[Form 4] Tandem Diabetes Care, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Leigh A. Vosseller, EVP & Chief Financial Officer of Tandem Diabetes Care, Inc. (TNDM), reported multiple transactions on 08/15/2025 related to vested restricted stock units (RSUs) and tax-withholding events. The filing shows two RSU vesting events that resulted in the acquisition of 1,503 and 1,495 shares each (total 2,998 shares) at $0 price upon vesting, increasing her direct holdings. The report also records share withholdings to satisfy tax obligations: 538 and 535 shares withheld at $10.82 per share. Following the transactions, total directly held common stock positions reported are 4,509 and 10,469 shares tied to two RSU awards, and 35,723–36,258 shares in various lines; additionally, 25,580 shares are held indirectly in the Leigh A. Vosseller Trust. The form was signed by an attorney-in-fact on 08/19/2025.

Insights

Securities Analyst

TL;DR: Insider received vested RSUs (2,998 shares) with partial withholding for taxes; overall holdings remain substantial and changes are routine.

The transactions are standard compensation-related events: two RSU vestings produced 1,503 and 1,495 shares issued on 08/15/2025, with the company withholding 538 and 535 shares to meet tax obligations at an indicated price of $10.82 per withheld share. No open-market sales occurred. The reporting shows both direct holdings from vested awards and indirect holdings via a trust (25,580 shares). These actions reflect compensation mechanics rather than discretionary liquidity events and are unlikely to be materially market-moving on their own.

Corporate Governance Expert

TL;DR: Filing reflects compliant disclosure of insider compensation vesting and tax withholding; governance procedures appear followed.

The Form 4 documents RSU awards from the 2023 Long-Term Incentive Plan (awarded May 2023 and May 2024) vesting according to schedule and the company’s withholding to satisfy tax liabilities. The filing includes the trustee-held shares disclosure and is signed by an attorney-in-fact, indicating timely compliance with Section 16 reporting. There are no indications of open-market share sales or other atypical insider actions in this submission.

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

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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^*

Vosseller Leigh

(Last) (First) (Middle)

12400 HIGH BLUFF DRIVE

(Street)

SAN DIEGO CA 92130

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
TANDEM DIABETES CARE INC [ TNDM ]

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

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	EVP & CHIEF FINANCIAL OFFICER

3. Date of Earliest Transaction (Month/Day/Year)
08/15/2025

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

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

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

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)
			Code	V	Amount	(A) or (D)	Price
Common Stock	08/15/2025		M		1,503	A	$0	35,301	D
Common Stock	08/15/2025		F(1)		538	D	$10.82	34,763	D
Common Stock	08/15/2025		M		1,495	A	$0	36,258	D
Common Stock	08/15/2025		F(1)		535	D	$10.82	35,723	D
Common Stock								25,580	I	Leigh A. Vosseller Trust(2)

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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Restricted Stock Unit(3)	(4)	08/15/2025		M			1,503	(5)	(5)	Common Stock	1,503	$0	4,509	D
Restricted Stock Unit(6)	(4)	08/15/2025		M			1,495	(7)	(7)	Common Stock	1,495	$0	10,469	D

Explanation of Responses:

1. Shares withheld by Tandem Diabetes Care, Inc. (the Company) to satisfy tax withholding requirements on vesting of restricted stock units (RSU). No shares were sold.

2. The securities are held by the Leigh A. Vosseller Trust dated January 17, 2010, of which Leigh Vosseller is the Trustee.

3. Awarded on May 25, 2023 pursuant to the Tandem Diabetes Care, Inc. 2023 Long-Term Incentive Plan, as amended, and agreements related thereto (the 2023 Plan).

4. Each RSU represents a contingent right to receive either one share of common stock of the Issuer or cash in lieu thereof, at the Issuer's discretion, in accordance with the terms of the 2023 Plan.

5. RSU vest as to thirty-three percent (33%) of the total number of shares subject to the RSU on 5/15/2024, and the remaining shares shall vest in eight (8) equal quarterly installments thereafter.

6. Awarded on May 23, 2024 pursuant to the 2023 Plan.

7. RSU vest as to thirty-three percent (33%) of the total number of shares subject to the RSU on 5/15/2025, and the remaining shares shall vest in eight (8) equal quarterly installments thereafter.

Remarks:

	/s/ Rachel Malina, Attorney-in-Fact for Leigh A. Vosseller	08/19/2025
	** 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.

FAQ

What transactions did Leigh A. Vosseller report on Form 4 for TNDM?

Answer: RSU vesting on 08/15/2025 resulting in acquisitions of 1,503 and 1,495 shares, and withholding of 538 and 535 shares for taxes.

How many vested RSU shares did the CFO receive on 08/15/2025?

Answer: A total of 2,998 vested shares (1,503 + 1,495) were reported as acquired upon vesting.

Were any shares sold in these transactions?

Answer: No shares were sold; shares were withheld by the company solely to satisfy tax withholding requirements.

What indirect holdings does the filing disclose for Leigh A. Vosseller?

Answer: The filing discloses 25,580 shares held indirectly in the Leigh A. Vosseller Trust dated January 17, 2010.

What withholding price is shown for the tax-withheld shares?

Answer: The withheld shares are recorded at a price of $10.82 per share.