What do the RSU vesting schedules mean for Cytek (CTKB) CFO’s future share deliveries?

The footnotes describe RSU awards vesting over four years in fixed fractions on May 18, August 18, November 18, and March 10 each year. As tranches vest, additional common shares will be delivered, typically accompanied by tax-withholding share surrenders.

Cytek CFO exercises RSUs, uses shares for taxes

Cytek Biosciences Chief Financial Officer William D. McCombe reported routine equity compensation activity tied to Restricted Stock Units on May 18, 2026.

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Form Type

Rhea-AI Filing Summary

Cytek Biosciences Chief Financial Officer William D. McCombe reported routine equity compensation activity tied to Restricted Stock Units on May 18, 2026. He exercised RSU awards into 25,719 shares of common stock and had 9,229 shares withheld at $3.55 per share to cover tax obligations. Following these transactions, he directly holds 98,739 shares of common stock. The footnotes explain that each RSU represents a contingent right to one share and outline multi-year vesting schedules, indicating these events stem from scheduled vesting rather than open-market trades.

Insider Trade Summary

25,719 shares exercised/converted

Exercise 9 txns

Insider McCombe William D.

Role Chief Financial Officer

Type	Security	Shares	Price	Value
Exercise	Restricted Stock Units	6,320	$0.00	$0.00
Exercise	Restricted Stock Units	8,700	$0.00	$0.00
Exercise	Restricted Stock Units	10,699	$0.00	$0.00
Exercise	Common Stock	6,320	$0.00	$0.00
Exercise Price or Tax Liability	Common Stock	2,268	$3.55	$8K
Exercise	Common Stock	8,700	$0.00	$0.00
Exercise Price or Tax Liability	Common Stock	3,122	$3.55	$11K
Exercise	Common Stock	10,699	$0.00	$0.00
Exercise Price or Tax Liability	Common Stock	3,839	$3.55	$14K

Holdings After Transaction: Restricted Stock Units — 444,573 contracts (Direct); Common Stock — 111,177 shares (Direct)

Footnotes (5)

F1. Each Restricted Stock Unit (the "RSU Award") represents a contingent right to receive one share of the Issuer's common stock.
F2. Represents the number of shares withheld by and surrendered to the Issuer on May 18, 2026, to satisfy tax withholding obligations that arose in connection with the vesting of the RSU Award.
F3. The shares subject to the RSU Award shall vest over 4 years with 12/48 of the total shares underlying the RSU Award vesting on May 18, 2025; 3/48 of the total shares underlying the RSU Award vesting on August 18, 2025 and each August 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on November 18, 2025 and each November 18 thereafter; and 3/48 of the total shares underlying the RSU Award vesting on March 10, 2026 and each March 10 thereafter; and 3/48 of the total shares underlying the RSU Award vesting on May 18, 2026 and each May 18 thereafter.
F4. The shares subject to the RSU Award shall vest over 4 years with 2/48 of the total shares underlying the RSU Award vesting on May 18, 2025 and each May 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on August 18, 2025 and each August 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on November 18, 2025 and each November 18 thereafter; and 4/48 of the total shares underlying the RSU Award vesting on March 10, 2026 and each March 10 thereafter, until fully vested.
F5. The shares subject to the RSU Award shall vest over 4 years with 2/48 of the total shares underlying the RSU Award vesting on May 18, 2026 and each May 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on August 18, 2026 and each August 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on November 18, 2026 and each November 18 thereafter; and 4/48 of the total shares underlying the RSU Award vesting on March 10, 2027 and each March 10 thereafter, until fully vested.

Key Figures

RSU shares exercised: 25,719 shares Shares withheld for taxes: 9,229 shares Tax withholding price: $3.55 per share +2 more

5 metrics

RSU shares exercised 25,719 shares Total common shares from RSU exercises on May 18, 2026

Shares withheld for taxes 9,229 shares Tax-withholding dispositions on May 18, 2026

Tax withholding price $3.55 per share Value used for tax-withholding share surrenders

Shares held after transactions 98,739 shares Direct common stock holdings following May 18, 2026 activity

RSU balance (award 1) 246,091 units Restricted Stock Units remaining after May 18, 2026 for one award

Key Terms

Restricted Stock Unit, RSU Award, tax withholding obligations, vest, +1 more

5 terms

Restricted Stock Unit financial

"Each Restricted Stock Unit (the "RSU Award") represents a contingent right to receive one share"

A restricted stock unit is a promise from a company to give an employee shares of stock after certain conditions are met, like staying with the company for a set amount of time. It’s like earning a bonus that turns into company stock once you’ve proven your commitment, making it a way to motivate and reward employees.

RSU Award financial

"Each Restricted Stock Unit (the "RSU Award") represents a contingent right to receive one share"

tax withholding obligations financial

"shares withheld by and surrendered to the Issuer ... to satisfy tax withholding obligations"

vest financial

"The shares subject to the RSU Award shall vest over 4 years with 12/48 of the total shares"

A vest is the process by which an employee earns the right to receive certain benefits or ownership interests, such as stock or retirement funds, over time. It’s similar to earning a reward gradually, ensuring that the benefit becomes fully yours only after a set period or meeting specific conditions. This makes it important for investors because it determines when they can actually claim or use those benefits.

contingent right financial

"represents a contingent right to receive one share of the Issuer's common stock"

FAQ

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

What insider transactions did Cytek (CTKB) CFO William D. McCombe report?

Cytek CFO William D. McCombe reported RSU-related activity on May 18, 2026. He exercised awards into 25,719 common shares and had 9,229 shares withheld to satisfy tax obligations, with no open-market purchases or sales disclosed.

How many Cytek (CTKB) shares does the CFO hold after these Form 4 transactions?

After the reported transactions, Cytek CFO William D. McCombe directly holds 98,739 shares of common stock. This figure reflects RSU vesting and related tax withholding, rather than discretionary buying or selling in the open market.

Were Cytek (CTKB) CFO transactions open-market buys or sales?

The reported transactions were not open-market buys or sales. They reflect RSU exercises (code M) and tax-withholding dispositions (code F), where shares are surrendered to cover tax liabilities triggered by vesting, rather than traded with outside investors.

What RSU activity did the Cytek (CTKB) Form 4 disclose for the CFO?

The Form 4 shows McCombe exercised Restricted Stock Units into 25,719 common shares at a stated conversion price of $0.00. Each RSU represents a contingent right to one share, and the vesting follows multi-year schedules described in the footnotes.

How many Cytek (CTKB) shares were used to cover the CFO’s tax obligations?

A total of 9,229 Cytek common shares were withheld and surrendered to the issuer at $3.55 per share. These tax-withholding dispositions (code F) occurred in three tranches tied to RSU vesting on May 18, 2026.

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

Form 4 Insider Transactions: What Each Field Means →

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Accepted by SEC EDGAR 05/20/2026 - 05:48 PM EDT

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^*

McCombe William D.

(Last)

(First)

(Middle)

C/O CYTEK BIOSCIENCES, INC.

47215 LAKEVIEW BOULEVARD

(Street)

FREMONT

CALIFORNIA

94538

(City)

(State)

(Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Cytek Biosciences, Inc. [ CTKB ]

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
05/18/2026

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	05/18/2026		M		6,320	A	⁽¹⁾	101,007	D
Common Stock	05/18/2026		F		2,268⁽²⁾	D	$3.55	98,739	D
Common Stock	05/18/2026		M		8,700	A	⁽¹⁾	107,439	D
Common Stock	05/18/2026		F		3,122⁽²⁾	D	$3.55	104,317	D
Common Stock	05/18/2026		M		10,699	A	⁽¹⁾	115,016	D
Common Stock	05/18/2026		F		3,839⁽²⁾	D	$3.55	111,177	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)
Restricted Stock Units	⁽¹⁾	05/18/2026		M			6,320	⁽³⁾	⁽³⁾	Common Stock	6,320	$0	50,569	D
Restricted Stock Units	⁽¹⁾	05/18/2026		M			8,700	⁽⁴⁾	⁽⁴⁾	Common Stock	8,700	$0	147,913	D
Restricted Stock Units	⁽¹⁾	05/18/2026		M			10,699	⁽⁵⁾	⁽⁵⁾	Common Stock	10,699	$0	246,091	D

Explanation of Responses:

1. Each Restricted Stock Unit (the "RSU Award") represents a contingent right to receive one share of the Issuer's common stock.

2. Represents the number of shares withheld by and surrendered to the Issuer on May 18, 2026, to satisfy tax withholding obligations that arose in connection with the vesting of the RSU Award.

3. The shares subject to the RSU Award shall vest over 4 years with 12/48 of the total shares underlying the RSU Award vesting on May 18, 2025; 3/48 of the total shares underlying the RSU Award vesting on August 18, 2025 and each August 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on November 18, 2025 and each November 18 thereafter; and 3/48 of the total shares underlying the RSU Award vesting on March 10, 2026 and each March 10 thereafter; and 3/48 of the total shares underlying the RSU Award vesting on May 18, 2026 and each May 18 thereafter.

4. The shares subject to the RSU Award shall vest over 4 years with 2/48 of the total shares underlying the RSU Award vesting on May 18, 2025 and each May 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on August 18, 2025 and each August 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on November 18, 2025 and each November 18 thereafter; and 4/48 of the total shares underlying the RSU Award vesting on March 10, 2026 and each March 10 thereafter, until fully vested.

5. The shares subject to the RSU Award shall vest over 4 years with 2/48 of the total shares underlying the RSU Award vesting on May 18, 2026 and each May 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on August 18, 2026 and each August 18 thereafter; 3/48 of the total shares underlying the RSU Award vesting on November 18, 2026 and each November 18 thereafter; and 4/48 of the total shares underlying the RSU Award vesting on March 10, 2027 and each March 10 thereafter, until fully vested.

	/s/ Valerie Barnett, Attorney-in-Fact	05/20/2026
	** 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