Was the INSM insider sale by William Lewis a discretionary trade or tax related?

The Form 4 footnote states the 13,283 INSM shares sold by William Lewis were to satisfy tax withholding obligations upon vesting of Restricted Stock Units and to cover broker fees. This characterizes the sale as tax-related rather than a purely discretionary market transaction.

What does the Form 4 footnote reveal about William Lewis’s INSM share sale?

The footnote explains that the shares were sold to satisfy tax withholding obligations triggered by vesting Restricted Stock Units and to pay related broker fees. This context indicates the transaction is part of standard equity compensation mechanics, not a standalone strategic sale.

INSMED (INSM) CEO Lewis sells 13,283 shares to cover RSU tax obligations

Filing Impact

(Very High)

Filing Sentiment

(Negative)

Form Type

Rhea-AI Filing Summary

INSMED Inc Chair and CEO William Lewis reported an insider transaction involving company Common Stock. On May 13, 2026, he sold 13,283 shares at $116.18 per share, with a footnote explaining the shares were sold to satisfy tax withholding obligations upon the vesting of Restricted Stock Units and related broker fees.

Following this sale, Lewis held 287,902 shares of Common Stock directly and 233,924 shares indirectly through a trust, indicating he retains a substantial equity stake in INSMED after these tax-related transactions.

Insider Trade Summary

Net Seller: 13,283 shares ($1,543,219)

Net Sell 2 txns

Insider Lewis William

Role Chair and CEO

Sold 13,283 shs ($1.54M)

Type	Security	Shares	Price	Value
Sale	Common Stock	13,283	$116.18	$1.54M
holding	Common Stock	--	--	--

Holdings After Transaction: Common Stock — 287,902 shares (Direct, null); Common Stock — 233,924 shares (Indirect, By trust)

Footnotes (1)

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Key Figures

Shares sold: 13,283 shares Sale price: $116.18 per share Direct holdings after transaction: 287,902 shares +1 more

4 metrics

Shares sold 13,283 shares Common Stock sold on May 13, 2026

Sale price $116.18 per share Price for 13,283 Common Stock shares

Direct holdings after transaction 287,902 shares Common Stock held directly by William Lewis after sale

Indirect holdings after transaction 233,924 shares Common Stock held indirectly by trust

Key Terms

Restricted Stock Units, tax withholding obligations, Common Stock, open-market sale

4 terms

Restricted Stock Units financial

"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.

tax withholding obligations financial

"Shares sold to satisfy tax withholding obligations upon the vesting of Restricted Stock Units"

Common Stock financial

"INSMED Inc Common Stock on May 13, 2026"

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.

open-market sale financial

"transaction_action is described as an open-market sale of Common Stock"

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.

Form 4 Insider Transactions: What Each Field Means →

05/15/2026 - 04:06 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^*

Lewis William

(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)

X	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	Chair and CEO

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⁾		13,283	D	$116.18	287,902	D
Common Stock								233,924	I	By trust

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.

Remarks:

	/s/ William Lewis, 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 transaction did INSM (INSMED Inc) report for William Lewis?

INSMED Inc reported that Chair and CEO William Lewis sold 13,283 shares of Common Stock on May 13, 2026. The sale was tied to tax withholding obligations from vesting Restricted Stock Units and related broker fees, rather than a discretionary portfolio decision.

At what price were the INSM shares sold in William Lewis’s May 2026 transaction?

The reported sale by William Lewis was executed at $116.18 per share for 13,283 INSMED Inc Common Stock shares. This price reflects the transaction value used to satisfy tax withholding obligations associated with vesting Restricted Stock Units and to cover related broker fees.

How many INSMED Inc shares does William Lewis hold after this Form 4 filing?

After the reported transactions, William Lewis holds 287,902 INSMED Inc Common Stock shares directly. He also has 233,924 shares held indirectly through a trust, indicating continued significant exposure to the company’s equity following the tax-related share sale.