[Form 3] CABOT CORP Initial Statement of Beneficial Ownership

Rhea-AI Filing Summary

Cabot Corporation reported the equity holdings of Senior Vice President William F. Masterson III in a beneficial ownership statement. He directly owns 3,724 shares of Cabot common stock, which include 942 performance-based units earned on Cabot's performance in fiscal years 2024 and 2025 that remain subject to time-based vesting, and 1,801 units that are subject to time-based vesting only. He also holds 289.9275 shares of phantom stock, each economically equivalent to one Cabot common share, which will be settled in Cabot common stock when his employment with the company ends.

SEC Form 3

FORM 3

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

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

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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1. Name and Address of Reporting Person^*

Masterson William F III

(Last) (First) (Middle)

C/O CABOT CORPORATION

TWO SEAPORT LANE, SUITE 1400

(Street)

BOSTON MA 02210

(City) (State) (Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
11/21/2025

3. Issuer Name and Ticker or Trading Symbol
CABOT CORP [ CBT ]

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

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Senior Vice President

5. 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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	3,724(1)	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Phantom Stock	(2)	(2)	Common Stock	289.9275	$0	D

Explanation of Responses:

1. Includes 942 performance based units earned on the basis of the Corporation's performance in fiscal years 2024 and 2025 (which remain subject to time-based vesting) and 1,801 units subject to time-based vesting.

2. Each share of phantom stock is the economic equivalent of one share of Cabot Corporation common stock. The shares of phantom stock will be settled in shares of Cabot Corporation common stock upon termination of his employment with Cabot Corporation.

Remarks:

Exhibit-24 Power of Attorney attached.

	By: Jennifer Lombardi, pursuant to a power of attorney from William F. Masterson, III	12/02/2025
	** 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 5 (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.
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FAQ

What insider ownership does CBT executive William F. Masterson III report?

Senior Vice President William F. Masterson III reports direct ownership of 3,724 shares of Cabot Corporation common stock, plus 289.9275 shares of phantom stock tied to Cabot common shares.

How many Cabot (CBT) performance-based units does the executive hold?

The executive’s total 3,724 common stock units include 942 performance-based units earned based on Cabot’s performance in fiscal years 2024 and 2025, which remain subject to time-based vesting.

What time-based vesting units are reported by the CBT executive?

Within the reported 3,724 common stock units, 1,801 units are subject to time-based vesting, meaning they vest over time according to Cabot’s equity plan terms.

What is the nature of Cabot (CBT) phantom stock held by the executive?

The executive holds 289.9275 shares of phantom stock. Each phantom share is the economic equivalent of one Cabot common share and will be settled in Cabot common stock upon termination of his employment.

Is the reported Cabot (CBT) stock ownership held directly or indirectly?

Both the 3,724 shares of Cabot common stock and the 289.9275 phantom stock shares are reported as held in direct ownership form by the executive.

What is William F. Masterson III’s role at Cabot Corporation?

William F. Masterson III is reported as an officer of Cabot Corporation with the title Senior Vice President, and the filing reflects his beneficial ownership in that capacity.