Web compatibility in 2026: how to decide if you need a polyfill

Check Baseline before writing a fallback

Baseline classifies features by support across the core browser set. Newly available means recent interoperability; Widely available adds 30 months of availability. The 2026 list includes container style queries, :open, contrast-color(), @scope, shape(), view transitions and other APIs.

The May digest also moved the lh and rlh units, clip-path, :user-invalid and Navigator.userActivation to widely available.

Some things sit outside that list for opposite reasons: size container queries, :has() and popover are older and already taken for granted; anchor positioning and scroll-driven animations have not fully arrived yet.

Use Interop for what lands this year

Interop 2026 is the annual agreement between Apple, Google, Mozilla and Microsoft on what they will make work the same way. It was announced on 12 February with twenty focus areas. The ones that affect client work most: anchor positioning, container style queries, dialogs and popovers, scroll-driven animations, view transitions, attr(), contrast-color(), the Navigation API, scroll snap, shape() and zoom.

Interop is a shared work programme, not a promise that every listed feature is production-ready. A feature may still need a fallback until it ships in the versions used by your audience.

Review what each browser brought

Safari 27.0, of 17 September, lists 83 new features and 844 issues resolved. Three matter in production work: anchor positioning now takes transforms into account, appearance: base-select allows a <select> to be styled without rebuilding it, and the <model> tag reaches iPhone and Mac, which deserves its own article. It also brings WebGPU with clip distances.

Chrome 152, of 25 August, adds the alpha() colour function, a CPU performance API and subgroup size control in WebGPU, and removes the Private Aggregation API. Version 151, from July, brought two new performance entries, PerformanceSoftNavigation and InteractionContentfulPaint, and changed the initial value of position-anchor to normal. Version 146, from March, brought scroll-triggered animations and WebGPU compatibility mode.

Firefox 155, of 1 September, brings attr() with any value type, progress(), alpha(), font-width and QUIC version 2.

Do not change the metrics without a source

A fair amount has been written about a new Core Web Vitals metric in 2026. On the official web.dev page the thresholds are still LCP at 2.5 seconds, INP at 200 milliseconds and CLS at 0.1, measured at the 75th percentile, and the page carries October 2024 as its last updated date.

The new performance entries in Chrome 151 are measurement tools, not Google metrics. Until web.dev says otherwise, the thresholds stand.

Write the rule into each project

Set the policy at the start: the project's Baseline target, the audience coverage required and what happens when support is missing. For a public site, Widely available is a conservative starting point; Newly available can fit when usage data supports it.

A native feature may reduce JavaScript, but measure the effect before removing a library or polyfill. Check target browsers, tests and final code size.

If a site is still dragging polyfills from years back, tell us which browsers it has to support and what it loads today.