SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* ARCH Venture Partners IX, LLC (Last) (First) (Middle) 8755 W. HIGGINS ROAD SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 02/07/2019	3. Issuer Name and Ticker or Trading Symbol Gossamer Bio, Inc. [ GOSS ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series A Preferred Stock	(1)	(1)	Common Stock	3,682,539	$0.00	I	See footnotes(2)(3)
Series A Preferred Stock	(1)	(1)	Common Stock	3,682,539	$0.00	I	See footnotes(3)(4)
Series B Preferred Stock	(5)	(5)	Common Stock	345,419	$0.00	I	See footnotes(2)(3)
Series B Preferred Stock	(5)	(5)	Common Stock	345,419	$0.00	I	See footnotes(3)(4)

1. Name and Address of Reporting Person* ARCH Venture Partners IX, LLC (Last) (First) (Middle) 8755 W. HIGGINS ROAD SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ARCH Venture Partners IX, L.P. (Last) (First) (Middle) 8755 W. HIGGINS ROAD, SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ARCH Venture Partners IX Overage, L.P. (Last) (First) (Middle) 8755 W. HIGGINS ROAD, SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ARCH Venture Fund IX, L.P. (Last) (First) (Middle) 8755 W. HIGGINS ROAD, SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ARCH Venture Fund IX Overage, L.P. (Last) (First) (Middle) 8755 W. HIGGINS ROAD, SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* NELSEN ROBERT (Last) (First) (Middle) C/O ARCH VENTURE PARTNERS IX, LLC 8755 W. HIGGINS ROAD, SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* CRANDELL KEITH (Last) (First) (Middle) C/O ARCH VENTURE PARTNERS IX, LLC 8755 W. HIGGINS ROAD, SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* BYBEE CLINTON (Last) (First) (Middle) C/O ARCH VENTURE PARTNERS IX, LLC 8755 W. HIGGINS ROAD, SUITE 1025 (Street) CHICAGO IL 60631 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. Each of the 16,571,429 and 16,571,428 shares of Series A Preferred Stock held by ARCH Venture Fund IX, L.P. ("ARCH IX") and ARCH Venture Fund IX Overage, L.P. ("ARCH Overage"), respectively, is convertible, at any time, at the holder's election, at a ratio of 4.5 to one share of the Issuer's common stock. In addition, effective immediately prior to the closing of the Issuer's initial public offering of its common stock, for no additional consideration, each share of Series A Preferred Stock will automatically convert at a ratio of 4.5 to one share of the Issuer's common stock. The Series A Preferred Stock has no expiration date.

2. These shares are directly held by ARCH IX. ARCH Venture Partners IX, L.P. ("GPLP"), as the sole general partner of ARCH IX, may be deemed to beneficially own the shares held by ARCH IX. ARCH Venture Partners IX, LLC ("GPLLC"), as the sole general partner of GPLP, may be deemed to beneficially own the shares held by GPLP. As managing directors of GPLLC, each of Keith Crandell, Clinton Bybee and Robert Nelsen (the "ARCH Managing Directors"), may be deemed to beneficially own the shares held by GPLLC.

3. Each of GPLP, Overage GPLP, GPLLC and the ARCH Managing Directors disclaims beneficial ownership of the securities reported herein, except to the extent of their pecuniary interest therein, if any.

4. These shares are directly held by ARCH Overage. ARCH Venture Partners IX Overage, L.P. ("Overage GPLP"), as the sole general partner of ARCH Overage, may be deemed to beneficially own the shares held by ARCH Overage. GPLLC, as the sole general partner of Overage GPLP, may be deemed to beneficially own the shares held by Overage GPLP. As managing directors of GPLLC, each of the ARCH Managing Directors may be deemed to beneficially own the shares held by GPLLC.

5. Each of the 1,554,388 and 1,554,388 shares of Series B Preferred Stock held by ARCH IX and ARCH Overage, respectively, is convertible, at any time, at the holder's election, at a ratio of 4.5 to one share of the Issuer's common stock. In addition, effective immediately prior to the closing of the Issuer's initial public offering of its common stock, for no additional consideration, each share of Series B Preferred Stock will automatically convert at a ratio of 4.5 to one share of the Issuer's common stock. The Series B Preferred Stock has no expiration date.

Remarks:

Exhibit 24 - Power of Attorney

	ARCH Venture Partners IX, LLC, By: /s/ Mark McDonnell, as Attorney-in-Fact for Robert Nelsen, Managing Director	02/07/2019
	ARCH Venture Partners IX, L.P., By: ARCH Venture Partners IX, LLC, its General Partner, By: /s/ Mark McDonnell, as Attorney-in-Fact for Keith Crandell, Managing Director	02/07/2019
	ARCH Venture Partners IX Overage, L.P., By: ARCH Venture Partners IX, LLC, its General Partner, By: /s/ Mark McDonnell, as Attorney-in-Fact for Keith Crandell, Managing Director	02/07/2019
	ARCH Venture Fund IX, L.P., By: ARCH Venture Partners IX, L.P., its General Partner, By: ARCH Venture Partners IX, LLC, its General Partner, By: /s/ Mark McDonnell, as Attorney-in-Fact for Keith Crandell, Managing Director	02/07/2019
	ARCH Venture Fund IX Overage, L.P., By: ARCH Venture Partners IX Overage, L.P., its General Partner, By: ARCH Venture Partners IX, LLC, its General Partner, By: /s/ Mark McDonnell, as Attorney-in-Fact for Keith Crandell, Managing Director	02/07/2019
	Robert Nelsen, Managing Director, By: /s/ Mark McDonnell, as Attorney-in-Fact	02/07/2019
	Keith Crandell, Managing Director, By: /s/ Mark McDonnell, as Attorney-in-Fact	02/07/2019
	Clinton Bybee, Managing Director, By: /s/ Mark McDonnell, as Attorney-in-Fact	02/07/2019
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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