# EDGAR Filing Document

**Accession Number:** 0001501697
**File Stem:** 0000000000-25-009968
**Filing Date:** 2025-9
**Character Count:** 2314
**Document Hash:** 4ceee6177b973130dc4b8e8140301a11
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000000000-25-009968.hdr.sgml**: 20251121

**ACCESSION NUMBER**: 0000000000-25-009968

**CONFORMED SUBMISSION TYPE**: UPLOAD

**PUBLIC DOCUMENT COUNT**: 2

**FILED AS OF DATE**: 20250915

**FILED FOR**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** X4 Pharmaceuticals, Inc
- **CENTRAL INDEX KEY:** 0001501697
- **STANDARD INDUSTRIAL CLASSIFICATION:** BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 273181608
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** UPLOAD
- **SEC FILE NUMBER:** 333-290158

**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
**PUBLIC REFERENCE ACCESSION NUMBER**: 0001501697-25-000017

## Text-Extract

```

                                                           September 15, 2025

Adam Craig
Executive Chairman
X4 Pharmaceuticals, Inc.
61 North Beacon Street, 4th Floor
Boston, MA 02134

       Re: X4 Pharmaceuticals, Inc.
           Registration Statement on Form S-3
           Filed September 10, 2025
           File No. 333-290158
Dear Adam Craig:

       This is to advise you that we have not reviewed and will not review your
registration
statement.

        Please refer to Rules 460 and 461 regarding requests for acceleration.
We remind you
that the company and its management are responsible for the accuracy and
adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action
by the staff.

       Please contact Jessica Dickerson at 202-551-8013 with any questions.

                                                           Sincerely,

                                                           Division of
Corporation Finance
                                                           Office of Life
Sciences
cc:   Ryan A. Murr, Esq.

```

### Attached PDF Documents

**Attachment 1:** `filename1`

_No text found in this document._