Insmed (NASDAQ: INSM) CMO sells 18,333 shares under Rule 10b5-1 plan

Q: Why did INSM’s CMO sell shares related to Restricted Stock Units?

A footnote explains that some shares were sold to satisfy tax withholding obligations upon the vesting of Restricted Stock Units and to cover related broker fees. This type of sale is a common administrative step when equity awards vest and taxes are due in shares.

Filing Impact

(Very High)

Filing Sentiment

(Negative)

Form Type

Rhea-AI Filing Summary

INSMED Inc Chief Medical Officer Martina Flammer sold 18,333 shares of common stock in open-market transactions. The sales occurred on May 13 and May 14, 2026 at prices around $112.76 to $117.54 per share. After these trades, she directly holds 64,910 shares. Footnotes explain that shares were sold to satisfy tax withholding obligations on vested Restricted Stock Units and that the transactions were executed under a pre-arranged Rule 10b5-1 trading plan.

Insider Trade Summary 10b5-1

Net Seller: 18,333 shares ($2,128,892)

Net Sell 3 txns

Insider Flammer Martina M.D.

Role Chief Medical Officer

Sold 18,333 shs ($2.13M)

Type	Security	Shares	Price	Value
Sale	Common Stock	10,479	$117.54	$1.23M
Sale	Common Stock	4,470	$112.76	$504K
Sale	Common Stock	3,384	$116.18	$393K

Holdings After Transaction: Common Stock — 64,910 shares (Direct, null)

Footnotes (1)

Shares sold to satisfy tax withholding obligations upon the vesting of Restricted Stock Units and to cover related broker fees. This is the weighted average sales price representing 4,470 shares sold at prices ranging from $112.65 to $112.85 per share. The Reporting Person undertakes to provide to the SEC staff, the issuer, or a security holder of the issuer the number of shares sold at each price within the price range upon request. This transaction was effected pursuant to a 10b5-1 trading plan adopted by the Reporting Person on February 27, 2025 in accordance with Rule 10b5-1 of the Securities Exchange Act of 1934, as amended.

Key Figures

Total shares sold: 18,333 shares Shares sold on May 14, 2026: 10,479 shares at $117.54 Shares sold on May 13, 2026 (trade 1): 3,384 shares at $116.18 +4 more

7 metrics

Total shares sold 18,333 shares Aggregate open-market sales in this Form 4

Shares sold on May 14, 2026 10,479 shares at $117.54 Open-market sale of common stock

Shares sold on May 13, 2026 (trade 1) 3,384 shares at $116.18 Open-market sale of common stock

Shares sold on May 13, 2026 (trade 2) 4,470 shares at ~$112.76 Weighted average price for this block

Shares held after transactions 64,910 shares Direct ownership following reported sales

Net buy/sell direction Net sale of 18,333 shares No offsetting purchases or exercises reported

10b5-1 plan adoption date February 27, 2025 Date CMO adopted trading plan

Key Terms

Restricted Stock Units, Rule 10b5-1 trading plan, open-market sale, tax withholding obligations

4 terms

Restricted Stock Units financial

"Shares sold to satisfy tax withholding obligations upon the vesting of Restricted Stock Units and to cover related broker fees."

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

Rule 10b5-1 trading plan regulatory

"This transaction was effected pursuant to a 10b5-1 trading plan adopted by the Reporting Person on February 27, 2025 in accordance with Rule 10b5-1."

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

open-market sale financial

"Sale in open market or private transaction"

An open-market sale is when a shareholder sells existing shares directly on a public exchange to any willing buyer, rather than through a private deal. Think of it like putting goods on a busy market stall where price is set by supply and demand; for investors it matters because such sales increase available supply, can put short-term downward pressure on the stock price, and signal changes in liquidity or investor confidence.

tax withholding obligations financial

"Shares sold to satisfy tax withholding obligations upon the vesting of Restricted Stock Units and to cover related broker fees."

Form 4 Insider Transactions: What Each Field Means →

05/15/2026 - 04:07 PM

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Flammer Martina M.D.

(Last)

(First)

(Middle)

700 US HIGHWAY 202/206

(Street)

BRIDGEWATER

NEW JERSEY

08807

(City)

(State)

(Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
INSMED Inc [ INSM ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	Chief Medical Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
05/13/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	05/13/2026		S⁽¹⁾		4,470	D	$112.76⁽²⁾	78,773	D
Common Stock	05/13/2026		S⁽¹⁾		3,384	D	$116.18	75,389	D
Common Stock	05/14/2026		S⁽³⁾		10,479	D	$117.54	64,910	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)

Explanation of Responses:

1. Shares sold to satisfy tax withholding obligations upon the vesting of Restricted Stock Units and to cover related broker fees.

2. This is the weighted average sales price representing 4,470 shares sold at prices ranging from $112.65 to $112.85 per share. The Reporting Person undertakes to provide to the SEC staff, the issuer, or a security holder of the issuer the number of shares sold at each price within the price range upon request.

3. This transaction was effected pursuant to a 10b5-1 trading plan adopted by the Reporting Person on February 27, 2025 in accordance with Rule 10b5-1 of the Securities Exchange Act of 1934, as amended.

Remarks:

	/s/ Martina Flammer, M.D., by Michael A. Smith as Attorney-in-fact	05/15/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)

Source: View Original Filing on SEC EDGAR

FAQ

What insider activity did INSM (INSM) report for Martina Flammer?

INSMED Inc reported that Chief Medical Officer Martina Flammer sold 18,333 shares of common stock in open-market transactions. The trades occurred over two days and were partly linked to tax withholding obligations on vested Restricted Stock Units and executed under a Rule 10b5-1 trading plan.

How many INSM shares did the CMO sell and at what prices?

Martina Flammer sold 18,333 INSMED common shares. The transactions included 4,470 shares at a weighted average of about $112.76 and additional blocks at $116.18 and $117.54 per share, reflecting typical open-market pricing across the two reported trading days.

How many INSM shares does the CMO hold after these sales?

After the reported sales, Chief Medical Officer Martina Flammer directly holds 64,910 INSMED common shares. This figure comes from the post-transaction ownership reported in the Form 4, giving investors a snapshot of her remaining direct equity position in the company.

Were the recent INSM insider sales part of a 10b5-1 plan?

Yes. A footnote states the transactions were effected under a Rule 10b5-1 trading plan adopted on February 27, 2025. Such plans pre-schedule trades, indicating the timing of these sales was determined in advance rather than based on short-term market developments.

What does the Form 4 reveal about INSM insider trading direction?

The Form 4 shows net selling activity by INSMED’s Chief Medical Officer, with three open-market sale transactions totaling 18,333 shares. No purchases, option exercises, gifts, or other acquisition transactions are reported in this filing, indicating a purely net-sell profile for the covered period.