Safari 26.4 adds Grid Lanes, WebTransport, and Keyboard Lock

WebKit released Safari 26.4 on March 24 with 44 web-platform features, 191 fixes, and one deprecation. The release overview centers on CSS Grid Lanes, WebTransport, Fullscreen Keyboard Lock, and a long set of layout and standards-alignment fixes.

Three additions address different application classes

Grid Lanes provides masonry-style placement within CSS Grid, aimed at galleries and feeds whose items have unequal heights. WebTransport adds low-latency bidirectional communication over HTTP/3 and QUIC, with reliable streams and unreliable datagrams available in one connection. Keyboard Lock lets a fullscreen application request keys that the browser normally reserves, useful for games, remote desktops, and creative tools.

The release also makes scroll-driven animations run on the compositor thread, completes WebKit’s blocks-in-inline layout rewrite, and begins broader work on a new Grid layout engine. These are engine changes with potential benefits for existing pages even when developers adopt no new syntax.

Verify fallback and recovery behavior

Each headline API has a failure mode worth testing. Grid Lanes needs a readable ordinary-grid fallback, especially when source order differs from the visual result. A WebTransport client needs connection timeout, retry, and a fallback transport for unsupported networks or browsers. Keyboard Lock must preserve a clear exit path and should never be the only way to reach essential controls.

This release also removes the deprecated FontFaceSet constructor. A dependency audit can catch rare direct use before users do. Teams supporting Safari should run representative MathML, SVG, zoom, anchor-positioning, and WebRTC cases because many fixes sit outside the three headline features. Start with the existing compatibility backlog: issues previously isolated to WebKit are the fastest way to learn whether 26.4 changes application behavior.