SION Form 144: OrbiMed reports multiple share sales

SION submitted a Form 144 reporting proposed and completed sales of Common Stock by a selling holder.

Rhea-AI Filing Summary

SION submitted a Form 144 reporting proposed and completed sales of Common Stock by a selling holder. The filing lists multiple dispositions by OrbiMed Private Investments VIII, LP across 04/14/2026–05/27/2026, including lots of 235,863 shares on 04/15/2026 and 184,639 shares on 05/11/2026. The filing names the issuer, shows the securities class as Common Stock, and reports proceeds for each sale in dollars.

Insights

Securities Compliance Counsel

Form 144 lists multiple block dispositions by a single institutional holder over several dates.

The filing identifies OrbiMed Private Investments VIII, LP as the selling holder and records individual sales with share counts and dollar proceeds on specific dates, for example 04/15/2026 (235,863 shares, $10,528,924.32) and 05/11/2026 (184,639 shares, $8,534,014.58).

These entries are notifications under Rule 144 procedures. Cash flow recipients and any holding-period or legend-clearing qualifiers are shown only as the sale rows; additional conditions or issuer proceeds treatment are not stated in the excerpt.

Key Figures

Sale example: 235,863 shares Proceeds example: $10,528,924.32 Sale example: 184,639 shares +2 more

5 metrics

Sale example 235,863 shares sale on <date>04/15/2026</date>

Proceeds example <money>$10,528,924.32</money> proceeds from 235,863-share sale on <date>04/15/2026</date>

Sale example 184,639 shares sale on <date>05/11/2026</date>

Proceeds example <money>$8,534,014.58</money> proceeds from 184,639-share sale on <date>05/11/2026</date>

Sale example 22,6906 shares sale on <date>04/16/2026</date>

Key Terms

Form 144, Common Stock, selling holder

3 terms

Form 144 regulatory

"Form type listed as 144: Filer Information"

Form 144 is a document that investors must file with the government when they plan to sell a large number of shares of a company's stock. It helps ensure transparency so everyone knows how many shares are being sold and when, which can impact the stock's price.

Common Stock financial

"Securities Information shows Common Stock and IPO date"

Common stock represents ownership shares in a company, giving investors a stake in its success and a say in important decisions through voting rights. It is the most common type of stock traded on markets and can provide income through dividends, as well as potential for value growth. For investors, holding common stock means sharing in the company’s profits and risks.

selling holder financial

"OrbiMed Private Investments VIII, LP listed across dated sale rows"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What does SION's Form 144 disclose about recent sales?

It discloses multiple sales of Common Stock by OrbiMed Private Investments VIII, LP between 04/14/2026 and 05/27/2026. The filing lists share counts and gross proceeds for each dated disposition.

Who is the selling holder listed on the SION Form 144?

The selling holder is OrbiMed Private Investments VIII, LP, with an address shown as 601 Lexington Ave., New York. Multiple dated sales and corresponding proceeds are reported in the filing.

How large were the example sales reported for SION?

Examples include 235,863 shares on 04/15/2026 for $10,528,924.32 and 184,639 shares on 05/11/2026 for $8,534,014.58. Each row pairs shares with dollar proceeds.

Does the Form 144 show who received the sale proceeds for SION?

The excerpt pairs each disposition with a cash amount but does not state the ultimate recipient other than indicating the selling holder. The filing rows show gross proceeds for each dated sale.

Does SION's Form 144 state the securities class being sold?

Yes. The filing identifies the securities as Common Stock and notes an IPO origin date of 02/10/2025 in the securities table provided.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 05/29/2026 - 06:44 PM EDT Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001055951
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	Sionna Therapeutics, Inc.
SEC File Number	001-42504
Address of Issuer	21 HICKORY DRIVE SUITE 500 WALTHAM MASSACHUSETTS 02451
Phone	617-819-2020
Name of Person for Whose Account the Securities are To Be Sold	OrbiMed Private Investments VIII, LP
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Shareholder

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common Stock	TD Cowen 599 Lexington Avenue New York NY 10022	1082480	46330144.00	45150330	05/29/2026	Nasdaq Stock Market

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common Stock	02/10/2025	IPO	Issuer			1082480	02/10/2025	Cash

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	04/14/2026	47814	2128201.14
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	04/15/2026	235863	10528924.32
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	04/16/2026	226906	10287918.04
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	04/17/2026	52397	2341097.96
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	04/20/2026	2948	131244.96
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	05/07/2026	48546	2165637.06
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	05/08/2026	59767	2664412.86
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	05/11/2026	184639	8534014.58
OrbiMed Private Investments VIII, LP 601 Lexington Ave. 54th Floor New York NY 10022	Common Stock	05/27/2026	101	4493.49

144: Remarks and Signature

Remarks	OrbiMed Capital GP VIII LLC is the general partner of OrbiMed Private Investments VIII, LP. OrbiMed Advisors LLC is the managing member of OrbiMed Capital GP VIII LLC.
Date of Notice	05/29/2026
Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1	02/10/2025
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ Douglas Coon, Chief Compliance Officer, OrbiMed Advisors LLC, managing member of the general partner of OrbiMed Private Investments VIII, LP
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)