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 commerce can't operate as commercial infrastructure without a path for advertising and measurement context to flow alongside the transactional data — and the longer that gap stayed open, the more pressure would have built for vendors to ship incompatible parallel solutions. The merge isn't the surprising part. The interesting part is the specific shape of what shipped, and what its presence in core tells us about where the spec is heading.…