The story. The Trade Desk cannot currently serve ads to Safari users on iOS 27, released 14 September, because Apple added adsrvr.org, the DSP’s core ad request and delivery domain, to its block list. Apple has been investigating since last week and has not resolved it. (AdExchanger, Apple’s Latest Operating System Blocks The Trade Desk From Serving Ads On Safari, 29 September 2026)
01What happened
- Identity vendors were blocked alongside it. iOS 27 extends Apple’s block on data broker domains. Newly listed are UIDAPI.com (Unified ID 2.0), ID5, Audigent, LiveRamp and Permutive.
- The serving domain is a different case. TTD engineer Ian Meyer wrote on GitHub that adsrvr.org is “core ad request and delivery domain, not identity.” Blocking it shuts the DSP out of Safari inventory on the latest iOS.
- Apple has not committed to a fix. WebKit’s John Wilander said he saw the flag and would investigate. As of Monday his only update was that he would tell TTD if changes are ready to test.
- The evidence is bid-level. TTD’s bug report includes a yahoo.com ad call where its bids were blocked while Google’s, on ad.doubleclick.net, went through cleanly.
- Neither company commented. Neither Apple nor The Trade Desk responded to AdExchanger before publication.
02What it means inside a GAM network
On the sell side this shows up as missing demand, not an error. A DSP whose calls are blocked in the browser never returns a bid, so a Safari-on-iOS 27 segment can lose one of the largest buyers while the rest of the auction runs as normal. The visible effect is lower bid density and lower clearing prices on that traffic, which looks like softer demand instead of a blocked domain.
Other buyers see the same auction. Google’s bids cleared in TTD’s own bug report, so the block favors a competitor on the affected traffic. Apple has previously made targeted tracking changes that hurt Meta and Criteo. The pattern is that a browser vendor can reprice a publisher’s inventory by editing a list.
The best case is that Apple blocked a root ad-serving domain by accident and reverses it.
03What publishers should do about it
04The bottom line
The best case is that Apple blocked a root ad-serving domain by accident and reverses it. The worse one is that WebKit keeps it, and a large DSP loses Safari on new iOS. Either way, publishers holding Safari inventory should know what their demand looks like on iOS 27 before someone else explains it.