Plan” means this 2020 Equity Incentive Plan. 

11.27 “Publicly Listed Company” means that the Company or its successor (i) is required to file periodic reports pursuant
to Section 12 of the Exchange Act and (ii) the Common Stock is listed on one or more National Securities Exchanges (within the meaning of the Exchange Act) or is quoted on NASDAQ or a successor quotation system. 

11.28 “Restricted Stock” means Common Stock awarded to a Participant pursuant to Section 6 hereof that is subject to
certain vesting conditions and other restrictions. 
 11.29 “Restricted Stock Unit” means an unfunded, unsecured right to
receive, on the applicable settlement date, one share of Common Stock or an amount in cash or other consideration determined by the Administrator equal to the value thereof as of such payment date, which right may be subject to certain vesting
conditions and other restrictions. 
 11.30 “Section 409A” means Section 409A of the Code and all
regulations, guidance, compliance programs and other interpretative authority thereunder. 
 11.31 “Securities Act” means
the Securities Act of 1933, as amended from time to time. 
 11.32 “Service Provider” means an Employee, Consultant or
Director. 
 11.33 “Termination of Service” means the date the Participant ceases to be a Service Provider. 

* * * * * 

  
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 BIOMEA FUSION, INC. 

2020 EQUITY INCENTIVE PLAN  

CALIFORNIA SUPPLEMENT 

This supplement is intended to satisfy the requirements of Section 25102(o) of the California Corporations Code and the regulations
issued thereunder (“Section 25102(o)”). Notwithstanding anything to the contrary contained in the Plan and except as otherwise determined by the Administrator, the provisions set forth in this supplement shall
apply to all Awards granted under the Plan to a Participant who is a resident of the State of California on the date of grant (a “California Participant”) and which are intended to be exempt from registration in California pursuant
to Section 25102(o), and otherwise to the extent required to comply with applicable law (but only to such extent). Definitions in the Plan are applicable to this supplement. 

1. Limitation On Securities Issuable Under Plan. The amount of securities issued pursuant to the Plan shall not exceed the amounts
permitted under Section 260.140.45 of the California code of regulations to the extent applicable. 
 2. Additional Limitations For
Grants. The terms of all Awards shall comply, to the extent applicable, with Sections 260.140.41 and 260.140.42 of the California Code of Regulations. 

3. Additional Requirement To Provide Information To California Participants. The Company shall provide to each California
Participant, not less frequently than annually, copies of annual financial statements (which need not be audited). The Company shall not be required to provide such statements to key persons whose duties in connection with the Company assure their
access to equivalent information. In addition, this information requirement shall not apply to any plan or agreement that complies with all conditions of Rule 701 of the Securities Act (“Rule 701”); provided that for
purposes of determining such compliance, any registered domestic partner shall be considered a “family member” as that term is defined in Rule 701. 

* * * * * 

  
 CS-1