Developer preview release notes: September 11, 2026

New

Add per-line custom data from product forms

Product forms can now set line-item attributes on add to cart. Use it for engraving text, gift notes, or custom options tied to that line.

The new hydrogen-cart-metafields skill covers storing custom cart data like delivery instructions.

Same-origin proxy for UCP requests

Caller-authenticated UCP MCP requests at /api/ucp/mcp now proxy to the configured Shopify store.

Keep packaged skills in sync after upgrades

npx @shopify/hydrogen skills sync copies the packaged skills into .claude/skills and .agents/skills. Reruns after an upgrade add new skills, update unmodified ones, remove ones the package no longer ships, and leave locally edited files alone unless --force is passed.

Projects that synced before this version need one sync --force to adopt the version stamp. skills check is the read-only version for CI.

Fixes

Canceled cart updates no longer print AbortError noise in the console when a newer update replaces them.

Migration

Compare the commits that bracket this release:

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