Bain Capital Life Sciences Investors 13F-HR Quarterly holdings report by institutional manager

The Securities and Exchange Commission has not necessarily reviewed the information in this filing and has not determined if it is accurate and complete.
The reader should not assume that the information is accurate and complete.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 13F

FORM 13F COVER PAGE

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Report for the Calendar Year or Quarter Ended: 12-31-2023

Check here if Amendment	Amendment Number:
This Amendment (Check only one.):	is a restatement.
	adds new holdings entries.

Institutional Investment Manager Filing this Report:
Name:	Bain Capital Life Sciences Investors, LLC
Address:	200 Clarendon Street
	Boston, MA  02116
Form 13F File Number:	028-18477

The institutional investment manager filing this report and the person by whom it is signed hereby represent that the person signing the report is authorized to submit it, that all information contained herein is true, correct and complete, and that it is understood that all required items, statements, schedules, lists, and tables, are considered integral parts of this form.

Person Signing this Report on Behalf of Reporting Manager:
Name:	Adam Koppel
Title:	Partner of Bain Capital Life Sciences Investors, LLC
Phone:	617-516-2000
Signature, Place, and Date of Signing:
/s/ Adam Koppel		Boston,  MA	02-13-2024
[Signature]		[City, State]	[Date]
Bain Capital Life Sciences Investors, LLC ("BCLSI") is (i) the general partner of Bain Capital Life Sciences Partners, LP, which is the general partner of Bain Capital Life Sciences Fund, L.P., (ii) the general partner of BC SW, LP, (iii) the manager of Bain Capital Life Sciences Investors II, LLC, which is the general partner of Bain Capital Life Sciences Fund II, L.P., which is the manager of BCLS II Investco (GP), LLC, which is the general partner of BCLS II Investco, LP, and (iv) the manager of Bain Capital Life Sciences III General Partner, LLC, which is the general partner of Bain Capital Life Sciences Fund III, L.P., which is the sole member of Bain Capital Life Sciences Opportunities III GP, LLC, which is the general partner of Bain Capital Life Sciences Opportunities III, LP. The shares of Annexon, Inc. ("ANNX") are as reported on Amend. No. 3 to Schedule 13G filed by affiliates of BCLSI on 2/13/24 and reflect the exercise of securities held by such persons for ANNX common stock, after giving effect to 9.99% conversion blockers. As of 12/31/23, such persons held 5,701,926 shares of ANNX common stock. The shares of Savara Inc. ("SVRA") are as reported on Amend. No. 2 to Schedule 13D filed by affiliates of BCLSI on 7/19/23 and reflect the exercise of securities held by such persons for SVRA common stock, after giving effect to 9.99% conversion blockers. As of 12/31/23, such persons held 6,913,208 shares of SVRA common stock. The shares of Syros Pharmaceuticals, Inc. ("SYRS") are as reported on Amend. No. 3 to Schedule 13G filed by affiliates of BCLSI on 2/13/24 and reflect the exercise of securities held by such persons for SYRS common stock, after giving effect to 9.99% conversion blockers. As of 12/31/23, such persons held 1,230,857 shares of SYRS common stock. The shares of X4 Pharmaceuticals, Inc. ("XFOR") are as reported on Amend. No. 3 to Schedule 13G filed by affiliates of BCLSI on 2/13/24 and reflect the exercise of securities held by such persons for XFOR common stock, after giving effect to 9.99% conversion blockers. As of 12/31/23, such persons held 14,879,809 shares of XFOR common stock.

Report Type (Check only one.):
X	13F HOLDINGS REPORT. (Check here if all holdings of this reporting manager are reported in this report.)
	13F NOTICE. (Check here if no holdings reported are in this report, and all holdings are reported by other reporting manager(s).)
	13F COMBINATION REPORT. (Check here if a portion of the holdings for this reporting manager are reported in this report and a portion are reported by other reporting manager(s).)

Form 13F Summary Page
	Report Summary:
	Number of Other Included Managers:	11
	Form 13F Information Table Entry Total:	27
	Form 13F Information Table Value Total:	1,043,257,107
		(thousands)

List of Other Included Managers:
Provide a numbered list of the name(s) and Form 13F file number(s) of all institutional investment managers with respect to which this report is filed, other than the manager filing this report.
[If there are no entries in this list, state “NONE” and omit the column headings and list entries.]
	No.	Form 13F File Number	Name
	1	28-18476	Bain Capital Life Sciences Partners, LP
	2	28-18478	Bain Capital Life Sciences Fund, L.P.
	3	28-20270	BC SW, LP
	4	28-20816	Bain Capital Life Sciences Investors II, LLC
	5	28-20814	Bain Capital Life Sciences Fund II, L.P.
	6	28-22976	BCLS II Investco (GP), LLC
	7	28-22978	BCLS II Investco, LP
	8	28-22975	Bain Capital Life Sciences III General Partner, LLC
	9	28-22979	Bain Capital Life Sciences Fund III, L.P.
	10	28-22968	Bain Capital Life Sciences Opportunities III GP, LLC
	11	28-22966	Bain Capital Life Sciences Opportunities III, LP