FiledMay 29, 2026 - 6:44 PM ET

SIONORBIMED ADVISORS LLC ( Reporting ) CIK : 0001055951 (see all company filings)Nasdaq

OrbiMed Private Investments VIII, LP proposes to sell 1,082,480 shares

144Insider / OwnershipbearishImpact66

SION Price

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N/A$0.00 (+0.00%)

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Why It Matters

The proposed sale size is sizable versus outstanding shares and warrants follow-up if executed

Summary

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OrbiMed Private Investments VIII, LP filed a Form 144 proposing to sell 1,082,480 Sionna shares (aggregate value about $46.33M) with an approximate sale date of 05/29/2026. The proposed shares equal about 2.40% of shares outstanding (45,150,330). This follows prior scheduled sales totaling 858,981 shares in the past three months

Score66

Score Rationale

bearish

Proposed $46.3M sale, 2.40% of outstanding shares.

Bearish

Proposes 1,082,480 shares (~2.40% of outstanding)
Aggregate proposed value $46.33M
Prior three-month scheduled sales: 858,981 shares

Key Evidence

Form 144 filed by OrbiMed Private Investments VIII, LP
Proposed sale date 05/29/2026
Broker: TD Cowen

What To Watch Next

Subsequent Form 4 showing execution or cancellation
Amendment to Form 144 changing amount or date
Company or OrbiMed statements or SEC filings

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SION Market Context

Market Cap$1.85B

Shares Outstanding45.15M

Public Float26.34M

Public Float %58.3%

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Original Filing Text

SEC filing text preserved from the raw item store.

### 144
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
|

MASSACHUSETTS

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
|

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:

* 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)
|

### 144
144

0001055951
XXXXXXXX

LIVE

0002036042
Sionna Therapeutics, Inc.
001-42504

21 HICKORY DRIVE
SUITE 500
WALTHAM
MA
02451

617-819-2020
OrbiMed Private Investments VIII, LP

Shareholder

Common Stock

TD Cowen

599 Lexington Avenue
New York
NY
10022

1082480
46330144.00
45150330
05/29/2026
Nasdaq Stock Market

Common Stock
02/10/2025
IPO
Issuer
N
1082480
02/10/2025
Cash

OrbiMed Private Investments VIII, LP