Cytek Biosciences: Boston Partners reports 6.16% stake

Available on EDGAR 11/13/2026 - 11:47 AM EST Accepted by SEC EDGAR 11/13/2026 - 11:47 AM EST Learn about SEC filing dates

Rhea-AI Filing Summary

Cytek Biosciences, Inc. (CTKB) is the issuer in an amended ownership disclosure in which Boston Partners reported beneficial ownership of 8,002,638 common shares, equal to 6.16% of the class, as of September 30, 2026. The shares were held for discretionary accounts of certain clients. Boston Partners reported sole voting power over 6,503,524 shares and sole dispositive power over 8,002,638 shares, with no shared voting or dispositive power.

Key Figures

Beneficial ownership: 8,002,638 shares Percent of class: 6.16% Sole voting power: 6,503,524 shares +1 more

4 metrics

Beneficial ownership 8,002,638 shares Boston Partners reported this amount as of September 30, 2026

Percent of class 6.16% Boston Partners' reported beneficial ownership as of September 30, 2026

Sole voting power 6,503,524 shares Boston Partners' reported voting power

Sole dispositive power 8,002,638 shares Boston Partners' reported dispositive power

Key Terms

beneficial owner, Rule 13d-3, sole voting power, sole dispositive power

4 terms

beneficial owner regulatory

"may be deemed to be a beneficial owner"

A beneficial owner is the person who ultimately owns or controls a financial asset or property, even if their name isn't directly on official documents. Think of it like someone who secretly holds the keys to a safe deposit box—others may appear to have access, but the true owner is the one who benefits from what's inside. Identifying beneficial owners helps ensure transparency and prevent illegal activities like money laundering or fraud.

Rule 13d-3 regulatory

"By reason of rule 13d-3"

Rule 13d-3 defines who is treated as the beneficial owner of a company’s shares for U.S. securities disclosure rules — essentially anyone who has the power to vote or direct how shares are voted, or the power to buy or sell them, even if they don’t hold the certificates. For investors this matters because crossing certain ownership thresholds triggers public filing and disclosure obligations and signals potential control or influence, much like having the keys to a car implies you can drive it even if it’s registered to someone else.

sole voting power regulatory

"Sole power to vote or to direct the vote"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

sole dispositive power regulatory

"Sole power to dispose or to direct the disposition"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

FAQ

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

How many CTKB shares did Boston Partners report owning?

Boston Partners reported beneficial ownership of 8,002,638 Cytek Biosciences common shares, or 6.16% of the class, as of September 30, 2026. It held the shares for discretionary accounts of certain clients.

Why does Boston Partners report beneficial ownership of CTKB shares?

Boston Partners stated that it may be deemed a beneficial owner under Rule 13d-3 of shares held for discretionary accounts of certain clients.

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

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Cytek Biosciences, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

23285D109

(CUSIP Number)

09/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 23285D109

1

Names of Reporting Persons

Boston Partners

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 6,503,524.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 8,002,638.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

8,002,638.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

6.16 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Cytek Biosciences, Inc.
(b)	Address of issuer's principal executive offices: 47215 LAKEVIEW BOULEVARD, FREMONT, CALIFORNIA 94538
Item 2.
(a)	Name of person filing: Boston Partners
(b)	Address or principal business office or, if none, residence: ONE BEACON STREET 30TH FLOOR BOSTON, Massachusetts 02108
(c)	Citizenship: Boston Partners - DELAWARE
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: 23285D109
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: 8,002,638
(b)	Percent of class: 6.16 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: Boston Partners - 6,503,524
	(ii) Shared power to vote or to direct the vote: Boston Partners - 0
	(iii) Sole power to dispose or to direct the disposition of: Boston Partners - 8,002,638
	(iv) Shared power to dispose or to direct the disposition of: Boston Partners - 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. This Schedule is being filed with respect to 8,002,638 shares of Cytek Biosciences, Inc. (the Common Stock) held by Boston Partners on 09/30/2026 for the discretionary account of certain clients. By reason of rule 13d-3 under the act Boston Partners may be deemed to be a beneficial owner of such Common Stock. To the knowledge of Boston Partners no person has the right to receive or the power to direct the receipt of dividends from or the proceeds from the sale of such Common Stock which represents more than 5% of the outstanding shares of the Common Stock referred to in item 4(b) hereof.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Boston Partners

Signature:	/s/ Ali Farooqi
Name/Title:	Ali Farooqi / Senior Compliance Manager
Date:	11/13/2026