    <SEC-DOCUMENT>0001628280-22-001252-index.html : 20220125
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    <ACCEPTANCE-DATETIME>20220125171352
    ACCESSION NUMBER:		0001628280-22-001252
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		14
    CONFORMED PERIOD OF REPORT:	20220125
    ITEM INFORMATION:		Results of Operations and Financial Condition
    ITEM INFORMATION:		Regulation FD Disclosure
    ITEM INFORMATION:		Other Events
    FILED AS OF DATE:		20220125
    DATE AS OF CHANGE:		20220125

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			X4 Pharmaceuticals, Inc
    		CENTRAL INDEX KEY:			0001501697
    		STANDARD INDUSTRIAL CLASSIFICATION:	BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
    		IRS NUMBER:				273181608
    		STATE OF INCORPORATION:			DE
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	001-38295
    		FILM NUMBER:		22554734

    	BUSINESS ADDRESS:
    		STREET 1:		61 NORTH BEACON STREET
    		STREET 2:		4TH FLOOR
    		CITY:			BOSTON
    		STATE:			MA
    		ZIP:			02134
    		BUSINESS PHONE:		857-529-8300

    	MAIL ADDRESS:
    		STREET 1:		61 NORTH BEACON STREET
    		STREET 2:		4TH FLOOR
    		CITY:			BOSTON
    		STATE:			MA
    		ZIP:			02134

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	Arsanis, Inc.
    		DATE OF NAME CHANGE:	20100920
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    <DOCUMENT>
    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>xfor-20220125.htm
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    <TEXT>
    Document 1 - file: xfor-20220125.htm

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    <FILENAME>ex991jan252022.htm
    <DESCRIPTION>EX-99.1
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    Document 2 - file: ex991jan252022.htm

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    <SEQUENCE>3
    <FILENAME>xfor-20220125.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
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    <FILENAME>image_0a.jpg
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    <FILENAME>Financial_Report.xlsx
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    <TEXT>
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    <SEQUENCE>12
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    <TYPE>JSON
    <SEQUENCE>14
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    <TYPE>ZIP
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