Notice of Proposed Sale · 144

MKS Inc.

MKSINASDAQEQUITYCurrent

Notice of Proposed Sale

Filed Aug 3, 2026Accepted Aug 3, 2026, 12:47 PM EDTFiling CIK 1710173Accession 0001959173-26-005513

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Structured filing — 144

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Notice of proposed sale. The proposed amounts below do not establish that a sale occurred.

Proposed-sale notice

Issuer: MKS INC
Issuer CIK: 0001049502
SEC file number: 000-23621
Phone: 978-645-5500
Person for whose account securities are to be sold: Williams John Edward
Relationships to issuer: Officer
Street: 2 TECH DRIVE
City: ANDOVER
State / country code: MA
Postal code: 01810

Securities proposed for sale

Securities proposed for sale · 1 reported row
Security	Proposed units	Aggregate market value	Units outstanding	Approximate sale date	Exchange	Broker / market maker
Common	457	131,757.67	67,544,129	08/03/2026	NASDAQ	Fidelity Brokerage Services LLC

Broker / market maker — proposed row 1, entry 1

Name: Fidelity Brokerage Services LLC
Street: 900 Salem Street
City: Smithfield
State / country code: RI
Postal code: 02917

Acquisition of securities to be sold

Acquisition of securities to be sold · 1 reported row
Security	Acquired	Nature of acquisition	Acquired from	Amount acquired	Gift transaction	Payment date	Nature of payment
Common	04/17/2026	Restricted Stock Vesting	Issuer	457	N	04/17/2026	Compensation

Prior-sale reporting

Nothing to report for the preceding three months: Y

Notice signature

Notice date: 08/03/2026
Signed: /s/ Daniel Tucci, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for John Williams
Plan adoption dates: 03/05/2026

Company context

MKS Inc. (NASDAQ: MKSI) enables technologies that transform our world. We deliver foundational technology solutions to leading edge semiconductor manufacturing, electronics and packaging, and specialty industrial applications. We apply our broad science and engineering capabilities to create instruments, subsystems, systems, process control solutions and specialty chemicals technology that improve process performance, optimize productivity and enable unique innovations for many of the world's leading technology and industrial companies. Our solutions are critical to addressing the challenges of miniaturization and complexity in advanced device manufacturing by enabling increased power, speed, feature enhancement, and optimized connectivity. Our solutions are also critical to addressing ever-increasing performance requirements across a wide array of specialty industrial applications. Additional information can be found at www.mks.com.

Current securities

MKSINASDAQ · EQUITY · Current

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