Apple has released Safari Technology Preview 254, its experimental browser for web developers, with live pinch-to-zoom on macOS, new CSS sizing tools and HEVC video encoding for web apps. The WebKit team published the release notes on October 8, 2026, and the build is available for macOS Golden Gate and macOS Tahoe.
If you already run Safari Technology Preview, Apple says you can update it in System Settings under General, then Software Update. The release notes for Safari Technology Preview 254 list WebKit changes from 321068@main to 322634@main.
Live pinch-to-zoom on the Mac
The most visible change for anyone browsing is in rendering. WebKit says it “added live pinch-to-zoom on macOS, so content stays sharp during the gesture and fixed and sticky elements follow the zoom.” That means text should stay crisp mid-gesture, and headers or toolbars pinned to the page should scale with the rest of it.
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CSS: animate to auto, at last
For web designers, the headline additions are two long-requested CSS features:
- interpolate-size, which allows “animations and transitions to and from intrinsic sizing keywords such as auto, min-content, and fit-content”
- calc-size(), which allows “calculations on intrinsic sizes such as auto, fit-content, and max-content”
Together they address a common annoyance: smoothly expanding an accordion or menu to its natural height without measuring it in JavaScript first.
The release adds four more CSS features:
- The size, min-size and max-size shorthand properties
- Side shorthands for border radius, such as border-top-radius, which set both corners on one side of a box at once
- The symbols() function for anonymous counter styles
- CSS linked parameters, including the link-parameters property and param(), for passing values into linked SVG images
HEVC encoding and faster media for web apps
Two WebCodecs additions target video and audio web apps. WebCodecs can now produce HEVC video in Annex B format through a new hevc option in VideoEncoder configurations. A transfer option in several constructors, including VideoFrame, AudioData and ImageDecoder, lets “ownership of ArrayBuffer data to be transferred instead of copied.”
On the JavaScript side, Apple added WebAssembly wide arithmetic, with instructions for 128-bit integer addition and subtraction and for multiplying two 64-bit integers into a 128-bit result.
Fixes you might notice
Most of the release is bug fixes, more than 130 of them by our count of the notes, many in CSS Grid and line-clamp. A few touch everyday browsing:
- Paused media with audio in a hidden page could start playing again without a user gesture. That is fixed.
- On iOS, video could disappear while audio kept playing after moving from Picture in Picture to fullscreen and back.
- navigator.hardwareConcurrency returned unusual core counts to known fingerprinting scripts, which “could trigger bot detection challenges.” WebKit now alternates between 4 and 8 instead.
- VoiceOver could not press buttons, links and form controls styled with pointer-events: none, and announced every focused ARIA menu item as “selected.” Both are fixed.
- VoiceOver on iOS did not identify date, time and color inputs as pop-up buttons.
The notes also fix a Content Security Policy gap in workers, where violations did not fire securitypolicyviolation events.
What Safari Technology Preview is for
Apple describes Safari Technology Preview as “a standalone app that works side by side with the current version of Safari,” and says it “includes the most recent version of WebKit, the rendering engine that powers Safari.” Developers can send feedback through Feedback Assistant by choosing Report an Issue from the app’s Help menu.
Our last report in this series covered Safari Technology Preview 251. Releases 252 and 253 followed on September 11 and September 23, according to the WebKit blog, and version 254 is the first of October.
