From 15 October 2026, Google Ad Manager fills the standard OpenRTB category fields, site.cat, site.pagecat, app.cat and app.pagecat, in bid requests to Authorized Buyers, Open Bidding partners and SDK bidders. It applies only outside the EEA, the UK and Switzerland, it is on by default, and one network-level toggle turns it off.
That is the whole announcement. What it does to your numbers is a different question, and the answer depends on what your pages are about, where your readers are, and whether your Prebid bidders already get the same signal from you.
What changes in the bid request on 15 October
Since February 2020, Google has not passed contextual content categories to the buyers in its auction. It removed them after talks with European data protection authorities, and the industry mostly shrugged at the time, because buyers could crawl the page URL themselves. For six years, a DSP bidding through Ad Exchange or Open Bidding has had to work out what your page was about on its own, or not bid on the basis of content at all.
From Thursday, the request carries it again, in the standard fields:
| Field | What it describes | Where it appears |
|---|---|---|
site.cat |
The site as a whole | Web requests |
site.pagecat |
The page being viewed | Web requests |
app.cat |
The app as a whole | In-app requests |
app.pagecat |
The screen or content being viewed | In-app requests |
Google's help page says the fields use IAB taxonomies. In OpenRTB 2.6 a separate field, cattax, names the taxonomy the codes come from, and if it is missing the buyer is meant to assume IAB Content Category Taxonomy 1.0. The Authorized Buyers integration guide lists IAB Content 1.0 and Google's own category list as the supported cattax values. If you run a DSP connection of your own or talk to a buyer's engineering team, that is the line to point them at.
Two limits apply. Requests from the EEA, the UK and Switzerland do not carry the fields at all for now. Categories that could relate to the special categories of data in GDPR Article 9 (health, religion, sexual orientation, political opinion and the rest of that list) are not shared from anywhere.
Who gets the categories, and who does not
The change is about the requests Ad Manager builds. That matters for anyone running Prebid next to Google demand.
| Demand path | Receives the categories from 15 October | Who controls it |
|---|---|---|
| Ad Exchange (Authorized Buyers) | Yes, outside EEA, UK, CH | Google, toggle in Ad Manager |
| Open Bidding partners | Yes, outside EEA, UK, CH | Google, toggle in Ad Manager |
| SDK bidders (in-app) | Yes, outside EEA, UK, CH | Google, toggle in Ad Manager |
| Prebid.js bidders | Only what your wrapper sends | You, in pbjs.setConfig |
| Direct and PG line items | Not an auction signal | Your trafficking |
Prebid bidders see what you put in ortb2.site. The Prebid first-party data docs list cat, sectioncat and pagecat as standard site fields you can set globally with setConfig, per auction in requestBids, or per bidder with setBidderConfig. A lot of wrappers set none of them. Run this in the console on an article page:
pbjs.getConfig('ortb2')
If site has no cat or pagecat, then from Thursday the Ad Exchange buyers on your non-European traffic know more about the page than your Prebid bidders do. Whether that moves money depends on which buyers price on content, which you find out from the reports below and not from a guess.
Should you leave the toggle on?
The toggle is called "Share contextual category signals" and sits under Admin, Global settings, Network settings, in the "Ad preference settings" section. Leaving it on is the default and asks nothing of you. Here is how the decision usually splits.
Leave it on if most of your pages sit in categories buyers pay for: finance, autos, travel, technology, food. A buyer who can see "personal finance" in the request can bid for that context without its own crawler, and the page that used to be priced as generic news inventory may now clear a higher bid.
Look harder if a large share of your inventory is hard news: crime, conflict, disasters, politics. Buyers running brand safety rules can now exclude those categories at bid time with less effort than before. Some of them already did it through URL crawling, some did not. If your section fronts and breaking news pages earn less after Thursday while lifestyle pages earn more, the categories are working exactly as designed, and the net is what you have to judge.
Switch it off only with a reason in the numbers. Turning off a signal buyers can use to price your pages should be a measured decision, not a privacy reflex, because the European traffic and the Article 9 categories are already excluded by Google.
The report that tells you whether it paid
The European exclusion is useful: it gives you a control group. Your EEA, UK and Swiss traffic keeps the old bid request, and the rest of the world gets the new one. Same pages, same week, same buyers. If something moves outside Europe and not inside it, the categories are the most likely cause.
Build this as a saved report in Ad Manager reporting:
- Dimensions: Date, Country, Demand channel, Ad unit (or your section key-value if you have one).
- Metrics: Ad requests, Impressions, Revenue, and revenue per 1,000 ad requests as a calculated column.
- Filter Demand channel to Ad Exchange and Open Bidding. Run a second copy for header bidding.
- Date range: 14 days before 15 October and 14 days after. Compare the same weekdays, not the day before against the day after.
- Group the countries into two buckets: EEA, UK and Switzerland in one, everything else in the other.
Then read it in this order:
- Revenue per 1,000 ad requests for Ad Exchange, outside Europe, after versus before. Do the same for the European bucket. The difference between the two changes is your estimate of what the categories did.
- The same split by section. A rise on lifestyle and finance with a fall on news is the brand safety pattern from the previous section, and it tells you which pages buyers are now pricing on content.
- Header bidding revenue per 1,000 requests outside Europe. If Ad Exchange rose and Prebid did not, your Prebid bidders are bidding on a thinner request than Google's buyers now see, and adding
catandpagecattoortb2.siteis the next test. - Ad Exchange win share against Prebid on the same ad units. A shift toward Google outside Europe with no change inside it is the categories moving the auction between your two demand paths.
Two weeks is enough to see a direction, not to settle it. Keep the report and look again at four weeks, after the first month-end budget cycle.
If you decide to send categories to Prebid too
A per-page category is something your CMS already knows: the section, the tags, the article type. Mapping your sections to IAB Content Taxonomy codes once, and writing them into ortb2.site.cat and ortb2.site.pagecat on each page, gives every Prebid bidder the same signal Google's buyers now get. Set cattax so bidders know which taxonomy you used. Do it on a share of traffic first and compare header bidding revenue per 1,000 requests by bidder against the pages without it. Some bidder adapters pass the fields through and some do not, and the per-bidder report is how you find out.
Keep the mapping honest. A news page tagged as travel to pull a higher bid will be caught by the buyer's own crawler, and the cost lands on your domain's reputation with that buyer, not on the page.
What to do this week
- Check the toggle in Ad Manager global settings and decide on purpose, before Thursday.
- Save the report above with a 15 October annotation in whatever you use for change logs.
- Run
pbjs.getConfig('ortb2')on an article page and a section front. Write down what your Prebid bidders get today. - On 29 October, read the two-bucket comparison. Decide on Prebid categories from that, not from this post.
Optimon reads your own Ad Manager and Prebid data together, so a change like this one shows up the next morning as a ranked cause, by country bucket and by section, with the numbers attached.
FAQ
What exactly changes in Google Ad Manager on 15 October 2026?
Ad Manager starts filling the standard OpenRTB category fields (site.cat, site.pagecat, app.cat and app.pagecat) in the bid requests it sends to Authorized Buyers, Open Bidding partners and SDK bidders. Until now buyers had not received contextual categories from Google since February 2020. No action is needed for sharing to start.
Does the change apply to traffic from Europe?
No. For now the fields are sent only on requests from outside the EEA, the UK and Switzerland, and categories that may relate to the special categories of data in GDPR Article 9 are never shared. That split gives you a built-in comparison group in your own reports.
Does this send categories to my Prebid bidders too?
No. The change covers the bid requests Ad Manager builds for its own demand. Prebid bidders receive whatever your wrapper puts in ortb2.site, so if you want them to see categories you set cat, pagecat and the taxonomy yourself in setConfig.
Sources
- Standard OpenRTB contextual signal sharing (Google Ad Manager Help)
- What's new in Google Ad Manager (Google Ad Manager Help)
- Additional steps to further safeguard user privacy (Google, on removing contextual categories from bid requests in 2020)
- Industry shrugs as Google announces plans to restrict contextual data (AdExchanger)
- Google will restrict contextual data in real-time ad bids (Marketing Dive)
- OpenRTB 2.6 specification (IAB Tech Lab)
- OpenRTB integration guide (Google Authorized Buyers)
- First Party Data (Prebid.js documentation)
