Interop 2026 sets the web platform’s interoperability agenda

A cross-browser effort coordinated by Apple, Google, Igalia, Microsoft, and Mozilla, Interop 2026 targets features that developers have ranked as most problematic. The project runs continuously against automated test infrastructure, and pass rates are visible on the Interop 2026 dashboard.

The 2026 focus areas draw directly from the top issues reported in the State of HTML and State of CSS surveys, which are tracked on webstatus.dev. Several items also appear among the top 20 requested features in the developer signals repository.

Rachel Andrew

Features prioritized by developer feedback

Most of this year’s focus areas are direct responses to pain points developers reported in the surveys. These include:

  • Anchor positioning: Makes it possible to place an element relative to another element’s position, such as a tooltip next to its trigger. The test set carries over unchanged from Interop 2025.
  • Container style queries: Conditionally applies styles based on the computed values of a container’s custom properties, using @container with one or more style() functions.
  • Scroll-driven animations: Advances animations tied to scroll position, via the animation-timeline, scroll-timeline, and view-timeline CSS properties.
  • Cross-document view transitions: This year’s view transitions work builds on the same-document support that became Baseline Newly available in Interop 2025, adding the blocking="render" attribute, <link rel="expect">, the :active-view-transition-type() pseudo-class, and fixes for cross-document transitions.
  • The attr() CSS function: Allows retrieving an HTML element’s attribute value, optionally typed or unit-bearing.

Dialogs and popovers

Interop 2026 homes in on the <dialog> element and the Popover API, specifically <dialog closedby>, the :open CSS pseudo-class, and the popover="hint" attribute, which defines a popover subordinate to other auto popovers—useful for tooltips.

Additional platform areas targeted for 2026

Beyond the survey-driven items, the roster includes broader platform work:

  • contrast-color(): Returns a color guaranteed to contrast against a specified foreground or background color.
  • Custom highlights: Styles arbitrary text ranges without injecting elements into the DOM.
  • Fetch uploads and ranges: Extends fetch() with ReadableStream uploads, better FormData and media handling, and support for the Range header.
  • IndexedDB: Focuses on the getAllRecords() methods in IDBObjectStore and IDBIndex for batched reads on large datasets.
  • JSPI for Wasm: Lets WebAssembly applications expecting synchronous calls work in asynchronous environments.
  • Media pseudo-classes: Includes :playing, :paused, :seeking, :buffering, :stalled, :muted, and :volume-locked for <audio> and <video> matching.
  • Navigation API: Continues interoperability refinements, including the precommitHandler option in navigateEvent.intercept(), which defers commit until a handler resolves.
  • Scoped custom element registries: The CustomElementRegistry() constructor enables separate registries, so custom elements with duplicate tag names can coexist.
  • Scroll snap: Governs panning and scrolling behavior inside a scroll container.
  • shape() CSS function: Defines shapes via line, move, and curve commands for use with clip-path and shape-outside.
  • WebRTC: Addresses remaining failures from the Interop 2025 focus area and builds on WebRTC interoperability.
  • WebTransport API: Uses HTTP/3 for client-server data transmission.
  • zoom CSS property: Continues from Interop 2025, as element scaling that affects page layout.
  • Web compat: Targets specific real-world problems such as ESM module loading, scroll event timing relative to animation events, and unprefixing the -webkit-user-select property.

Investigation efforts for future years

This year’s program also lays groundwork for features not yet ready for cross-browser testing:

  • Accessibility testing: Aims for consistent accessibility trees across browsers with improved WPT infrastructure.
  • JPEG XL: Defines testability requirements, including progressive rendering.
  • Mobile testing: Extends WPT infrastructure to cover mobile features like dynamic viewport changes.
  • WebVTT: Revises tests and documentation for conformance clarity.

Progress throughout the year can be followed on the Interop 2026 dashboard. Participating organizations have posted their own announcements: Apple, Igalia, Microsoft, and Mozilla.