Document:

EX-10.5

 Exhibit 10.5 

KEROS THERAPEUTICS, INC. 

STOCK OPTION GRANT NOTICE 

(2020 EQUITY INCENTIVE PLAN) 

Keros Therapeutics, Inc. (the “Company”), pursuant to its 2020 Equity Incentive Plan (the “Plan”), has granted
to you (“Optionholder”) an option to purchase the number of shares of the Common Stock set forth below (the “Option”). Your Option is subject to all of the terms and conditions as set forth herein and
in the Plan, and the Stock Option Agreement and the Notice of Exercise, all of which are attached hereto and incorporated herein in their entirety. Capitalized terms not explicitly defined herein but defined in the Plan or the Stock Option Agreement
shall have the meanings set forth in the Plan or the Stock Option Agreement, as applicable. 
  

			
	 Optionholder:
	 	
                   
                     

	 Date of Grant:
	 	
                   
                     

	 Vesting Commencement Date:
	 	
                   
                     

	 Number of Shares of Common Stock Subject to Option:
	 	
                   
                     

	 Exercise Price (Per Share):
	 	
                   
                     

	 Total Exercise Price:
	 	
                   
                     

	 Expiration Date:
	 	
                   
                     

  

			
	Type of Grant:	  	[Incentive Stock Option] OR [Nonstatutory Stock Option]
		
	Exercise and Vesting Schedule:	  	Subject to the Optionholder’s Continuous Service through each applicable vesting date, the Option will vest as follows:
		
		  	[1/4th of the shares vest and become exercisable one year after the Vesting Commencement Date; the balance of the shares vest and become exercisable in a series of thirty-six (36) successive equal monthly installments measured from the first anniversary of the Vesting Commencement Date on the same date of the month as the Vesting Commencement Date. [Notwithstanding the
foregoing, the Option will accelerate vesting and exercisability in full upon a Change in Control which occurs during your Continuous Service.]]

 Optionholder Acknowledgements: By your signature below or by electronic acceptance or authentication in a form
authorized by the Company, you understand and agree that: 
  

	 	•	 	 The Option is governed by this Stock Option Grant Notice, and the provisions of the Plan and the Stock Option
Agreement and the Notice of Exercise, all of which are made a part of this document. Unless otherwise provided in the Plan, this Grant Notice and the Stock Option Agreement (together, the “Option Agreement”) may not be
modified, amended or revised except in a writing signed by you and a duly authorized officer of the Company. 

  

	 	•	 	 [If the Option is an Incentive Stock Option, it (plus other outstanding Incentive Stock Options granted to you)
cannot be first exercisable for more than $100,000 in value (measured by exercise price) in any calendar year. Any excess over $100,000 is a Nonstatutory Stock Option.] 

 

	 	•	 	 You consent to receive this Grant Notice, the Stock Option Agreement, the Plan, the Prospectus and any other
Plan-related documents by electronic delivery and to participate in the Plan through an on-line or electronic system established and maintained by the Company or another third party designated by the Company.

	 	•	 	 You have read and are familiar with the provisions of the Plan, the Stock Option Agreement, the Notice of
Exercise and the Prospectus. In the event of any conflict between the provisions in this Grant Notice, the Option Agreement, the Notice of Exercise, or the Prospectus and the terms of the Plan, the terms of the Plan shall control.

  

	 	•	 	 The Option Agreement sets forth the entire understanding between you and the Company regarding the acquisition of
Common Stock and supersedes all prior oral and written agreements, promises and/or representations on that subject with the exception of other equity awards previously granted to you and any written employment agreement, offer letter, severance
agreement, written severance plan or policy, or other written agreement between the Company and you in each case that specifies the terms that should govern this Option. 

 

	 	•	 	 Counterparts may be delivered via facsimile, electronic mail (including pdf or any electronic signature complying
with the U.S. federal ESIGN Act of 2000, Uniform Electronic Transactions Act or other applicable law) or other transmission method and any counterpart so delivered will be deemed to have been duly and validly delivered and be valid and effective for
all purposes. 

  

									
	KEROS THERAPEUTICS, INC.	 		 	OPTIONHOLDER:
				
	By:	 	
                     
                                         
                  
	 		 	
                     
                                        

	Signature	 		 		 	Signature
	Title:	 	
                     
                                        
	 		 	Date:	 	     
                                         
   

	Date:	 	  
	 		 		 	

 ATTACHMENTS: Stock Option Agreement, 2020 Equity Incentive Plan, Notice of Exercise 

 KEROS THERAPEUTICS, INC. 

2020 EQUITY INCENTIVE PLAN 

STOCK OPTION AGREEMENT 

As reflected by your Stock Option Grant Notice (“Grant Notice”), Keros Therapeutics, Inc. (the
“Company”) has granted you an option under its 2020 Equity Incentive Plan (the “Plan”) to purchase a number of shares of Common Stock at the exercise price indicated in your Grant Notice (the
“Option”). Capitalized terms not explicitly defined in this Agreement but defined in the Grant Notice or the Plan shall have the meanings set forth in the Grant Notice or Plan, as applicable. The terms of your Option as
specified in the Grant Notice and this Stock Option Agreement constitute your Option Agreement. 
 The general terms and conditions
applicable to your Option are as follows: 
 1.    GOVERNING PLAN
DOCUMENT. Your Option is subject to all the provisions of the Plan, including but not limited to the provisions in: 

(a)    Section 6 regarding the impact of a Capitalization Adjustment, dissolution, liquidation, or Corporate
Transaction on your Option; 
 (b)    Section 9(e) regarding the Company’s retained rights to terminate
your Continuous Service notwithstanding the grant of the Option; and 
 (c)    Section 8(c) regarding the tax
consequences of your Option. 
 Your Option is further subject to all interpretations, amendments, rules and regulations, which may from time to time be
promulgated and adopted pursuant to the Plan. In the event of any conflict between the Option Agreement and the provisions of the Plan, the provisions of the Plan shall control. 

2.    EXERCISE. 

(a)    You may generally exercise the vested portion of your Option for whole shares of Common Stock at any time
during its term by delivery of payment of the exercise price and applicable withholding taxes and other required documentation to the Plan Administrator in accordance with the exercise procedures established by the Plan Administrator, which may
include an electronic submission. Please review Sections 4(i), 4(j) and 7(b)(v) of the Plan, which may restrict or prohibit your ability to exercise your Option during certain periods. 

(b)    To the extent permitted by Applicable Law, you may pay your Option exercise price as follows: 

(i)    cash, check, bank draft or money order; 

 (ii)    subject to Company and/or Committee consent at the time
of exercise, pursuant to a “cashless exercise” program as further described in Section 4(c)(ii) of the Plan if at the time of exercise the Common Stock is publicly traded; 

(iii)    subject to Company and/or Committee consent at the time of exercise, by delivery of previously owned
shares of Common Stock as further described in Section 4(c)(iii) of the Plan; or 
 (iv)    subject to
Company and/or Committee consent at the time of exercise, if the Option is a Nonstatutory Stock Option, by a “net exercise” arrangement as further described in Section 4(c)(iv) of the Plan. 

(c)    By accepting your Option, you agree that you will not sell, dispose of, transfer, make any short sale of,
grant any option for the purchase of, or enter into any hedging or similar transaction with the same economic effect as a sale with respect to any shares of Common Stock or other securities of the Company held by you, for a period of one hundred
eighty (180) days following the effective date of a registration statement of the Company filed under the Securities Act or such longer period as the underwriters or the Company will request to facilitate compliance with FINRA Rule 2241 or any
successor or similar rules or regulation (the “Lock-Up Period”); provided, however, that nothing contained in this section will prevent the exercise of a repurchase option, if
any, in favor of the Company during the Lock-Up Period. You further agree to execute and deliver such other agreements as may be reasonably requested by the Company or the underwriters that are consistent with
the foregoing or that are necessary to give further effect thereto. In order to enforce the foregoing covenant, the Company may impose stop-transfer instructions with respect to your shares of Common Stock until the end of such period. You also
agree that any transferee of any shares of Common Stock (or other securities) of the Company held by you will be bound by this Section 2(c). The underwriters of the Company’s stock are intended third party beneficiaries of this
Section 2(c) and will have the right, power and authority to enforce the provisions hereof as though they were a party hereto. 

3.    TERM. You may not exercise your Option before the commencement of its term or after its
term expires. The term of your Option commences on the Date of Grant and expires upon the earliest of the following: 

(a)    immediately upon the termination of your Continuous Service for Cause; 

(b)    three months after the termination of your Continuous Service for any reason other than Cause, Disability
or death; 
 (c)    12 months after the termination of your Continuous Service due to your Disability; 

(d)    24 months after your death if you die during your Continuous Service; 

(e)    immediately upon a Corporate Transaction if the Board has determined that the Option will terminate in
connection with a Corporate Transaction, 
 (f)    the Expiration Date indicated in your Grant Notice; or 

 (g)    the day before the 10th anniversary of the Date of Grant.

 Notwithstanding the foregoing, if you die during the period provided in Section 3(b) or 3(c) above, the term of your Option shall
not expire until the earlier of (i) 24 months after your death, (ii) upon any termination of the Option in connection with a Corporate Transaction, (iii) the Expiration Date indicated in your Grant Notice, or (iv) the day before the
tenth anniversary of the Date of Grant. Additionally, the Post-Termination Exercise Period of your Option may be extended as provided in Section 4(i) of the Plan. 

To obtain the federal income tax advantages associated with an Incentive Stock Option, the Code requires that at all times beginning on the
date of grant of your Option and ending on the day three months before the date of your Option’s exercise, you must be an employee of the Company or an Affiliate, except in the event of your death or Disability. If the Company provides for the
extended exercisability of your Option under certain circumstances for your benefit, your Option will not necessarily be treated as an Incentive Stock Option if you exercise your Option more than three months after the date your employment
terminates. 
 4.    WITHHOLDING OBLIGATIONS. As further provided in
Section 8 of the Plan: (a) you may not exercise your Option unless the applicable tax withholding obligations are satisfied, and (b) at the time you exercise your Option, in whole or in part, or at any time thereafter as requested by
the Company, you hereby authorize withholding from payroll and any other amounts payable to you, and otherwise agree to make adequate provision for (including by means of a “cashless exercise” pursuant to a program developed under
Regulation T as promulgated by the Federal Reserve Board to the extent permitted by the Company), any sums required to satisfy the federal, state, local and foreign tax withholding obligations, if any, which arise in connection with the exercise of
your Option in accordance with the withholding procedures established by the Company. Accordingly, you may not be able to exercise your Option even though the Option is vested, and the Company shall have no obligation to issue shares of Common Stock
subject to your Option, unless and until such obligations are satisfied. In the event that the amount of the Company’s withholding obligation in connection with your Option was greater than the amount actually withheld by the Company, you agree
to indemnify and hold the Company harmless from any failure by the Company to withhold the proper amount. 

5.    INCENTIVE STOCK OPTION DISPOSITION
REQUIREMENT. If your Option is an Incentive Stock Option, you must notify the Company in writing within 15 days after the date of any disposition of any of the shares of the Common Stock issued upon exercise of your Option that
occurs within two years after the date of your Option grant or within one year after such shares of Common Stock are transferred upon exercise of your Option. 

6.    TRANSFERABILITY. Except as otherwise provided in Section 4(e) of the Plan, your
Option is not transferable, except by will or by the applicable laws of descent and distribution, and is exercisable during your life only by you. 

7.    CORPORATE TRANSACTION. Your Option is subject to the terms of any
agreement governing a Corporate Transaction involving the Company, including, without limitation, a provision for the appointment of a stockholder representative that is authorized to act on your behalf with respect to any escrow, indemnities and
any contingent consideration. 

 8.    NO LIABILITY
FOR TAXES. As a condition to accepting the Option, you hereby (a) agree to not make any claim against the Company, or any of its Officers, Directors, Employees or Affiliates related
to tax liabilities arising from the Option or other Company compensation and (b) acknowledge that you were advised to consult with your own personal tax, financial and other legal advisors regarding the tax consequences of the Option and have
either done so or knowingly and voluntarily declined to do so. Additionally, you acknowledge that the Option is exempt from Section 409A only if the exercise price is at least equal to the “fair market value” of the Common Stock on
the date of grant as determined by the Internal Revenue Service and there is no other impermissible deferral of compensation associated with the Option. Additionally, as a condition to accepting the Option, you agree not make any claim against the
Company, or any of its Officers, Directors, Employees or Affiliates in the event that the Internal Revenue Service asserts that such exercise is less than the “fair market value” of the Common Stock on the date of grant as subsequently
determined by the Internal Revenue Service. 

9.    SEVERABILITY. If any part of this Option Agreement or the
Plan is declared by any court or governmental authority to be unlawful or invalid, such unlawfulness or invalidity will not invalidate any portion of this Option Agreement or the Plan not declared to be unlawful or invalid. Any Section of this
Option Agreement (or part of such a Section) so declared to be unlawful or invalid will, if possible, be construed in a manner which will give effect to the terms of such Section or part of a Section to the fullest extent possible while remaining
lawful and valid 
 10.    OTHER DOCUMENTS. You hereby acknowledge
receipt of or the right to receive a document providing the information required by Rule 428(b)(1) promulgated under the Securities Act, which includes the Prospectus. In addition, you acknowledge receipt of the Company’s Trading Policy.

 11.    QUESTIONS. If you have questions regarding these or any other terms and
conditions applicable to your Option, including a summary of the applicable federal income tax consequences please see the Prospectus. 
 * *
* * 

 KEROS THERAPEUTICS, INC. 

(2020 EQUITY INCENTIVE PLAN) 

NOTICE OF EXERCISE 
 KEROS
THERAPEUTICS, INC. 
 99 HAYDEN AVENUE, SUITE 120, BUILDING
E 
 LEXINGTON, MASSACHUSETTS
02421                                        
                                         
                   Date of Exercise:
                     
 This
constitutes notice to KEROS THERAPEUTICS, INC. (the “Company”) that I elect to purchase the below number of shares of Common Stock of the Company
(the “Shares”) by exercising my Option for the price set forth below. Capitalized terms not explicitly defined in this Notice of Exercise but defined in the Grant Notice, Option Agreement or 2020 EQUITY
INCENTIVE PLAN (the “Plan”) shall have the meanings set forth in the Grant Notice, Option Agreement or Plan, as applicable. Use of certain payment methods is subject to Company
and/or Committee consent and certain additional requirements set forth in the Option Agreement and the Plan. 
  

									
			
	 Type of option (check one):
	  	 	Incentive 	☐ 	 	 	Nonstatutory 	☐ 
			
	 Date of Grant:
	  	 	            	 	 			
			
	 Number of Shares as to which Option is exercised:
	  	 	            	 	 			
			
	 Certificates to be issued in name of:
	  	 	            	 	 			
			
	 Total exercise price:
	  	$	             	 	 			
			
	 Cash, check, bank draft or money order delivered herewith:
	  	$	             	 	 			
			
	 Value of                  Shares
delivered herewith:
	  	$	             	 	 			
			
	 Regulation T Program (cashless exercise)
	  	$	             	 	 			
			
	 Value of                  Shares
pursuant to net exercise:
	  	$	             	 	 			

 By this exercise, I agree (i) to provide such additional documents as you may require
pursuant to the terms of the Plan, (ii) to satisfy the tax withholding obligations, if any, relating to the exercise of this Option as set forth in the Option Agreement, and (iii) if this exercise relates to an incentive stock option, to
notify you in writing within 15 days after the date of any disposition of any of the Shares issued upon exercise of this Option that occurs within two years after the Date of Grant or within one year after such Shares are issued upon exercise of
this Option. 
 I further agree that, if required by the Company (or a representative of the underwriters) in connection with the first
underwritten registration of the offering of any securities of the Company under the Securities Act, I will not sell, dispose of, transfer, make any short sale of, grant any option for the purchase of, or enter into any hedging or similar
transaction with the same economic effect as a sale with respect to any shares of Common Stock or other securities of the Company for a period of one hundred eighty (180) days following the effective date of a registration statement of the
Company filed under the Securities Act (or such longer period as the underwriters or the Company shall request to facilitate compliance with FINRA Rule 2241 or any successor or similar rule or regulation) (the “Lock-Up Period”). I further agree to execute and deliver such other agreements as may be reasonably requested by the Company or the underwriters that are consistent with the foregoing or that are
necessary to give further effect thereto. In order to enforce the foregoing covenant, the Company may impose stop-transfer instructions with respect to securities subject to the foregoing restrictions until
the end of such period. 
  

	
	Very truly yours,EX-10.6

 Exhibit 10.6 

KEROS THERAPEUTICS, INC. 

2020 EMPLOYEE STOCK PURCHASE PLAN 

ADOPTED BY THE BOARD OF DIRECTORS:
[            ], 2020 
 APPROVED BY
THE STOCKHOLDERS: [            ], 2020 

1.    GENERAL; PURPOSE. 

(a)    The Plan provides a means by which Eligible Employees of the Company and certain designated Related
Corporations may be given an opportunity to purchase shares of Common Stock. The Plan permits the Company to grant a series of Purchase Rights to Eligible Employees under an Employee Stock Purchase Plan. 

(b)    The Company, by means of the Plan, seeks to retain the services of such Employees, to secure and retain the
services of new Employees and to provide incentives for such persons to exert maximum efforts for the success of the Company and its Related Corporations. 

2.    ADMINISTRATION. 

(a)    The Board will administer the Plan unless and until the Board delegates administration of the Plan to a
Committee or Committees, as provided in Section 2(c). 
 (b)    The Board will have the power, subject to,
and within the limitations of, the express provisions of the Plan: 
 (i)    To determine how and when Purchase
Rights will be granted and the provisions of each Offering (which need not be identical). 
 (ii)    To designate
from time to time which Related Corporations of the Company will be eligible to participate in the Plan. 

(iii)    To construe and interpret the Plan and Purchase Rights, and to establish, amend and revoke rules and
regulations for its administration. The Board, in the exercise of this power, may correct any defect, omission or inconsistency in the Plan, in a manner and to the extent it deems necessary or expedient to make the Plan fully effective. 

(iv)    To settle all controversies regarding the Plan and Purchase Rights granted under the Plan. 

(v)    To suspend or terminate the Plan at any time as provided in Section 12. 

(vi)    To amend the Plan at any time as provided in Section 12. 

(vii)    Generally, to exercise such powers and to perform such acts as it deems necessary or expedient to promote
the best interests of the Company and its Related Corporations and to carry out the intent that the Plan be treated as an Employee Stock Purchase Plan. 

(viii)    To adopt such procedures and sub-plans as are necessary or
appropriate to permit participation in the Plan by Employees who are foreign nationals or employed outside the United States. 

  
 1 

 (c)    The Board may delegate some or all of the administration
of the Plan to a Committee or Committees. If administration is delegated to a Committee, the Committee will have, in connection with the administration of the Plan, the powers theretofore possessed by the Board that have been delegated to the
Committee, including the power to delegate to a subcommittee any of the administrative powers the Committee is authorized to exercise (and references to the Board in this Plan and in any applicable Offering Document will thereafter be to the
Committee or subcommittee), subject, however, to such resolutions, not inconsistent with the provisions of the Plan, as may be adopted from time to time by the Board. The Board may retain the authority to concurrently administer the Plan with the
Committee and may, at any time, revest in the Board some or all of the powers previously delegated. Whether or not the Board has delegated administration of the Plan to a Committee, the Board will have the final power to determine all questions of
policy and expediency that may arise in the administration of the Plan. 
 (d)    All determinations,
interpretations and constructions made by the Board in good faith will not be subject to review by any person and will be final, binding and conclusive on all persons. 

3.    SHARES OF COMMON STOCK SUBJECT TO
THE PLAN. 
 (a)    Subject to the provisions of Section 11(a) relating to
Capitalization Adjustments, the maximum number of shares of Common Stock that may be issued under the Plan will not exceed [        ] shares of Common Stock, plus the number of shares of Common Stock that are
automatically added on January 1st of each year for a period of up to ten years, commencing on the first January 1 following the IPO Date and ending on (and including) January 1, 2030, in an amount equal to the lesser of (i)
[    ] % of the total number of shares of Capital Stock outstanding on December 31st of the preceding calendar year, and (ii) [        ] shares of Common Stock. Notwithstanding the
foregoing, the Board may act prior to the first day of any calendar year to provide that there will be no January 1st increase in the share reserve for such calendar year or that the increase in
the share reserve for such calendar year will be a lesser number of shares of Common Stock than would otherwise occur pursuant to the preceding sentence. 

(b)    If any Purchase Right granted under the Plan terminates without having been exercised in full, the shares of
Common Stock not purchased under such Purchase Right will again become available for issuance under the Plan. 

(c)    The stock purchasable under the Plan will be shares of authorized but unissued or reacquired Common Stock,
including shares repurchased by the Company on the open market. 
 4.    GRANT OF
PURCHASE RIGHTS; OFFERING. 
 (a)    The Board may from time to
time grant or provide for the grant of Purchase Rights to Eligible Employees under an Offering (consisting of one or more Purchase Periods) on an Offering Date or Offering Dates selected by the Board. Each Offering will be in such form and will
contain such terms and conditions as the Board will deem appropriate, and will comply with the requirement of Section 423(b)(5) of the Code that all Employees granted Purchase Rights will have the same rights and privileges. The terms and
conditions of an Offering shall be incorporated by reference into the Plan and treated as part of the Plan. The provisions of separate Offerings need not be identical, but each Offering will include (through incorporation of the provisions of this
Plan by reference in the document comprising the Offering or otherwise) the period during which the Offering will be effective, which period will not exceed 27 months beginning with the Offering Date, and the substance of the provisions contained in
Sections 5 through 8, inclusive. 

  
 2 

 (b)    If a Participant has more than one Purchase Right
outstanding under the Plan, unless he or she otherwise indicates in forms delivered to the Company: (i) each form will apply to all of his or her Purchase Rights under the Plan, and (ii) a Purchase Right with a lower exercise price (or an
earlier-granted Purchase Right, if different Purchase Rights have identical exercise prices) will be exercised to the fullest possible extent before a Purchase Right with a higher exercise price (or a later-granted Purchase Right if different
Purchase Rights have identical exercise prices) will be exercised. 
 (c)    The Board will have the discretion
to structure an Offering so that if the Fair Market Value of a share of Common Stock on the first Trading Day of a new Purchase Period within that Offering is less than or equal to the Fair Market Value of a share of Common Stock on the Offering
Date for that Offering, then (i) that Offering will terminate immediately as of that first Trading Day, and (ii) the Participants in such terminated Offering will be automatically enrolled in a new Offering beginning on the first Trading
Day of such new Purchase Period. 
 5.    ELIGIBILITY. 

(a)    Purchase Rights may be granted only to Employees of the Company or, as the Board may designate in accordance
with Section 2(b), to Employees of a Related Corporation. Except as provided in Section 5(b), an Employee will not be eligible to be granted Purchase Rights unless, on the Offering Date, the Employee has been in the employ of the Company
or the Related Corporation, as the case may be, for such continuous period preceding such Offering Date as the Board may require, but in no event will the required period of continuous employment be equal to or greater than two years. In addition,
the Board may provide that no Employee will be eligible to be granted Purchase Rights under the Plan unless, on the Offering Date, such Employee’s customary employment with the Company or the Related Corporation is more than 20 hours per week
and more than five months per calendar year or such other criteria as the Board may determine consistent with Section 423 of the Code. 

(b)    The Board may provide that each person who, during the course of an Offering, first becomes an Eligible
Employee will, on a date or dates specified in the Offering which coincides with the day on which such person becomes an Eligible Employee or which occurs thereafter, receive a Purchase Right under that Offering, which Purchase Right will thereafter
be deemed to be a part of that Offering. Such Purchase Right will have the same characteristics as any Purchase Rights originally granted under that Offering, as described herein, except that: 

(i)    the date on which such Purchase Right is granted will be the “Offering Date” of such Purchase
Right for all purposes, including determination of the exercise price of such Purchase Right; 
 (ii)    the
period of the Offering with respect to such Purchase Right will begin on its Offering Date and end coincident with the end of such Offering; and 

(iii)    the Board may provide that if such person first becomes an Eligible Employee within a specified period of
time before the end of the Offering, he or she will not receive any Purchase Right under that Offering. 

(c)    No Employee will be eligible for the grant of any Purchase Rights if, immediately after any such Purchase
Rights are granted, such Employee owns stock possessing five percent or more of the total combined voting power or value of all classes of stock of the Company or of any Related Corporation. For purposes of this Section 5(c), the rules of
Section 424(d) of the Code will apply in determining the stock ownership of any Employee, and stock which such Employee may purchase under all outstanding Purchase Rights and options will be treated as stock owned by such Employee. 

  
 3 

 (d)    As specified by Section 423(b)(8) of the Code, an
Eligible Employee may be granted Purchase Rights only if such Purchase Rights, together with any other rights granted under all Employee Stock Purchase Plans of the Company and any Related Corporations, do not permit such Eligible Employee’s
rights to purchase stock of the Company or any Related Corporation to accrue at a rate which, when aggregated, exceeds $25,000 of Fair Market Value of such stock (determined at the time such rights are granted, and which, with respect to the Plan,
will be determined as of their respective Offering Dates) for each calendar year in which such rights are outstanding at any time. 

(e)    Officers of the Company and any designated Related Corporation, if they are otherwise Eligible Employees,
will be eligible to participate in Offerings under the Plan. Notwithstanding the foregoing, the Board may provide in an Offering that Employees who are highly compensated Employees within the meaning of Section 423(b)(4)(D) of the Code will not
be eligible to participate. 
 6.    PURCHASE RIGHTS; PURCHASE PRICE.

 (a)    On each Offering Date, each Eligible Employee, pursuant to an Offering made under the Plan, will be
granted a Purchase Right to purchase up to that number of shares of Common Stock purchasable either with a percentage or with a maximum dollar amount, as designated by the Board, but in either case not exceeding [15]% of such Employee’s
earnings (as defined by the Board in each Offering) during the period that begins on the Offering Date (or such later date as the Board determines for a particular Offering) and ends on the date stated in the Offering, which date will be no later
than the end of the Offering. 
 (b)    The Board will establish one or more Purchase Dates during an Offering on
which Purchase Rights granted for that Offering will be exercised and shares of Common Stock will be purchased in accordance with such Offering. 

(c)    In connection with each Offering made under the Plan, the Board may specify (i) a maximum number of
shares of Common Stock that may be purchased by any Participant on any Purchase Date during such Offering, (ii) a maximum aggregate number of shares of Common Stock that may be purchased by all Participants pursuant to such Offering and/or
(iii) a maximum aggregate number of shares of Common Stock that may be purchased by all Participants on any Purchase Date under the Offering. If the aggregate purchase of shares of Common Stock issuable upon exercise of Purchase Rights granted
under the Offering would exceed any such maximum aggregate number, then, in the absence of any Board action otherwise, a pro rata (based on each Participant’s accumulated Contributions) allocation of the shares of Common Stock available will be
made in as nearly a uniform manner as will be practicable and equitable. 
 (d)    The purchase price of shares
of Common Stock acquired pursuant to Purchase Rights will be not less than the lesser of: 
 (i)    an amount
equal to 85% of the Fair Market Value of the shares of Common Stock on the Offering Date; or 
 (ii)    an amount
equal to 85% of the Fair Market Value of the shares of Common Stock on the applicable Purchase Date. 

7.    PARTICIPATION; WITHDRAWAL; TERMINATION. 

(a)    An Eligible Employee may elect to participate in an Offering and authorize payroll deductions as the means of
making Contributions by completing and delivering to the Company, within 

  
 4 

 
the time specified in the Offering, an enrollment form provided by the Company. The enrollment form will specify the amount of Contributions not to exceed the maximum amount specified by the
Board. Each Participant’s Contributions will be credited to a bookkeeping account for such Participant under the Plan and will be deposited with the general funds of the Company except where applicable law requires that Contributions be
deposited with a third party. If permitted in the Offering, a Participant may begin such Contributions with the first practicable payroll occurring on or after the Offering Date (or, in the case of a payroll date that occurs after the end of the
prior Offering but before the Offering Date of the next new Offering, Contributions from such payroll will be included in the new Offering). If permitted in the Offering, a Participant may thereafter reduce (including to zero) or increase his or her
Contributions. If specifically provided in the Offering, in addition to or instead of making Contributions by payroll deductions, a Participant may make Contributions through the payment by cash or check prior to a Purchase Date. 

(b)    During an Offering, a Participant may cease making Contributions and withdraw from the Offering by
delivering to the Company a withdrawal form provided by the Company. The Company may impose a deadline before a Purchase Date for withdrawing. Upon such withdrawal, such Participant’s Purchase Right in that Offering will immediately terminate
and the Company will distribute as soon as practicable to such Participant all of his or her accumulated but unused Contributions and such Participant’s Purchase Right in that Offering shall thereupon terminate. A Participant’s withdrawal
from that Offering will have no effect upon his or her eligibility to participate in any other Offerings under the Plan, but such Participant will be required to deliver a new enrollment form to participate in subsequent Offerings. 

(c)    Unless otherwise required by applicable law, Purchase Rights granted pursuant to any Offering under the Plan
will terminate immediately if the Participant either (i) is no longer an Employee for any reason or for no reason (subject to any post-employment participation period required by law) or (ii) is otherwise no longer eligible to participate.
The Company will distribute to such individual as soon as practicable all of his or her accumulated but unused Contributions. 

(d)    During a Participant’s lifetime, Purchase Rights will be exercisable only by such Participant. Purchase
Rights are not transferable by a Participant, except by will, by the laws of descent and distribution, or, if permitted by the Company, by a beneficiary designation as described in Section 10. 

(e)    Unless otherwise specified in the Offering or required by applicable law, the Company will have no
obligation to pay interest on Contributions. 
 8.    EXERCISE OF PURCHASE
RIGHTS. 
 (a)    On each Purchase Date, each Participant’s accumulated Contributions will
be applied to the purchase of shares of Common Stock, up to the maximum number of shares of Common Stock permitted by the Plan and the applicable Offering, at the purchase price specified in the Offering. No fractional shares will be issued unless
specifically provided for in the Offering. 
 (b)     Unless otherwise provided in the Offering, if any amount of
accumulated Contributions remains in a Participant’s account after the purchase of shares of Common Stock and such remaining amount is less than the amount required to purchase one share of Common Stock on the final Purchase Date of an
Offering, then such remaining amount will be held in such Participant’s account for the purchase of shares of Common Stock under the next Offering under the Plan, unless such Participant withdraws from or is not eligible to participate in such
next Offering, in which case such amount will be distributed to such Participant after the final Purchase Date without interest (unless the payment of interest is otherwise required by applicable law). If the amount of Contributions remaining in a

  
 5 

 
Participant’s account after the purchase of shares of Common Stock is at least equal to the amount required to purchase one (1) whole share of Common Stock on the final Purchase Date of
an Offering, then such remaining amount will be distributed in full to such Participant after the final Purchase Date of such Offering without interest. 

(c)    No Purchase Rights may be exercised to any extent unless the shares of Common Stock to be issued upon such
exercise under the Plan are covered by an effective registration statement pursuant to the Securities Act and the Plan is in material compliance with all applicable federal, state, foreign and other securities and other laws applicable to the Plan.
If on a Purchase Date the shares of Common Stock are not so registered or the Plan is not in such compliance, no Purchase Rights will be exercised on such Purchase Date, and the Purchase Date will be delayed until the shares of Common Stock are
subject to such an effective registration statement and the Plan is in material compliance, except that the Purchase Date will in no event be more than 6 months from the Offering Date. If, on the Purchase Date, as delayed to the maximum extent
permissible, the shares of Common Stock are not registered and the Plan is not in material compliance with all applicable laws, no Purchase Rights will be exercised and all accumulated but unused Contributions will be distributed to the Participants
without interest. 
 9.    COVENANTS OF THE COMPANY. 

The Company will seek to obtain from each U.S. federal or state, foreign or other regulatory commission or agency having jurisdiction over the
Plan such authority as may be required to grant Purchase Rights and issue and sell shares of Common Stock thereunder unless the Company determines, in its sole discretion, that doing so would cause the Company to incur costs that are unreasonable.
If, after commercially reasonable efforts, the Company is unable to obtain the authority that counsel for the Company deems necessary for the grant of Purchase Rights or the lawful issuance and sale of Common Stock under the Plan, and at a
commercially reasonable cost, the Company will be relieved from any liability for failure to grant Purchase Rights and/or to issue and sell Common Stock upon exercise of such Purchase Rights. 

10.    DESIGNATION OF BENEFICIARY. 

(a)    The Company may, but is not obligated to, permit a Participant to submit a form designating a beneficiary who
will receive any shares of Common Stock and/or Contributions from the Participant’s account under the Plan if the Participant dies before such shares and/or Contributions are delivered to the Participant. The Company may, but is not obligated
to, permit the Participant to change such designation of beneficiary. Any such designation and/or change must be on a form approved by the Company. 

(b)     If a Participant dies, and in the absence of a valid beneficiary designation, the Company will deliver any
shares of Common Stock and/or Contributions to the executor or administrator of the estate of the Participant. If no executor or administrator has been appointed (to the knowledge of the Company), the Company, in its sole discretion, may deliver
such shares of Common Stock and/or Contributions without interest (unless the payment of interest is otherwise required by applicable law) to the Participant’s spouse, dependents or relatives, or if no spouse, dependent or relative is known to
the Company, then to such other person as the Company may designate. 
 11.    ADJUSTMENTS UPON
CHANGES IN COMMON STOCK; CORPORATE TRANSACTIONS. 

(a)    In the event of a Capitalization Adjustment, the Board will appropriately and proportionately adjust:
(i) the class(es) and maximum number of securities subject to the Plan pursuant to Section 3(a), (ii) the class(es) and maximum number of securities by which the share reserve is to increase

  
 6 

 
automatically each year pursuant to Section 3(a), (iii) the class(es) and number of securities subject to, and the purchase price applicable to outstanding Offerings and Purchase Rights, and
(iv) the class(es) and number of securities that are the subject of the purchase limits under each ongoing Offering. The Board will make these adjustments, and its determination will be final, binding and conclusive. 

(b)    In the event of a Corporate Transaction, then: (i) any surviving corporation or acquiring corporation
(or the surviving or acquiring corporation’s parent company) may assume or continue outstanding Purchase Rights or may substitute similar rights (including a right to acquire the same consideration paid to the stockholders in the Corporate
Transaction) for outstanding Purchase Rights, or (ii) if any surviving or acquiring corporation (or its parent company) does not assume or continue such Purchase Rights or does not substitute similar rights for such Purchase Rights, then
the Participants’ accumulated Contributions will be used to purchase shares of Common Stock within ten business days prior to the Corporate Transaction under the outstanding Purchase Rights, and the Purchase Rights will terminate immediately
after such purchase. 
 12.    AMENDMENT, TERMINATION OR SUSPENSION
OF THE PLAN. 
 (a)    The Board may amend the Plan at any time
in any respect the Board deems necessary or advisable. However, except as provided in Section 11(a) relating to Capitalization Adjustments, stockholder approval will be required for any amendment of the Plan for which stockholder approval is
required by applicable law or listing requirements. 
 (b)    The Board may suspend or terminate the Plan at any
time. No Purchase Rights may be granted under the Plan while the Plan is suspended or after it is terminated. 

(c)    Any benefits, privileges, entitlements and obligations under any outstanding Purchase Rights granted before
an amendment, suspension or termination of the Plan will not be materially impaired by any such amendment, suspension or termination except (i) with the consent of the person to whom such Purchase Rights were granted, (ii) as necessary to
comply with any laws, listing requirements, or governmental regulations (including, without limitation, the provisions of Section 423 of the Code and the regulations and other interpretive guidance issued thereunder relating to Employee Stock
Purchase Plans) including without limitation any such regulations or other guidance that may be issued or amended after the date the Plan is adopted by the Board, or (iii) as necessary to obtain or maintain favorable tax, listing, or regulatory
treatment. To be clear, the Board may amend outstanding Purchase Rights without a Participant’s consent if such amendment is necessary to ensure that the Purchase Right and/or the Plan complies with the requirements of Section 423 of the
Code. 
 Notwithstanding anything in the Plan or any Offering Document to the contrary, the Board will be entitled to: (i) establish
the exchange ratio applicable to amounts withheld in a currency other than U.S. dollars; (ii) permit Contributions in excess of the amount designated by a Participant in order to adjust for mistakes in the Company’s processing of properly
completed Contribution elections; (iii) establish reasonable waiting and adjustment periods and/or accounting and crediting procedures to ensure that amounts applied toward the purchase of Common Stock for each Participant properly correspond
with amounts withheld from the Participant’s Contributions; (iv) amend any outstanding Purchase Rights or clarify any ambiguities regarding the terms of any Offering to enable the Purchase Rights to qualify under and/or comply with
Section 423 of the Code; and (v) establish other limitations or procedures as the Board determines in its sole discretion advisable that are consistent with the Plan. The actions of the Board pursuant to this paragraph will not be
considered to alter or impair any Purchase Rights granted under an Offering as they are part of the initial terms of each Offering and the Purchase Rights granted under each Offering. 

  
 7 

 13.    EFFECTIVE DATE OF
PLAN. 
 The Plan will become effective immediately prior to and contingent upon the IPO Date. No Purchase Rights will be
exercised unless and until the Plan has been approved by the stockholders of the Company, which approval must be within 12 months before or after the date the Plan is adopted (or if required under Section 12(a) above, materially amended) by the
Board. 
 14.    MISCELLANEOUS PROVISIONS. 

(a)    Proceeds from the sale of shares of Common Stock pursuant to Purchase Rights will constitute general funds of
the Company. 
 (b)    A Participant will not be deemed to be the holder of, or to have any of the rights of a
holder with respect to, shares of Common Stock subject to Purchase Rights unless and until the Participant’s shares of Common Stock acquired upon exercise of Purchase Rights are recorded in the books of the Company (or its transfer agent). 

(c)    The Plan and Offering do not constitute an employment contract. Nothing in the Plan or in the Offering will
in any way alter the at will nature of a Participant’s employment or be deemed to create in any way whatsoever any obligation on the part of any Participant to continue in the employ of the Company or a Related Corporation, or on the part of
the Company or a Related Corporation to continue the employment of a Participant. 
 (d)    The provisions of the
Plan will be governed by the laws of the State of Delaware without resort to that state’s conflict of laws rules. 

15.    DEFINITIONS. 

As used in the Plan, the following definitions will apply to the capitalized terms indicated below: 

(a)    “Board” means the Board of Directors of the Company. 

(b)    “Capital Stock” means each and every class of common stock of the Company,
regardless of the number of votes per share. 
 (c)    “Capitalization Adjustment” means
any change that is made in, or other events that occur with respect to, the Common Stock subject to the Plan or subject to any Purchase Right after the date the Plan is adopted by the Board without the receipt of consideration by the Company through
merger, consolidation, reorganization, recapitalization, reincorporation, stock dividend, dividend in property other than cash, large nonrecurring cash dividend, stock split, liquidating dividend, combination of shares, exchange of shares, change in
corporate structure or other similar equity restructuring transaction, as that term is used in Financial Accounting Standards Board Accounting Standards Codification Topic 718 (or any successor thereto). Notwithstanding the foregoing, the conversion
of any convertible securities of the Company will not be treated as a Capitalization Adjustment. 

(d)    “Code” means the Internal Revenue Code of 1986, as amended, including any
applicable regulations and guidance thereunder. 
 (e)    “Committee” means
a committee of one or more members of the Board to whom authority has been delegated by the Board in accordance with Section 2(c). 

  
 8 

 (f)    “Common Stock” means, as of the
IPO Date, the common stock of the Company. 
 (g)    “Company” means Keros Therapeutics,
Inc., a Delaware corporation. 
 (h)    “Contributions” means the payroll deductions and
other additional payments specifically provided for in the Offering that a Participant contributes to fund the exercise of a Purchase Right. A Participant may make additional payments into his or her account if specifically provided for in the
Offering, and then only if the Participant has not already had the maximum permitted amount withheld during the Offering through payroll deductions. 

(i)    “Corporate Transaction” means the consummation, in a single transaction or in a
series of related transactions, of any one or more of the following events: 
 (i)    a sale or other
disposition of all or substantially all, as determined by the Board in its sole discretion, of the consolidated assets of the Company and its subsidiaries; 

(ii)    a sale or other disposition of more than 50% of the outstanding securities of the Company; 

(iii)    a merger, consolidation or similar transaction following which the Company is not the surviving
corporation; or 
 (iv)    a merger, consolidation or similar transaction following which the Company is the
surviving corporation but the shares of Common Stock outstanding immediately preceding the merger, consolidation or similar transaction are converted or exchanged by virtue of the merger, consolidation or similar transaction into other property,
whether in the form of securities, cash or otherwise. 
 (j)    “Director” means a
member of the Board. 
 (k)    “Eligible Employee” means an Employee who meets the
requirements set forth in the document(s) governing the Offering for eligibility to participate in the Offering, provided that such Employee also meets the requirements for eligibility to participate set forth in the Plan. 

(l)    “Employee” means any person, including an Officer or Director, who is
“employed” for purposes of Section 423(b)(4) of the Code by the Company or a Related Corporation. However, service solely as a Director, or payment of a fee for such services, will not cause a Director to be considered an
“Employee” for purposes of the Plan. 
 (m)    “Employee Stock Purchase
Plan” means a plan that grants Purchase Rights intended to be options issued under an “employee stock purchase plan,” as that term is defined in Section 423(b) of the Code. 

(n)    “Exchange Act” means the Securities Exchange Act of 1934, as amended and the
rules and regulations promulgated thereunder. 
 (o)    “Fair Market Value” means, as of
any date, the value of the Common Stock determined as follows: 
 (i)    If the Common Stock is listed on any
established stock exchange or traded on any established market, the Fair Market Value of a share of Common Stock will be, unless otherwise 

  
 9 

 
determined by the Board, the closing sales price for such stock as quoted on such exchange or market (or the exchange or market with the greatest volume of trading in the Common
Stock) on the date of determination, as reported in such source as the Board deems reliable. Unless otherwise provided by the Board, if there is no closing sales price for the Common Stock on the date of determination, then the Fair
Market Value will be the closing sales price on the last preceding date for which such quotation exists. 

(ii)    In the absence of such markets for the Common Stock, the Fair Market Value will be determined by the Board
in good faith in compliance with applicable laws and in a manner that complies with Sections 409A of the Code. 

(iii)    Notwithstanding the foregoing, for any Offering that commences on the IPO Date, the Fair Market Value of
the shares of Common Stock on the Offering Date will be the price per share at which shares are first sold to the public in the Company’s initial public offering as specified in the final prospectus for that initial public offering. 

(p)    “IPO Date” means the date of the underwriting agreement between the Company
and the underwriter(s) managing the initial public offering of the Common Stock, pursuant to which the Common Stock is priced for the initial public offering. 

(q)    “Offering” means the grant to Eligible Employees of Purchase Rights, with the
exercise of those Purchase Rights automatically occurring at the end of one or more Purchase Periods. The terms and conditions of an Offering will generally be set forth in the “Offering Document” approved by the Board for
that Offering. 
 (r)    “Offering Date” means a date selected by the Board for an
Offering to commence. 
 (s)    “Officer” means a person who is an officer
of the Company or a Related Corporation within the meaning of Section 16 of the Exchange Act. 

(t)    “Participant” means an Eligible Employee who holds an outstanding Purchase
Right. 
 (u)    “Plan” means this Keros Therapeutics, Inc. 2020 Employee Stock
Purchase Plan, as amended from time to time. 
 (v)    “Purchase Date” means one
or more dates during an Offering selected by the Board on which Purchase Rights will be exercised and on which purchases of shares of Common Stock will be carried out in accordance with such Offering. 

(w)    “Purchase Period” means a period of time specified within an Offering, generally
beginning on the Offering Date or on the first Trading Day following a Purchase Date, and ending on a Purchase Date. An Offering may consist of one or more Purchase Periods. 

(x)    “Purchase Right” means an option to purchase shares of Common Stock granted
pursuant to the Plan. 
 (y)    “Related Corporation” means any “parent
corporation” or “subsidiary corporation” of the Company whether now or subsequently established, as those terms are defined in Sections 424(e) and (f), respectively, of the Code. 

(z)    “Securities Act” means the Securities Act of 1933, as amended. 

  
 10 

 (aa)    “Subsidiary” means, with respect
to the Company, (i) any corporation of which more than fifty percent (50%) of the outstanding capital stock having ordinary voting power to elect a majority of the board of directors of such corporation (irrespective of whether, at the time,
stock of any other class or classes of such corporation will have or might have voting power by reason of the happening of any contingency) is at the time, directly or indirectly, Owned by the Company, and (ii) any partnership, limited
liability company or other entity in which the Company has a direct or indirect interest (whether in the form of voting or participation in profits or capital contribution) of more than fifty percent (50%). For purposes of the foregoing clause (i),
the Company will be deemed to “Own” or have “Owned” such securities if the Company, directly or indirectly, through any contract, arrangement, understanding, relationship or otherwise, has or shares voting power, which includes
the power to vote or to direct the voting, with respect to such securities. 
 (bb)    “Trading
Day” means any day on which the exchange(s) or market(s) on which shares of Common Stock are listed, including but not limited to the NYSE, Nasdaq Global Select Market, the Nasdaq Global Market, the Nasdaq Capital Market or any
successors thereto, is open for trading. 

  
 11

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00306-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00306-of-00352.parquet"}]]