Capital World Investors holds 12.8% of Ionis (NASDAQ: IONS)

Rhea-AI Filing Summary

Capital World Investors filed an amended Schedule 13G/A reporting beneficial ownership of 21,186,369 shares of Ionis Pharmaceuticals common stock, representing 12.8% of the 165,192,011 shares outstanding as of 03/31/2026. The filing states CWI has sole voting and dispositive power over these shares. The amendment is signed by a CRMC officer on 05/13/2026.

Insights

Institutional Ownership Analyst

Large passive stake disclosed: 21,186,369 shares (12.8%).

The filing shows Capital World Investors is the beneficial owner of 21,186,369 shares, with sole voting and dispositive authority, and states the stake equals 12.8% of 165,192,011 shares outstanding as of 03/31/2026.

The position size indicates a meaningful institutional holding without further action described; future filings may disclose any changes in voting or disposition. Cash‑flow treatment or trading intent is not stated in the excerpt.

Key Figures

Beneficially owned shares: 21,186,369 shares Percent of class: 12.8% Shares outstanding (basis): 165,192,011 shares +1 more

4 metrics

Beneficially owned shares 21,186,369 shares reported by Capital World Investors

Percent of class 12.8% of 165,192,011 shares outstanding

Shares outstanding (basis) 165,192,011 shares as of <date>03/31/2026</date>

Filing signature date 05/13/2026 amendment signed by CRMC officer

Key Terms

Schedule 13G/A, beneficial owner, sole dispositive power, shares outstanding

4 terms

Schedule 13G/A regulatory

"Amendment No. 2 ) Ionis Pharmaceuticals, Inc."

A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.

beneficial owner financial

"CWI is deemed to be the beneficial owner of 21,186,369 shares"

A beneficial owner is the person who ultimately owns or controls a financial asset or property, even if their name isn't directly on official documents. Think of it like someone who secretly holds the keys to a safe deposit box—others may appear to have access, but the true owner is the one who benefits from what's inside. Identifying beneficial owners helps ensure transparency and prevent illegal activities like money laundering or fraud.

sole dispositive power regulatory

"Sole power to dispose or to direct the disposition of: 21,186,369"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

shares outstanding market

"165,192,011 shares believed to be outstanding"

Shares outstanding are the total number of a company’s stock units held by all shareholders, including institutional investors and company insiders — think of them as the total number of slices of the company’s ownership pie. Investors use this number to calculate how much of the company each share represents, and it directly affects per-share measures like earnings per share, ownership percentage and valuation; when the slice count changes, an investor’s claim and the company’s per-share metrics change too.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 2)

Ionis Pharmaceuticals, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

462222100

(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): 462222100

1

Names of Reporting Persons

Capital World Investors

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 21,186,369.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 21,186,369.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

21,186,369.00

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)

12.8 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Ionis Pharmaceuticals, Inc.
(b)	Address of issuer's principal executive offices: 2855 GAZELLE COURT, CARLSBAD, CA 92010
Item 2.
(a)	Name of person filing: Capital World Investors
(b)	Address or principal business office or, if none, residence: 333 SOUTH HOPE STREET, 55TH FLOOR, LOS ANGELES, CALIFORNIA 90071
(c)	Citizenship: N/A
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: 462222100
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: 21,186,369 ** **Capital World Investors ("CWI") is a division of Capital Research and Management Company ("CRMC"), as well as its investment management subsidiaries and affiliates Capital Bank and Trust Company, Capital International, Inc., Capital International Limited, Capital International Sarl, Capital International K.K., Capital Group Private Client Services, Inc., and Capital Group Investment Management Private Limited (together with CRMC, the "investment management entities"). CWI's divisions of each of the investment management entities collectively provide investment management services under the name "Capital World Investors." CWI is deemed to be the beneficial owner of 21,186,369 shares or 12.8% of the 165,192,011 shares believed to be outstanding.
(b)	Percent of class: 12.8 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 21,186,369
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 21,186,369
	(iv) Shared power to dispose or to direct the disposition of: 0
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 acquired and are held in the ordinary course of business and 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.

Capital World Investors

Signature:	Jae Won Chung
Name/Title:	Senior Vice President and Associate General Counsel, Capital Research and Management Company
Date:	05/13/2026

FAQ

What stake does Capital World Investors report in Ionis (IONS)?

Capital World Investors reports beneficial ownership of 21,186,369 shares, equal to 12.8% of the company’s common stock based on 03/31/2026 outstanding shares of 165,192,011.

Does the filing state who controls voting and disposition of the Ionis shares?

Yes. The filing states CWI has sole voting power and sole dispositive power over all 21,186,369 shares, meaning it can direct votes and sales for those shares.

What form was filed to report this ownership in Ionis (IONS)?

An amended Schedule 13G/A was filed, which is used by certain institutional investors to report beneficial ownership when passive or meeting applicable requirements; the amendment is signed on 05/13/2026.

Is the 12.8% stake calculated against a specific shares outstanding figure?

Yes. The filing states the 12.8% figure is based on 165,192,011 shares believed to be outstanding as of the date referenced in the filing excerpt.

Does the filing describe any planned sales or purchases by Capital World Investors?

No. The amendment discloses beneficial ownership and voting/dispositive power but does not state any planned purchases, sales, or intent to transact in the provided excerpt.