Statement of Changes in Beneficial Ownership (4)

FORM 4 [ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person ^* Flagship Ventures Fund IV General Partner LLC	2. Issuer Name and Ticker or Trading Symbol Seres Therapeutics, Inc. [ MCRB ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below)
(Last) (First) (Middle) 55 CAMBRIDGE PARKWAY, SUITE 800E	3. Date of Earliest Transaction (MM/DD/YYYY) 11/23/2020
(Street) CAMBRIDGE, MA 02142 (City) (State) (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _ X _ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	11/23/2020		J⁽¹⁾		3587820	D	$0.00	4434600	I	See Footnote ⁽²⁾
Common Stock	11/23/2020		J⁽¹⁾		642180	D	$0.00	1283282	I	See Footnote ⁽³⁾
Common Stock	11/23/2020		J⁽¹⁾		966234	D	$0.00	0	I	See Footnote ⁽⁴⁾
Common Stock	11/23/2020		J⁽⁵⁾		1186310	D	$0.00	3258134	I	See Footnote ⁽⁶⁾
Common Stock	11/23/2020		J⁽⁷⁾		1481481	D	$0.00	2962963	I	See Footnote ⁽⁸⁾
Common Stock	11/23/2020		J⁽⁷⁾		43154	D	$0.00	0	I	See Footnote ⁽⁹⁾
Common Stock								2734994	I	See Footnote ⁽¹⁰⁾
Common Stock								376018	I	See Footnote ⁽¹¹⁾

*Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)*
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)			11. Nature of Indirect Beneficial Ownership (Instr. 4)

Explanation of Responses:
(1)	On November 23, 2020, Flagship Ventures Fund IV, L.P. ("Flagship Fund IV") and Flagship Ventures Fund IV-Rx, L.P. ("Flagship Fund IV-Rx") distributed to its limited partners and sole general partner, Flagship Ventures Fund IV General Partner, LLC ("Flagship Fund IV GP"), pro rata and without consideration, 3,587,820 shares and 642,180 shares, respectively, of the Issuer's common stock. Flagship Fund IV GP, in turn, distributed to its members, pro rata and without consideration, the 837,782 shares and 128,452 shares it received from Flagship Fund IV and Flagship Fund IV-Rx, respectively. Noubar B. Afeyan, Ph.D. received 335,171 shares through Flagship Fund IV GP's distribution. The aforementioned distributions were made in accordance with the exemptions afforded by Rule 16a-13 and Rule 16a-9 of the Securities Exchange Act of 1934, as amended.
(2)	Shares held by Flagship Fund IV. Flagship Fund IV GP is the general partner of Flagship Fund IV. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Edwin M. Kania, Jr. is retired both from Flagship Pioneering and as a manager of Flagship Fund IV GP.
(3)	Shares held by Flagship Fund IV-Rx. Flagship Fund IV GP is the general partner of Flagship Fund IV-Rx. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV-Rx disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
(4)	Shares held by Flagship Fund IV GP. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV GP disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
(5)	On November 23, 2020, Nutritional Health LTP Fund, L.P. ("Nutritional LTP") distributed to its limited partners, pro rata and without consideration, 1,186,310 shares of the Issuer's common stock. The aforementioned distribution was made in accordance with the exemptions afforded by Rule 16a-13 and Rule 16a-9 of the Securities Exchange Act of 1934, as amended.
(6)	Shares held by Nutritional LTP. Nutritional Health LTP Fund General Partner LLC ("Nutritional LTP GP") is the general partner of Nutritional LTP. Noubar B. Afeyan Ph.D. is the sole member and manager of Nutritional LTP GP. Each of the reporting persons except for Nutritional LTP disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
(7)	On November 23, 2020, Flagship Pioneering Fund VI, L.P. ("Flagship Fund VI") distributed to its limited partners and sole general partner, Flagship Pioneering Fund VI General Partner LLC ("Flagship Fund VI GP"), pro rata and without consideration, 1,481,481 shares of the Issuer's common stock. Flagship Fund VI GP, in turn, distributed to its members, pro rata and without consideration, the 43,154 shares it received from Flagship Fund VI. Each of Noubar B. Afeyan, Ph.D. and a trust for the benefit of Dr. Afeyan's children received 12,853 shares through Flagship Fund VI GP's distribution. The aforementioned distributions were made in accordance with the exemptions afforded by Rule 16a-13 and Rule 16a-9 of the Securities Exchange Act of 1934, as amended.
(8)	Shares held by Flagship Fund VI. Flagship Fund VI GP is the general partner of Flagship Fund VI. Flagship Pioneering, Inc. ("Flagship Pioneering") is the manager of Flagship Fund VI GP. Noubar B. Afeyan Ph.D. is the CEO, sole shareholder and director of Flagship Pioneering. Each of the reporting persons except Flagship Fund VI disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
(9)	Shares held by Flagship Fund VI GP. Flagship Pioneering is the manager of Flagship Fund VI GP. Noubar B. Afeyan Ph.D. is the CEO, sole shareholder and director of Flagship Pioneering. Each of the reporting persons except Flagship Fund VI GP disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
(10)	Shares held by Flagship VentureLabs IV LLC ("VentureLabs IV"). Flagship Fund IV is a member of VentureLabs IV and also serves as its manager. Each of the reporting persons except VentureLabs IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
(11)	Shares held by Noubar B. Afeyan, Ph.D. Each of the reporting persons except for Noubar B. Afeyan, Ph.D. disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Includes 12,853 shares held through a trust for the benefit of Dr. Afeyan's children. Dr. Afeyan disclaims Section 16 beneficial ownership of these shares except to the extent of his pecuniary interest therein, and this report shall not be deemed an admission that the reporting person is the beneficial owner of such shares for Section 16 or any other purpose.

Reporting Owners
Reporting Owner Name / Address	Relationships
Reporting Owner Name / Address	Director	10% Owner	Officer	Other
Flagship Ventures Fund IV General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
Flagship Ventures Fund IV, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
Flagship Ventures Fund IV-Rx, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
Nutritional Health LTP Fund General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
Nutritional Health LTP Fund, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
Flagship Pioneering Inc. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
Flagship Pioneering Fund VI General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
Flagship Pioneering Fund VI, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X
AFEYAN NOUBAR 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE, MA 02142		X

Signatures
Flagship Ventures Fund IV General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager		11/25/2020
^**Signature of Reporting Person		Date
Flagship Ventures Fund IV, L.P., By: Flagship Ventures Fund IV General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager		11/25/2020
^**Signature of Reporting Person		Date
Flagship Ventures Fund IV-Rx, L.P., By: Flagship Ventures Fund IV General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager		11/25/2020
^**Signature of Reporting Person		Date
Nutritional Health LTP Fund General Partner LLC, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager		11/25/2020
^**Signature of Reporting Person		Date
Nutritional Health LTP Fund, L.P., By: Nutritional Health LTP Fund General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: Manager		11/25/2020
^**Signature of Reporting Person		Date
Flagship Pioneering, Inc., By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: CEO, Sole Shareholder & Director		11/25/2020
^**Signature of Reporting Person		Date
Flagship Pioneering Fund VI General Partner LLC, By: Flagship Pioneering, Inc., its manager, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: CEO, Sole Shareholder & Director		11/25/2020
^**Signature of Reporting Person		Date
Flagship Pioneering Fund VI, L.P., By: Flagship Pioneering Fund VI General Partner LLC, its general partner, By: Flagship Pioneering, Inc., its manager, By: /s/ Noubar B. Afeyan, Name: Noubar B. Afeyan, Ph.D., Title: CEO, Sole Shareholder & Director		11/25/2020
^**Signature of Reporting Person		Date
Noubar B. Afeyan, Ph.D., by: /s/ Noubar B. Afeyan		11/25/2020
^**Signature of Reporting Person		Date