The UCP Technical Council Just Shipped Attribution into Core. Here's What That Means.

On May 5, 2026 , the UCP Technical Council merged PR #391 into the spec's main branch — adding a top-level attribution field to cart, checkout, catalog, and order operations. The field carries platform-emitted referral and conversion-event context: campaign IDs, click identifiers ( gclid , fbclid , ttclid ), source/medium markers. Open string-keyed map. Universal across requests; not gated by capability negotiation. As UCP matures, attribution landing in core was always going to happen. Agentic