Liquid Glass (SwiftUI, iOS 26)

Apple's iOS 26 Liquid Glass material in SwiftUI — a translucent, refractive layer that floats UI above content and morphs as it moves. The deep reference (the 3 Cs, the core .glassEffect API, GlassEffectContainer batching, glassEffectID morphing, glass button styles, background-extension/scroll-edge effects, tab bar & navigation, sheets, animation, common patterns, anti-patterns, fallbacks, accessibility, migration, checklist) lives in references/guide.md. This file is the decision and discipline layer: read it first, open the guide for specifics.

Currency note (2026-06-02): the iOS 26 API is .glassEffect(_:in:) plus GlassEffectContainer, .glassEffectID(_:in:), and .buttonStyle(.glass) / .glassProminent. .glassBackgroundEffect() is the visionOS modifier — not the iOS API — so never reach for it on iOS. The bundled guide uses the correct .glassEffect family throughout, verified against Apple's SwiftUI docs.

Dials

Set these explicitly at the start; they change what "correct" means.

1. ADOPTION — system-default (default; adopt SDK 26, let the system glass the standard nav bar, tab bar, toolbars, sheets — touch nothing) · opt-in-effects (add .glassEffect/.buttonStyle(.glass) to a few custom floating controls) · full-custom (bespoke morphing glass clusters, glassEffectID, glassEffectUnion — only when the design truly needs it).
2. CONTAINER_BATCHING — single (one isolated glass element, no container needed) · container (default for two or more nearby glass elements; wrap them in GlassEffectContainer(spacing:) so they render together, share sampling, and can morph). Multiple loose .glassEffect views without a container is the #1 perf/visual mistake.
3. FALLBACK — none (deployment target is iOS 26+, no branch needed) · graceful (default when supporting < iOS 26; gate glass behind if #available(iOS 26, *) and fall back to .ultraThinMaterial / .regularMaterial so older OSes stay legible).

When to use

Building or reviewing any SwiftUI surface that adopts iOS 26 Liquid Glass: glassy custom controls, floating buttons, morphing toolbars, hero headers under a translucent nav bar, or a migration of .ultraThinMaterial UI to the new material. Pair with swiftui-pro for the surrounding SwiftUI architecture, state, and performance review — this skill owns the glass material specifically.

Core rules