X4 Pharmaceuticals amendment to Schedule 13G/A reports that Perceptive Advisors, Joseph Edelman and Perceptive Life Sciences Master Fund, Ltd. each beneficially own 6,889,163 shares, representing 7.3% of Common Stock based on 94,319,696 outstanding shares as of May 1, 2026. The filing states the Master Fund directly holds 6,737,648 shares and 151,515 Warrants immediately exercisable for Common Stock, subject to a Beneficial Ownership Limitation that caps ownership at 9.99%.
The reporting persons disclose shared voting and dispositive power over the reported shares and note Perceptive Advisors acts as investment manager to the Master Fund, with Joseph Edelman as managing member.
Positive
None.
Negative
None.
Insights
Perceptive group reports a 7.3% stake with exercisable warrants capped by a 9.99% limit.
The filing lists shared voting and dispositive power over 6,889,163 shares and discloses the Master Fund's direct holding of 6,737,648 shares plus 151,515 Warrants exercisable subject to the Beneficial Ownership Limitation. This clarifies legal exercise constraints and the group's managerial relationship.
Cash‑flow treatment for warrant exercises and timing are not detailed here; subsequent filings would show any exercises or changes in ownership percentages.
Key Figures
Shares beneficially owned:6,889,163 sharesPercent of class:7.3%Shares outstanding:94,319,696 shares+3 more
6 metrics
Shares beneficially owned6,889,163 sharesreported beneficial ownership by each Reporting Person
Percent of class7.3%based on 94,319,696 outstanding shares as of May 1, 2026
Shares outstanding94,319,696 sharesoutstanding shares used to calculate percentage as of <date>May 1, 2026</date>
Master Fund direct shares6,737,648 sharesMaster Fund direct holdings disclosed in the filing
Warrants exercisable151,515 Warrantsimmediately exercisable for Common Stock subject to Beneficial Ownership Limitation
Beneficial Ownership Limit9.99%exercise cap for the Warrants as stated in the filing
Key Terms
Beneficial Ownership Limitation, Warrants, Shared dispositive power
3 terms
Beneficial Ownership Limitationregulatory
"The terms of the Warrants provide that the Warrants may not be exercised if, after such exercise, the Reporting Persons would beneficially own... 9.99%"
A beneficial ownership limitation is a rule that caps the percentage of a company’s shares an investor can be treated as owning or controlling for voting, regulatory or tax purposes. It matters to investors because it can restrict how many shares a person or group can buy or vote, affect takeover chances, and influence share liquidity and value — like a speed limit that prevents any single driver from taking over the whole road.
Warrantsfinancial
"The Master Fund directly holds 6,737,648 shares of Common Stock and 151,515 Warrants immediately exercisable for shares of Common Stock"
Warrants are special documents that give you the right to buy a company's stock at a set price before a certain date. They are often used as a way for companies to attract investors or raise money, and their value can increase if the company's stock price goes up.
Shared dispositive powerregulatory
"Shared Dispositive Power 6,889,163.00"
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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
(Amendment No. 1)
X4 PHARMACEUTICALS, INC.
(Name of Issuer)
Common Stock, par value $0.001 per share
(Title of Class of Securities)
98420X202
(CUSIP Number)
03/31/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
98420X202
1
Names of Reporting Persons
Perceptive Advisors LLC
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,889,163.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,889,163.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,889,163.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
7.3 %
12
Type of Reporting Person (See Instructions)
IA
SCHEDULE 13G
CUSIP Number(s):
98420X202
1
Names of Reporting Persons
Joseph Edelman
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,889,163.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,889,163.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,889,163.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
7.3 %
12
Type of Reporting Person (See Instructions)
IN
SCHEDULE 13G
CUSIP Number(s):
98420X202
1
Names of Reporting Persons
Perceptive Life Sciences Master Fund, Ltd.
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
CAYMAN ISLANDS
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,889,163.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,889,163.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,889,163.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
7.3 %
12
Type of Reporting Person (See Instructions)
CO
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
X4 PHARMACEUTICALS, INC.
(b)
Address of issuer's principal executive offices:
61 North Beacon Street, 4th Floor, Boston, Massachusetts
Item 2.
(a)
Name of person filing:
The names of the persons filing this report (collectively, the "Reporting Persons") with respect to shares of Common Stock, par value $0.001 per share (the "Common Stock") of X4 PHARMACEUTICALS, INC. (the "Issuer") are:
Perceptive Advisors LLC ("Perceptive Advisors")
Joseph Edelman ("Mr. Edelman")
Perceptive Life Sciences Master Fund, Ltd. (the "Master Fund")
(b)
Address or principal business office or, if none, residence:
The address of the principal business office of each of the Reporting Persons is:
51 Astor Place, 10th Floor
New York, NY 10003
(c)
Citizenship:
Perceptive Advisors is a Delaware limited liability company
Mr. Edelman is a United States citizen
The Master Fund is a Cayman Islands corporation
(d)
Title of class of securities:
Common Stock, par value $0.001 per share
(e)
CUSIP No.:
98420X202
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
The information required by this item with respect to each Reporting Person is set forth in Rows 5 through 9 and 11 of the cover pages to this Schedule 13G. The ownership percentages reported are based on 94,319,696 outstanding shares of Common Stock as of May 1, 2026, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on May 6, 2026.
Neither Perceptive Advisors nor Mr. Edelman directly hold any shares of Common Stock or any Warrants. The Master Fund directly holds 6,737,648 shares of Common Stock and 151,515 Warrants immediately exercisable for shares of Common Stock, subject to the Beneficial Ownership Limitation (as defined below). The terms of the Warrants provide that the Warrants may not be exercised if, after such exercise, the Reporting Persons would beneficially own, as determined in accordance with Section 13(d) if the Securities Exchange Act of 1934, as amended, more than 9.99% of the shares of Common Stock then issued and outstanding (the "Beneficial Ownership Limitation"). As of the date hereof, the Beneficial Ownership Limitation permits the Reporting Persons to exercise Warrants for an aggregate of 151,515 shares of Common Stock. Perceptive Advisors serves as the investment manager to the Master Fund. Mr. Edelman is the managing member of Perceptive Advisors.
(b)
Percent of class:
Perceptive Advisors: 7.3%
Mr. Edelman: 7.3%
Master Fund: 7.3%
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
Perceptive Advisors: 0
Mr. Edelman: 0
Master Fund: 0
(ii) Shared power to vote or to direct the vote:
Perceptive Advisors: 6,889,163
Mr. Edelman: 6,889,163
Master Fund: 6,889,163
(iii) Sole power to dispose or to direct the disposition of:
Perceptive Advisors: 0
Mr. Edelman: 0
Master Fund: 0
(iv) Shared power to dispose or to direct the disposition of:
Perceptive Advisors: 6,889,163
Mr. Edelman: 6,889,163
Master Fund: 6,889,163
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
Not Applicable
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
What stake does Perceptive Advisors report in XFOR?
Perceptive Advisors reports beneficial ownership of 6,889,163 shares, equal to 7.3% of common stock based on 94,319,696 shares outstanding as of May 1, 2026. The filing shows shared voting and dispositive power.
How many shares and warrants does the Master Fund hold in XFOR?
The Master Fund directly holds 6,737,648 shares and 151,515 Warrants immediately exercisable for common stock, subject to a beneficial ownership cap that limits aggregate holdings to 9.99%.
What is the Beneficial Ownership Limitation noted in the filing?
The filing states a Beneficial Ownership Limitation that prevents warrant exercise if post‑exercise ownership would exceed 9.99% of outstanding common stock; the limitation currently permits exercise for 151,515 shares.
Who controls the reported holdings for the Perceptive group?
Perceptive Advisors serves as investment manager to the Master Fund and Joseph Edelman is the managing member; the filing attributes shared voting and shared dispositive power to these reporting persons over the disclosed shares.
Are the reported ownership percentages based on a specific date?
Yes, the ownership percentages are calculated using 94,319,696 shares outstanding as of May 1, 2026, as cited from the issuer's Form 10‑Q referenced in the filing.
