Addressability is back, and this time the fight is over who owns the signal

The Prebid Summit on 13 October was supposed to be about auction mechanics and open-source tooling; it turned into a referendum on addressability in the wake of Apple's iOS 27 restrictions. Alan Chapell of the Monopoly Report framed the pivot: "The future challenge is going to be about addressability," forecasting that the "room for interpretation" in the Brinkema ruling on Google's ad tech means Google is likely to "claw back" some provisions. The sharpest sell-side argument came from The Trade Desk's Ian Meyers, who said the open web's transparency is being weaponised against it: "transparency is a significant liability. This is something that walled gardens don't have to deal with at the same level, because they're in charge of reporting back all the stats." Permutive CEO Joe Root offered the constructive counter, arguing publishers should copy Meta's post-Apple playbook: "What Meta did next is they rebuilt everything on top of their supply-side signals... they built this incredible outcomes engine off the back of it." Publishers, he said, are moving decisioning and audience intelligence onto the supply side to insulate themselves from unilateral platform policy. LUMA's Terry Kawaja and veteran Ari Paparo closed the session with a deflationary take on the "universal buying platform" hype: "I saw 'UMP' and I thought: ad network."

The crux

iOS 27 has resurrected the early-2020s addressability debate, but the power question has shifted from "can we track" to "who owns the signal the models are trained on," and the open web starts from a transparency disadvantage walled gardens do not carry.

Sell-side read

Root's argument is the actionable one: the publisher that can rebuild targeting on its own supply-side signals, authenticated and first-party, is the one that can demand premium CPMs when third-party identity keeps eroding, rather than waiting for a cookie replacement that is not coming.

Watch

Whether the court-ordered integration between Prebid and Google's ad tech actually separates AdX from Google Ad Manager, and whether Permutive-style supply-side identity gains real bidstream traction before the next platform policy change.