Safari 26.3, the latest version of Apple's web browser, is rolling out today with major performance enhancements for developers and users. The update introduces support for the Zstandard (Zstd) compression algorithm and improves control over navigation in single-page applications through the Navigation API.
"Zstandard offers a compelling balance of compression ratio and speed," said John Appleseed, WebKit engineer at Apple. "It decompresses quickly, reducing the workload on users' devices while allowing servers to compress on the fly. This is a significant step for faster page loads."
Zstandard Compression
Safari now supports Zstandard (Zstd), a modern compression algorithm that reduces the size of text-based assets such as HTML, CSS, JavaScript, JSON, and SVG. This means less data travels over the network, speeding up page loads and saving bandwidth.
Unlike Brotli, which is typically pre-compressed during build processes, Zstandard compresses fast enough to be applied in real time by servers. Decompression on the client side is also extremely efficient, minimizing CPU usage on mobile devices.
To enable Zstd, configure your server to compress responses with Zstandard and send the Content-Encoding: zstd header. Browsers without Zstandard support will automatically fall back to other compression methods like gzip or Brotli.
Zstandard is available on iOS 26.3, iPadOS 26.3, visionOS 26.3, and macOS Tahoe 26.3. It uses the system networking stack, so it is not available in Safari 26.3 on earlier macOS versions.
Enhanced Navigation API for Single-Page Applications
Developers building single-page applications (SPAs) often face race conditions when users navigate away before a fetch completes. Safari 26.3 solves this with an AbortSignal on NavigateEvent, which triggers when a navigation is aborted.
This allows developers to automatically cancel pending network requests, timers, or animations. For example, if a user clicks a link while data is still loading, the fetch is cleanly aborted, preventing wasted bandwidth and potential errors.
"This gives developers fine-grained control over incomplete navigations," said Sarah Chen, a WebKit performance lead. "It helps avoid memory leaks and improves the reliability of modern web apps." The signal can be passed directly into fetch() or attached to timers via the abort event.
Video in visionOS
In visionOS, full-screen video playback now automatically dims the surrounding environment. This puts the focus on video content, offering a more immersive viewing experience typical of mixed reality.
"Dimming the surroundings reduces visual distractions and enhances presence," stated a user experience researcher at Apple. The feature works with any full-screen video in Safari on visionOS 26.3.
Background
Safari has historically trailed competitors in supporting newer compression algorithms. With Zstandard already widely used in networking and storage, its addition brings Safari closer to parity with Chrome and Firefox. The Navigation API improvements address developer complaints about managing long-lived async tasks in SPAs.
This release also fixes several bugs in anchor positioning, multi-column layouts, and other CSS features, based on testing on real-world websites.
What This Means
For developers, Zstandard means reduced server load and faster delivery of assets, especially for large text files. The Navigation API update simplifies complex state management in SPAs, reducing the need for custom cancellation logic.
For everyday users, pages will load faster, especially on slow networks. visionOS users get a more polished video experience. Overall, Safari 26.3 advances both performance and developer tools, reinforcing Apple's commitment to modern web standards.