Document:

EX-10.2

 Exhibit 10.2 

KEROS THERAPEUTICS, INC. 
 2017
STOCK INCENTIVE PLAN 
 1. Purpose 

The purpose of this 2017 Stock Incentive Plan (the “Plan”) of Keros Therapeutics, Inc., a Delaware corporation (the
“Company”), is to advance the interests of the Company’s stockholders by enhancing the Company’s ability to attract, retain and motivate persons who are expected to make important contributions to the Company and by providing
such persons with equity ownership opportunities and performance-based incentives that are intended to better align the interests of such persons with those of the Company’s stockholders. Except where the context otherwise requires, the term
“Company” shall include any of the Company’s present or future parent or subsidiary corporations as defined in Sections 424(e) or (f) of the Internal Revenue Code of 1986, as amended, and any regulations promulgated thereunder
(the “Code”) and any other business venture (including, without limitation, joint venture or limited liability company) in which the Company has a controlling interest, as determined by the Board of Directors of the Company (the
“Board”). 
 2. Eligibility 

All of the Company’s employees, officers, directors, consultants and advisors are eligible to be granted options, restricted stock,
restricted stock units (“RSUs”) and other stock-based awards (each, an “Award”) under the Plan. Each person who receives an Award under the Plan is deemed a “Participant”. 

3. Administration and Delegation 
 (a)
Administration by Board of Directors. The Plan will be administered by the Board. The Board shall have authority to grant Awards and to adopt, amend and repeal such administrative rules, guidelines and practices relating to the Plan as it
shall deem advisable. The Board may construe and interpret the terms of the Plan and any Award agreements entered into under the Plan. The Board may correct any defect, supply any omission or reconcile any inconsistency in the Plan or any Award in
the manner and to the extent it shall deem expedient to carry the Plan into effect and it shall be the sole and final judge of such expediency. All decisions by the Board shall be made in the Board’s sole discretion and shall be final and
binding on all persons having or claiming any interest in the Plan or in any Award. No director or person acting pursuant to the authority delegated by the Board shall be liable for any action or determination relating to or under the Plan made in
good faith. 
 (b) Appointment of Committees. To the extent permitted by applicable law, the Board may delegate any or all of its
powers under the Plan to one or more committees or subcommittees of the Board (a “Committee”). All references in the Plan to the “Board” shall mean the Board or a Committee of the Board or the officers referred to in
Section 3(c) to the extent that the Board’s powers or authority under the Plan have been delegated to such Committee or officers. 

  
 1. 

 (c) Delegation to Officers. To the extent permitted by applicable law, the Board may
delegate to one or more officers of the Company the power to grant Awards (subject to any limitations under the Plan) to employees or officers of the Company or any of its present or future subsidiary corporations and to exercise such other powers
under the Plan as the Board may determine, provided that the Board shall fix the terms of the Awards to be granted by such officers (including the exercise price of such Awards, which may include a formula by which the exercise price will be
determined) and the maximum number of shares subject to Awards that the officers may grant; provided further, however, that no officer shall be authorized to grant Awards to any “executive officer” of the Company (as defined by Rule 3b-7 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”)) or to any “officer” of the Company (as defined by Rule 16a-1 under the
Exchange Act). 
 4. Stock Available for Awards. 

(a) Number of Shares. Subject to adjustment under Section 8, Awards may be made under the Plan for up to 518,11011 shares of common stock, $0.0001 par value per share, of the Company (the “Common Stock”). If any Award expires or is terminated, surrendered or canceled without having been fully exercised,
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 the original issuance price pursuant to a contractual repurchase right), or results in any Common Stock not
being issued, 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 tendered to the Company by a Participant to exercise an Award 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 issued under
the Plan may consist in whole or in part of authorized but unissued shares or treasury shares. At no time while there is any Option (as defined below) outstanding and held by a Participant who was a resident of the State of California on the date of
grant of such Option, shall the total number of shares of Common Stock issuable upon exercise of all outstanding options and the total number of shares provided for under any stock bonus or similar plan or agreement of the Company exceed the
applicable percentage as calculated in accordance with the conditions and exclusions of Section 260.140.45 of the California Code of Regulations (the “California Regulations”), based on the shares of the Company which are outstanding
at the time the calculation is made. 
  
  

	1	 Increased by 982,533 shares, from 518,110 shares to 1,500,643 shares, pursuant to Board action taken on
December 18, 2017. 

 Increased by 442,000 shares, from 1,500,643 shares to 1,942,643 shares, pursuant to Board action
taken on January 2, 2018. 
 1,424,533 share increase (inclusive of December 18, 2017 and January 2, 2018 board approved
increases) ratified by stockholder consent on January 2, 2018. 
 Increased by 80,000 shares, from 1,942,643 to 2,022,643 shares,
pursuant to Board action taken on October 9, 2018 and later stockholder ratification. 
 Increased by 933,500 shares, from 2,022,643 to
2,956,143 shares, pursuant to Board action taken on March 4, 2019 (subject to delivery of requisite stockholder approval). 

  
 2. 

 (b) 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 Board may grant Awards in substitution for any options or other stock or stock-based awards granted by such entity or an affiliate thereof. Substitute Awards may be
granted on such terms as the Board 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(a), except as
may be required by reason of Section 422 and related provisions of the Code. 
 5. Stock Options 

(a) General. The Board may grant options to purchase Common Stock (each, an “Option”) and 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 federal or state securities laws, as it considers
necessary or advisable. An Option that is not intended to be an Incentive Stock Option (as hereinafter defined) shall be designated a “Nonstatutory Stock Option”. 

(b) Incentive Stock Options. An Option that the Board intends to be an “incentive stock option” as defined in
Section 422 of the Code (an “Incentive Stock Option”) shall only be granted to employees of the Company, 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 entities the employees of which are eligible to receive Incentive Stock Options under the Code. The Option shall be subject to and shall be construed consistently with the requirements of Section 422 of the Code, and without
limiting generality of the foregoing, the Option shall be deemed to include terms that comply with the eligibility standards described section 422(b) of the Code. Subject to the remaining provisions of this Section 5(b), if an Option intended
to qualify as an Incentive Stock Option does not so qualify, the Board may, at its discretion, amend the Plan and Award with respect to such Option so that such Option qualifies as an Incentive Stock Option. To the extent that the aggregate Fair
Market Value (determined at the time of grant) of Common Stock with respect to which Incentive Stock Options are exercisable for the first time by any Participant during any calendar year (under all plans of the Company and any affiliates) exceeds
$100,000 (or such other limit established in the Code) or otherwise does not comply with the rules governing Incentive Stock Options, the Options or portions thereof that exceed such limit (according to the order in which they were granted) or
otherwise do not comply with the rules will be treated as Nonstatutory Stock Options, notwithstanding any contrary provision of the applicable Award. The Company shall have no liability to a Participant, or any other party, if an Option (or any part
thereof) that is intended to be an Incentive Stock Option is not an Incentive Stock Option or for any action taken by the Board, including without limitation the conversion of an Incentive Stock Option to a Nonstatutory Stock Option. 

(c) Exercise Price. The Board shall establish the exercise price of each Option and specify the exercise price in the applicable option
agreement. 
 (d) Duration of Options. Each Option shall be exercisable at such times and subject to such terms and conditions as the
Board may specify in the applicable option agreement. 

  
 3. 

 (e) Exercise of Option. Options may be exercised by delivery to the Company of a
written notice of exercise signed by the proper person or by any other form of notice (including electronic notice) approved by the Board together with payment in full as specified in Section 5(f) for the number of shares for which the Option
is exercised. Shares of Common Stock subject to the Option will be delivered by the Company as soon as practicable following exercise. 

(f) Payment Upon Exercise. Common Stock purchased upon the exercise of an Option granted under the Plan shall be paid for as follows:

 (1) in cash or by check, payable to the order of the Company; 

(2) when the Common Stock is registered under the Exchange Act, except as may otherwise be provided in the applicable option agreement, by
(i) delivery of an irrevocable and unconditional undertaking by a creditworthy broker to deliver promptly to the Company sufficient funds to pay the exercise price and any required tax withholding or (ii) delivery by the Participant to the
Company of a copy of irrevocable and unconditional instructions to a creditworthy broker to deliver promptly to the Company cash or a check sufficient to pay the exercise price and any required tax withholding; 

(3) when the Common Stock is registered under the Exchange Act and to the extent provided for in the applicable option agreement or approved
by the Board, in its sole discretion, by delivery (either by actual delivery or attestation) of shares of Common Stock owned by the Participant valued at their fair market value as determined by (or in a manner approved by) the Board (“Fair
Market Value”), provided (i) such method of payment is then permitted under applicable law, (ii) 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 Board in its discretion and (iii) such Common Stock is not subject to any repurchase, forfeiture, unfulfilled vesting or other similar requirements; 

(4) to the extent permitted by applicable law and provided for in the applicable option agreement or approved by the Board, in its sole
discretion, by (i) delivery of a promissory note of the Participant to the Company on terms determined by the Board, or (ii) payment of such other lawful consideration as the Board may determine; or 

(5) by any combination of the above permitted forms of payment. 

6. Restricted Stock; Restricted Stock Units 

(a) General. The Board may grant Awards entitling recipients to acquire shares of Common Stock (“Restricted Stock”), 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 (or to require forfeiture of such shares if issued at no cost) from the recipient in the event that conditions specified by
the Board in the applicable Award are not satisfied prior to the end of the applicable restriction period or periods established by the Board for such Award. Instead of granting Awards for Restricted Stock, the Board may grant Awards entitling the
recipient to receive shares of Common Stock or cash to be delivered at the time such Award vests (“Restricted Stock Units”) (Restricted Stock and Restricted Stock Units are each referred to herein as a “Restricted Stock Award”).

  
 4. 

 (b) Terms and Conditions for All Restricted Stock Awards. The Board shall determine
the terms and conditions of a Restricted Stock Award, including the conditions for vesting and repurchase (or forfeiture) and the issue price, if any. 

(c) Additional Provisions Relating to Restricted Stock. 

(1) Dividends. Participants holding shares of Restricted Stock will be entitled to all ordinary cash dividends paid with respect to
such shares, unless otherwise provided by the Board. Unless otherwise provided by the Board, if any dividends or distributions are paid in shares, or consist of a dividend or distribution to holders of Common Stock other than an ordinary cash
dividend, the shares, cash 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 no later than the
end of the calendar year in which the dividends are paid to shareholders of that class of stock or, if later, the 15th day of the third month following the date the dividends are paid to shareholders of that class of stock. 

(2) Stock Certificates. The Company may require that any stock certificates issued in respect of shares of Restricted Stock shall be
deposited in escrow by the Participant, together with a stock power endorsed in blank, with the Company (or its designee). At the expiration of the applicable restriction periods, the Company (or such designee) shall deliver the certificates no
longer subject to such restrictions to the Participant or if the Participant has died, to the beneficiary designated, in a manner determined by the Board, by a Participant to receive amounts due or exercise rights of the Participant in the event of
the Participant’s death (the “Designated Beneficiary”). In the absence of an effective designation by a Participant, “Designated Beneficiary” shall mean the Participant’s estate. 

7. Other Stock-Based Awards 
 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, may be granted hereunder to Participants (“Other Stock-Based
Awards”), including without limitation stock appreciation rights (“SARs”) and Awards entitling recipients 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 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 or cash, as the Board shall
determine. Subject to the provisions of the Plan, the Board shall determine the terms and conditions of each Other Stock-Based Award, including any purchase price applicable thereto. 

8. Adjustments for Changes in Common Stock and Certain Other 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 

  
 5. 

 
available under this Plan, (ii) the number and class of securities and exercise price per share of each outstanding Option, (iii) the number of shares subject to and the repurchase
price per share subject to each outstanding Restricted Stock Award, and (iv) the terms of each other outstanding Award shall be equitably adjusted by the Company (or substituted Awards may be made, if applicable) in the manner determined by the
Board; provided that, unless otherwise determined by the Board, such changes to the Options shall comply with section 1.424-1 of the Treasury Regulations. Without limiting the generality of the foregoing, in
the event the Company effects a split of the Common Stock by means of a stock dividend and the exercise price of and the number of shares subject to an outstanding Option are adjusted as of the date of the distribution of the dividend (rather than
as of the record date for such dividend), then an optionee who exercises an Option between the record date and the distribution date for such stock dividend shall be entitled to receive, on the distribution date, the stock dividend with respect to
the shares of Common Stock acquired upon such Option exercise, notwithstanding the fact that such shares were not outstanding as of the close of business on the record date for such stock dividend. 

(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 exchange of all of the Common Stock of the Company for cash,
securities or other property pursuant to a share exchange transaction or (c) any liquidation or dissolution of the Company. 
 (2)
Consequences of a Reorganization Event on Awards Other than Restricted Stock Awards. In connection with a Reorganization Event, the Board may take any one or more of the following actions as to all or any (or any portion of) outstanding
Awards other than Restricted Stock Awards on such terms as the Board determines: (i) provide that Awards shall be assumed, or substantially equivalent Awards shall be substituted, by the acquiring or succeeding corporation (or an affiliate
thereof); provided that, unless otherwise determined by the Board, such assumption or substitution of the Options shall comply with section 1.424-1 of the Treasury Regulations, (ii) upon written notice to
a Participant, provide that the Participant’s unexercised Awards will terminate immediately prior to the consummation of such Reorganization Event unless exercised by the Participant within a specified period following the date of such notice,
(iii) provide that outstanding Awards shall become exercisable, realizable, or deliverable, or restrictions applicable to an Award shall lapse, in whole or in part prior to or upon such Reorganization Event, (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”), make or provide for a cash
payment to a Participant equal to the excess, if any, of (A) the Acquisition Price times the number of shares of Common Stock subject to the Participant’s Awards (to the extent the exercise price does not exceed the Acquisition Price) over
(B) the aggregate exercise price of all such outstanding Awards and any applicable tax withholdings, in exchange for the termination of such Awards, (v) provide that, in connection with a liquidation or dissolution of the Company, Awards
shall convert into the right to receive liquidation proceeds (if applicable, net of the exercise price thereof and any applicable tax withholdings) and (vi) any combination of the foregoing. In taking any of the actions permitted under this
Section 8(b), the Board shall not be obligated by the Plan to treat all Awards, all Awards held by a Participant, or all Awards of the same type, identically. 

  
 6. 

 For purposes of clause (i) above, an Option shall be considered assumed if, following
consummation of the Reorganization Event, the 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 common stock
of the acquiring or succeeding corporation (or an affiliate thereof) equivalent in value (as determined by the Board) to the per share consideration received by holders of outstanding shares of Common Stock as a result of the Reorganization Event.

 (3) Consequences of a Reorganization Event on Restricted Stock Awards. Upon the occurrence of a Reorganization Event other than a
liquidation or dissolution of the Company, the repurchase and other rights of the Company under each outstanding Restricted Stock Award shall inure to the benefit of the Company’s successor and shall, unless the Board determines otherwise,
apply to the cash, securities or other property which the Common Stock was converted into or exchanged for pursuant to such Reorganization Event in the same manner and to the same extent as they applied to the Common Stock subject to such Restricted
Stock Award. Upon the occurrence of a Reorganization Event involving the liquidation or dissolution of the Company, except to the extent specifically provided to the contrary in the instrument evidencing any Restricted Stock Award or any other
agreement between a Participant and the Company, all restrictions and conditions on all Restricted Stock Awards then outstanding shall automatically be deemed terminated or satisfied. 

9. General Provisions Applicable to Awards 

(a) Transferability of Awards. Except as the Board may otherwise determine or provide in an Award, 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 or, other than in the case of an Incentive Stock Option, pursuant
to a qualified domestic relations order, 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.

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

  
 7. 

 (c) Board 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 need not be identical, and the Board need not treat Participants uniformly. 

(d) Termination of Status. The Board shall determine the effect on an Award of the disability, death, termination or other cessation of
employment, authorized leave of absence or other change in the employment or other status of a Participant and the extent to which, and the period during which, the Participant, or the Participant’s legal representative, conservator, guardian
or Designated Beneficiary, may exercise rights under the Award. 
 (e) Withholding. The Company shall not be obligated to deliver
certificates, release from forfeiture, otherwise recognize a Participant’s unrestricted ownership in an Award or the cash or property proceeds therefrom, until the Company satisfies all applicable federal, state, and local or other income and
employment tax withholding obligations. In its sole discretion, the Company may satisfy such withholding obligations by any of the following means or by a combination of such means: (i) causing the Participant to tender to the Company cash
payment; (ii) withholding cash from an Award settled in cash; (iii) withholding from amounts otherwise payable by the Company to the Participant, including but not limited to additional withholding on the Participant’s salary or
wages, or from proceeds from the sale of Common Stock issued pursuant to an Award; (iv) delivery of shares of Common Stock, including shares retained from the Award creating the tax obligation, valued at their Fair Market Value; provided,
however, except as otherwise provided by the Board, that the total tax withholding where stock is being used to satisfy such tax obligations cannot exceed the Company’s minimum statutory withholding obligations (based on minimum statutory
withholding rates for federal and state tax purposes, including payroll taxes, that are applicable to such supplemental taxable income), and provided, further, shares surrendered to satisfy tax withholding requirements cannot be subject to any
repurchase, forfeiture, unfulfilled vesting or other similar requirements; or (v) by such other method as determined by the Board. 

(f) Amendment of Award. 

(1) The Board 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 realization, and converting an Incentive Stock Option to a Nonstatutory Stock Option. The Participant’s consent to such action shall be required unless (i) the Board determines
that the action, taking into account any related action, would not materially and adversely affect the Participant’s rights under the Plan, (ii) the change is permitted under Section 8 hereof, or (iii) the change is to ensure
that an Option intended to qualify as an Incentive Stock Option qualifies as such. 
 (2) The Board may, without stockholder approval, amend
any outstanding Award granted under the Plan to provide an exercise price per share that is lower than the then- current exercise price per share of such outstanding Award. The Board may also, without stockholder approval, cancel any outstanding
award (whether or not granted under the Plan) and grant in substitution therefor new Awards under the Plan covering the same or a different number of shares of Common Stock and having an exercise price per share lower than the then- current exercise
price per share of the cancelled award. 

  
 8. 

 (g) 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 Company may consider appropriate to satisfy the requirements of any applicable laws, rules or regulations. 

(h) Acceleration. The Board may at any time provide that any Award shall become immediately 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 

(a) 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, except as expressly provided in the applicable Award. 
 (b) No Rights As
Stockholder. Subject to the provisions of the applicable Award, 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. 
 (c) 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 expiration of 10 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. 
 (d) Amendment of Plan. The Board may amend, suspend or
terminate the Plan or any portion thereof at any time; provided that if at any time the approval of the Company’s stockholders is required as to any modification or amendment under Section 422 of the Code or any successor provision with
respect to Incentive Stock Options, the Board may not effect such modification or amendment without such approval. Unless otherwise specified in the amendment, any amendment to the Plan adopted in accordance with this Section 10(d) shall apply
to, and be binding on the holders of, all Awards outstanding under the Plan at the time the amendment is adopted, provided the Board determines that such amendment does not materially and adversely affect the rights of Participants under the Plan.

  
 9. 

 (e) Authorization of Sub-Plans. The Board may
from time to time establish one or more sub-plans under the Plan for purposes of satisfying applicable blue sky, securities or tax laws of various jurisdictions. The Board shall establish such sub-plans by adopting supplements to this Plan containing (i) such limitations on the Board’s discretion under the Plan as the Board deems necessary or desirable or (ii) such additional terms and
conditions not otherwise inconsistent with the Plan as the Board shall deem necessary or desirable. All supplements adopted by the Board shall be deemed to be part of the Plan, but each supplement shall apply only to Participants within the affected
jurisdiction and the Company shall not be required to provide copies of any supplement to Participants in any jurisdiction which is not the subject of such supplement. 

(f) Compliance with Code Section 409A. Unless otherwise expressly provided for in an Award, the Plan and Award will
be interpreted to the greatest extent possible in a manner that makes the Plan and the Awards granted hereunder exempt from Section 409A of the Code, and, to the extent not so exempt, in compliance with Section 409A of the Code. If the
Board determines that any Award granted hereunder is not exempt from and is therefore subject to Section 409A of the Code, the Award will incorporate the terms and conditions necessary to avoid the consequences specified in
Section 409A(a)(1) of the Code, and to the extent an Award is silent on terms necessary for compliance, such terms as deemed necessary by the Board in its sole discretion are hereby incorporated by reference into the Award. Without limiting the
generality of the foregoing, if shares of Common Stock are publicly traded, and if a Participant holding an Award that constitutes “deferred compensation” under Section 409A of the Code is a “specified employee” for purposes
of Section 409A of the Code, no distribution or payment of any amount that is due because of a “separation from service” (as defined in Section 409A of the Code without regard to alternative definitions thereunder) will be issued
or paid before the date that is six (6) months following the date of such Participant’s “separation from service” or, if earlier, the date of the Participant’s death, unless such distribution or payment can be made in a
manner that complies with Section 409A of the Code, and any amounts so deferred will be paid in a lump sum on the day after such six (6) month period elapses, with the balance paid thereafter on the original schedule. The Company shall
have no liability to a Participant, or any other party, if an Award that is intended to be exempt from, or compliant with, Section 409A of the Code is not so exempt or compliant or for any other action taken by the Board. 

(g) 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, excluding choice-of-law principles of the law of such state that would require the application of the laws of a jurisdiction other than
such state. 

  
 10. 

 KEROS THERAPEUTICS, INC. 

2017 STOCK INCENTIVE PLAN 

CALIFORNIA SUPPLEMENT 
 Pursuant
to Section 10(e) of the Plan, the Board has adopted this supplement for purposes of satisfying the requirements of Section 25102(o) of the California Law: 

Any 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”) shall be subject to the following additional limitations, terms and conditions: 
 1. Additional Limitations on Options. 

(a) Minimum Vesting Rate. Except in the case of Options granted to California Participants who are officers, directors, managers,
consultants or advisors of the Company or its affiliates (which Options may become exercisable at whatever rate is determined by the Board), Options granted to California Participants shall become exercisable at a rate of not less than 20% per year
over five years from the date of grant; provided, that, such Options may be subject to such reasonable forfeiture conditions as the Board may choose to impose and which are not inconsistent with Section 260.140.41 of the
California Regulations. 
 (b) Minimum Exercise Price. The exercise price of Options granted to California Participants may not be
less than 85% of the Fair Market Value of the Common Stock on the date of grant in the case of a Nonstatutory Stock Option or less than 100% of the Fair Market Value of the Common Stock on the date of grant in the case of an Incentive Stock Option;
provided, however, that if the California Participant is a person who owns stock possessing more than 10% of the total combined voting power of all classes of stock of the Company or its parent or subsidiary corporations, the exercise
price shall be not less than 110% of the Fair Market Value of the Common Stock on the date of grant. 
 (c) Maximum Duration of
Options. No Options granted to California Participants shall have a term in excess of 10 years measured from the Option grant date. 

(d) Minimum Exercise Period Following Termination. Unless a California Participant’s employment is terminated for cause (as
defined by applicable law, the terms of any contract of employment between the Company and such Participant, or in the instrument evidencing the grant of such Participant’s Option), in the event of termination of employment of such Participant,
such Participant shall have the right to exercise an Option, to the extent that he or she was otherwise entitled to exercise such Option on the date employment terminated, as follows: (i) at least six months from the date of termination, if
termination was caused by such Participant’s death or “permanent and total disability” (within the meaning of Section 22(e)(3) of the Code) and (ii) at least 30 days from the date of termination, if termination was caused
other than by such Participant’s death or “permanent and total disability” (within the meaning of Section 22(e)(3) of the Code). 

  
 A - 1 

 (e) Limitation on Repurchase Rights. If an Option granted to a California Participant
gives the Company the right to repurchase shares of Common Stock issued pursuant to the Plan upon termination of employment of such Participant, the terms of such repurchase right must comply with Section 260.140.41(k) of the California
Regulations. 
 2. Additional Limitations for Restricted Stock Awards. 

(a) Minimum Purchase Price. The purchase price for a Restricted Stock Award granted to a California Participant shall be not less than
85% of the Fair Market Value of the Common Stock at the time such Participant is granted the right to purchase shares under the Plan or at the time the purchase is consummated; provided, however, that if such Participant is a person who owns stock
possessing more than 10% of the total combined voting power or value of all classes of stock of the Company or its parent or subsidiary corporations, the purchase price shall be not less than 100% of the Fair Market Value of the Common Stock at the
time such Participant is granted the right to purchase shares under the Plan or at the time the purchase is consummated. 
 (b)
Limitation of Repurchase Rights. If a Restricted Stock Award granted to a California Participant gives the Company the right to repurchase shares of Common Stock issued pursuant to the Plan upon termination of employment of such Participant,
the terms of such repurchase right must comply with Section 260.140.42(h) of the California Regulations. 
 3. Additional Limitations for Other
Stock-Based Awards. The terms of all Awards granted to a California Participant under Section 7 of the Plan shall comply, to the extent applicable, with Section 260.140.41 or Section 260.140.42 of the California Regulations. 

4. Additional Requirement to Provide Information to California Participants. The Company shall provide to each California Participant and to each
California Participant who acquires Common Stock pursuant to the Plan, 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
employees whose duties in connection with the Company assure their access to equivalent information. 
 5. Additional Limitations on Timing of
Awards. No Award granted to a California Participant shall become exercisable, vested or realizable, as applicable to such Award, unless the Plan has been approved by the holders of a majority of the Company’s outstanding voting securities
within 12 months before or after the date the Plan was adopted by the Board. 
 6. Additional Limitations Relating to Definition of Fair Market
Value. For purposes of Section 1(b) and 2(a) of this supplement, “Fair Market Value” shall be determined in a manner not inconsistent with Section 260.140.50 of the California Regulations. 

7. Additional Restriction Regarding Recapitalizations, Stock Splits, Etc. For purposes of Section 8 of the Plan, in the event of a stock split,
reverse stock split, stock dividend, recapitalization, combination, reclassification or other distribution of the Company’s securities, the number of securities allocated to each California Participant must be adjusted proportionately and
without the receipt by the Company of any consideration from any California Participant. 

  
 A - 2EX-10.3

 Exhibit 10.3 

KEROS THERAPEUTICS, INC. 
 Incentive
Stock Option Agreement 
 Granted Under 2017 Stock Incentive Plan 

1. Grant of Option. 
 This agreement
evidences the grant by Keros Therapeutics, Inc., a Delaware corporation (the “Company”) on the “Grant date” (as set forth in the Carta Electronic Notice that is delivered electronically concurrent with this agreement (the
“Carta Notice”)) to the Participant named in the Carta Notice, an employee, consultant or director of the Company, of an option to purchase, in whole or in part, at a per share “Exercise price” (as set forth in the Carta Notice),
on the terms provided herein and in the Company’s 2017 Stock Incentive Plan (the “Plan”), that number of shares (the “Shares”) of common stock, $0.0001 par value per share, of the Company (the “Common Stock”) as
set forth on the Carta Notice. Unless earlier terminated, this option shall expire at 5:00 p.m., Eastern time, on the 10-year anniversary of the Grant date (the “Final Exercise Date”). 

It is intended that the option evidenced by this agreement shall be an incentive stock option as defined in Section 422 of the Internal
Revenue Code of 1986, as amended, and any regulations promulgated thereunder (the “Code”). Except as otherwise indicated by the context, the term “Participant”, as used in this option, shall be deemed to include any person who
acquires the right to exercise this option validly under its terms. 
 2. Vesting Schedule. 

This option will become exercisable (“vest”) as provided in the Carta Notice. 

The right of exercise shall be cumulative so that to the extent the option is not exercised in any period to the maximum extent permissible it
shall continue to be exercisable, in whole or in part, with respect to all Shares for which it is vested until the earlier of the Final Exercise Date or the termination of this option under Section 3 hereof or the Plan. 

3. Exercise of Option. 
 (a) Form of
Exercise. Each election to exercise this option shall be accompanied by a completed Notice of Stock Option Exercise in the form attached hereto as Exhibit A, signed by the Participant, and received by the Company at its principal office,
accompanied by this agreement, and payment in full in the manner provided in the Plan. The Participant may purchase less than the number of Shares covered hereby, provided that no partial exercise of this option may be for any fractional share or
for fewer than ten whole shares. 
 (b) Continuous Relationship with the Company Required. Except as otherwise provided in this
Section 3, this option may not be exercised unless the Participant, at the time he or she exercises this option, is, and has been at all times since the Grant date (as set forth in the Carta Notice), an employee or officer of, or consultant or
advisor to, the Company or any parent or subsidiary of the Company as defined in Section 424(e) or (0 of the Code (an “Eligible Participant”). 

 (c) Termination of Relationship with the Company. If the Participant ceases to
be an Eligible Participant for any reason, then, except as provided in paragraphs (d) and (e) below, the right to exercise this option shall terminate three months after such cessation (but in no event after the Final Exercise Date),
provided that this option shall be exercisable only to the extent that the Participant was entitled to exercise this option on the date of such cessation. Notwithstanding the foregoing, if the Participant, prior to the Final Exercise
Date, violates the non-competition or confidentiality provisions of any employment contract, confidentiality and nondisclosure agreement or other agreement between the Participant and the Company, the right to
exercise this option shall terminate immediately upon such violation. 
 (d) Exercise Period Upon Death or Disability. If the
Participant dies or becomes disabled (within the meaning of Section 22(e)(3) of the Code) prior to the Final Exercise Date while he or she is an Eligible Participant and the Company has not terminated such relationship for “cause” as
specified in paragraph (e) below, this option shall be exercisable, within the period of one year following the date of death or disability of the Participant, by the Participant (or in the case of death by an authorized transferee),
provided that this option shall be exercisable only to the extent that this option was exercisable by the Participant on the date of his or her death or disability, and further provided that this option shall not be exercisable after
the Final Exercise Date. 
 (e) Termination for Cause. If, prior to the Final Exercise Date, the Participant’s employment is
terminated by the Company for Cause (as defined below), the right to exercise this option shall terminate immediately upon the effective date of such termination of employment. If, prior to the Final Exercise Date, the Participant is given notice by
the Company of the termination of his or her employment by the Company for Cause, and the effective date of such employment termination is subsequent to the date of delivery of such notice, the right to exercise this option shall be suspended from
the time of the delivery of such notice until the earlier of (i) such time as it is determined or otherwise agreed that the Participant’s employment shall not be terminated for Cause as provided in such notice or (ii) the effective
date of such termination of employment (in which case the right to exercise this option shall, pursuant to the preceding sentence, terminate upon the effective date of such termination of employment). If the Participant is party to an employment or
severance agreement with the Company that contains a definition of “cause” for termination of employment, “Cause” shall have the meaning ascribed to such term in such agreement. Otherwise, “Cause” shall mean willful
misconduct by the Participant or willful failure by the Participant to perform his or her responsibilities to the Company (including, without limitation, breach by the Participant of any provision of any employment, consulting, advisory,
nondisclosure, non-competition or other similar agreement between the Participant and the Company), as determined by the Company, which determination shall be conclusive. The Participant’s employment
shall be considered to have been terminated for Cause if the Company determines, within 30 days after the Participant’s resignation, that termination for Cause was warranted. 

4. Company Right of First Refusal. 
 (a)
Notice of Proposed Transfer. If the Participant proposes to sell, assign, transfer, pledge, hypothecate or otherwise dispose of, by operation of law or otherwise (collectively, “transfer”) any Shares acquired upon exercise of this
option, then the Participant shall first give written notice of the proposed transfer (the “Transfer Notice”) to the Company. The Transfer Notice shall name the proposed transferee and state the number of such Shares the Participant
proposes to transfer (the “Offered Shares”), the price per share and all other material terms and conditions of the transfer. 

  
 - 2 - 

 (b) Company Right to Purchase. For 30 days following its receipt of such Transfer
Notice, the Company shall have the option to purchase all or part of the Offered Shares at the price and upon the terms set forth in the Transfer Notice. In the event the Company elects to purchase all or part of the Offered Shares, it shall give
written notice of such election to the Participant within such 30-day period. Within 10 days after his or her receipt of such notice, the Participant shall tender to the Company at its principal offices the
certificate or certificates representing the Offered Shares to be purchased by the Company, duly endorsed in blank by the Participant or with duly endorsed stock powers attached thereto, all in a form suitable for transfer of the Offered Shares to
the Company. Promptly following receipt of such certificate or certificates, the Company shall deliver or mail to the Participant a check in payment of the purchase price for such Offered Shares; provided that if the terms of payment
set forth in the Transfer Notice were other than cash against delivery, the Company may pay for the Offered Shares on the same terms and conditions as were set forth in the Transfer Notice; and provided further that any delay in making
such payment shall not invalidate the Company’s exercise of its option to purchase the Offered Shares. 
 (c) Shares Not Purchased
By Company. If the Company does not elect to acquire all of the Offered Shares, the Participant may, within the 30-day period following the expiration of the option granted to the Company under subsection
(b) above, transfer the Offered Shares which the Company has not elected to acquire to the proposed transferee, provided that such transfer shall not be on terms and conditions more favorable to the transferee than those contained
in the Transfer Notice. Notwithstanding any of the above, all Offered Shares transferred pursuant to this Section 4 shall remain subject to the right of first refusal set forth in this Section 4 and such 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 Section 4. 

(d) Consequences of Non-Delivery. After the time at which the Offered Shares are required to be
delivered to the Company for transfer to the Company pursuant to subsection (b) above, the Company shall not pay any dividend to the Participant on account of such Offered Shares or permit the Participant to exercise any of the privileges or
rights of a stockholder with respect to such Offered Shares, but shall, insofar as permitted by law, treat the Company as the owner of such Offered Shares. 

(e) Exempt Transactions. The following transactions shall be exempt from the provisions of this Section 4: 

(1) any transfer of Shares to or for the benefit of any spouse, child or grandchild of the Participant, or to a trust for their benefit; 

(2) any transfer pursuant to an effective registration statement filed by the Company under the Securities Act of 1933, as amended (the
“Securities Act”); and 

  
 - 3 - 

 (3) the sale of all or substantially all of the outstanding shares of capital stock of the
Company (including pursuant to a merger or consolidation); 
 provided, however, that in the case of a transfer pursuant to clause
(1) above, such Shares shall remain subject to the right of first refusal set forth in this Section 4 and such 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 Section 4. 
 (f) Assignment of Company Right. The Company may assign
its rights to purchase Offered Shares in any particular transaction under this Section 4 to one or more persons or entities. 
 (g)
Termination. The provisions of this Section 4 shall terminate upon the earlier of the following events: 
 (1) the closing of the
sale of shares of Common Stock in an underwritten public offering pursuant to an effective registration statement filed by the Company under the Securities Act; or 

(2) the sale of all or substantially all of the outstanding shares of capital stock, assets or business of the Company, by merger,
consolidation, sale of assets or otherwise (other than a merger or consolidation in which all or substantially all of the individuals and entities who were beneficial owners of the Company’s voting securities immediately prior to such
transaction beneficially own, directly or indirectly, more than 75% (determined on an as-converted basis) of the outstanding securities entitled to vote generally in the election of directors of the resulting,
surviving or acquiring corporation in such transaction). 
 (h) No Obligation to Recognize Invalid Transfer. The Company shall not be
required (1) to transfer on its books any of the Shares which shall have been sold or transferred in violation of any of the provisions set forth in this Section 4, or (2) to treat as owner of such Shares or to pay dividends to any
transferee to whom any such Shares shall have been so sold or transferred. 
 (i) Legends. The certificate representing Shares shall
bear a legend substantially in the following form (in addition to, or in combination with, any legend required by applicable federal and state securities laws and agreements relating to the transfer of the Company securities): 

“The shares represented by this certificate are subject to a right of first refusal in favor of the Company, as provided in a certain
stock option agreement with the Company.” 
 5. Agreement in Connection with Initial Public Offering. 

The Participant agrees, in connection with the initial underwritten public offering of the Common Stock pursuant to a registration statement under the
Securities Act, (0 not to (a) offer, pledge, announce the intention to sell, 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, or otherwise
transfer or dispose of, directly or indirectly, any shares of Common Stock or any other securities of the Company or (b) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership
of shares of Common Stock or other securities of the 

  
 - 4 - 

 
Company, whether any transaction described in clause (a) or (b) is to be settled by delivery of securities, in cash or otherwise, during the period beginning on the date of the filing of
such registration statement with the Securities and Exchange Commission and ending 180 days after the date of the final prospectus relating to the offering (plus up to an additional 34 days to the extent requested by the managing underwriters for
such offering in order to address Rule 2711(f) of the National Association of Securities Dealers, Inc. or any similar successor provision), and (ii) to execute any agreement reflecting clause (i) above as may be requested by the Company or
the managing underwriters at the time of such offering. 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 the “lock-up” period. 
 6. Other Matters. 

(a) Withholding. No Shares will be issued pursuant to the exercise of this option unless and until the Company satisfies all applicable
federal, state, and local or other income and employment tax withholding obligations as described in the Plan. 
 (b) Disqualifying
Disposition. If the Participant disposes of Shares acquired upon exercise of this option within two years from the Grant date (as set forth in the Carta Notice) or one year after such Shares were acquired pursuant to exercise of this option, the
Participant shall notify the Company in writing of such disposition. 
 (c) Electronic Delivery of Documents. The Participant agrees
to accept by email all documents relating to the Company, the Plan or this option and all other documents that the Company is required to deliver to its security holders (including, without limitation, disclosures that may be required by the
Securities and Exchange Commission). The Participant also agrees that the Company may deliver these documents by posting them on a website maintained by the Company or by a third party under contract with the Company. If the Company posts these
documents on a website, it shall notify the Participant by email of their availability. The Participant acknowledges that he or she may incur costs in connection with electronic delivery, including the cost of accessing the internet and printing
fees, and that an interruption of Internet access may interfere with his or her ability to access the documents. This consent shall remain in effect until this option expires or until the Participant gives the Company written notice that it should
deliver paper documents. 
 7. Transfer Restrictions. 

(a) This option may not be sold, assigned, transferred, pledged or otherwise encumbered by the Participant, either voluntarily or by operation
of law, except by will or the laws of descent and distribution, and, during the lifetime of the Participant, this option shall be exercisable only by the Participant. 

(b) The Participant agrees that he or she will not transfer any Shares issued pursuant to the exercise of this option unless the transferee,
as a condition to such transfer, delivers to the Company a written instrument confirming that such transferee shall be bound by all of the terms and conditions of Section 4 and Section 5; provided that such a written confirmation shall not
be required with respect to (1) Section 4 after such provision has terminated in accordance with Section 4(g) or (2) Section 5 after the completion of the lock-up period in connection
with the Company’s initial underwritten public offering. 

  
 - 5 - 

 8. Provisions of the Plan. 

This option is subject to the provisions of the Plan (including the provisions relating to amendments to the Plan), a copy of which is
furnished to the Participant with this option. 
 IN WITNESS WHEREOF, the Company has caused this option to be executed under its corporate
seal by its duly authorized officer. This option shall take effect as a sealed instrument. 
  

			
	KEROS THERAPEUTICS, INC.
		
	By:	 	 
		
		 	Name:                                     
                                         
        
		
		 	Title:                                    
                                         
           

  
 - 6 - 

 PARTICIPANTS ACCEPTANCE 

The undersigned hereby accepts the foregoing option and agrees to the terms and conditions thereof The undersigned hereby acknowledges receipt
of a copy of the Company’s 2017 Stock Incentive Plan. 
  

			
	PARTICIPANT:
	
	 
	
	Address:
	
	 
	
	 

 Exhibit A 

NOTICE OF STOCK OPTION EXERCISE 

Date: ____________1 

Keros Therapeutics, Inc. 
 [INSERT ADDRESS] 

Attention: Treasurer 
 Dear Sir or Madam: 

I am the holder of ____________2 Stock Option granted to me under the Keros Therapeutics,
Inc. (the “Company”) 2017 Stock Incentive Plan on ____________3 for the purchase of ____________4 shares of Common Stock of the
Company at a purchase price of $_________5 per share. 
 I hereby exercise my option to
purchase ____________6 shares of Common Stock (the “Shares”), for which I have enclosed ____________7 in the amount of ____________8. Please register my stock certificate as follows: 

Name(s):                      
                                         
          9 

Address:                    
                                         
              
 Tax I.D.
#:                                        
                               10

  

	1 	 Enter the date of exercise. 

	2 	 Enter either “an Incentive” or “a Nonstatutory”. 

	3 	 Enter the date of grant. 

	4 	 Enter the total number of shares of Common Stock for which the option was granted. 

	5 	 Enter the option exercise price per share of Common Stock. 

	6 	 Enter the number of shares of Common Stock to be purchased upon exercise of all or part of the option.

	7 	 Enter “cash”, “personal check” or if permitted by the option or Plan, “stock
certificates No. XXXX and =DC”. 

	8 	 Enter the dollar amount (price per share of Common Stock times the number of shares of Common Stock to be
purchased), or the number of shares tendered. Fair market value of shares tendered, together with cash or check, must cover the purchase price of the shares issued upon exercise. 

	9 	 Enter name(s) to appear on stock certificate: (a) Your name only; (b) Your name and other name (i.e.,
John Doe and Jane Doe, Joint Tenants With Right of Survivorship); or (c) In the case of a Nonstatutory option only, a Child’s name, with you as custodian (i.e., Jane Doe, Custodian for Tommy Doe). Note: There may be income and/or gift tax
consequences of registering shares in a Child’s name. 

	10 	 Social Security Number of Holder(s). 

 I represent, warrant and covenant as follows: 

1. I am purchasing the Shares for my own account for investment only, and not with a view to, or for sale in connection with, any distribution of the Shares in
violation of the Securities Act of 1933 (the “Securities Act”), or any rule or regulation under the Securities Act. 
 2. I have had such
opportunity as I have deemed adequate to obtain from representatives of the Company such information as is necessary to permit me to evaluate the merits and risks of my investment in the Company. 

3. I have sufficient experience in business, financial and investment matters to be able to evaluate the risks involved in the purchase of the Shares and to
make an informed investment decision with respect to such purchase. 
 4. I can afford a complete loss of the value of the Shares and am able to bear the
economic risk of holding such Shares for an indefinite period. 
 5. I understand that (i) the Shares have not been registered under the Securities Act
and are “restricted securities” within the meaning of Rule 144 under the Securities Act, (ii) the Shares cannot be sold, transferred or otherwise disposed of unless they are subsequently registered under the Securities Act or an
exemption from registration is then available; (iii) in any event, the exemption from registration under Rule 144 will not be available for at least one year and even then will not be available unless a public market then exists for the Common
Stock, adequate information concerning the Company is then available to the public, and other terms and conditions of Rule 144 are complied with; and (iv) there is now no registration statement on file with the Securities and Exchange
Commission with respect to any stock of the Company and the Company has no obligation or current intention to register the Shares under the Securities Act. 

Very truly yours, 

	
	
	   

	(Signature)

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