Svelte 5.57.0

Svelte 5.57.0 was released on August 28, 2026. This release adds new server rendering exports, a has helper for context, and several quality-of-life additions, while shipping a long list of fixes and performance improvements.

New Features

• Export RenderOutput, SyncRenderOutput, Csp and Sha256Source from svelte/server
• Add a has function to createContext
• Support defaultValue on select elements
• Add getOrInsert and getOrInsertComputed to SvelteMap

Fixes

The patch set addresses routing and reactivity edge cases, including blocking template store subscriptions, tracking SvelteDate snapshots in reactions, and removing svelte:head anchors on unmount. Route derived errors are now routed through the invoke error boundary, and ownership mutation ignores apply to binding assignments.

Performance

Several optimizations landed. The legacy style reactive statement ordering moves from quadratic to linear time, cached select option values are reused, and img loading is treated as a static element once again.