How Google Open Bidding (EBDA) Works and How It Compares to Prebid

Google Open Bidding (formerly Exchange Bidding Dynamic Allocation, or EBDA) runs server-to-server programmatic auctions inside Google Ad Manager without any on-page JavaScript. You enable demand partners in GAM, Google handles the auction server-side, and winning bids compete against AdX and your Prebid line items in a unified first-price auction. This article covers the mechanics, the fee structure, the transparency trade-offs, and why most high-yield publishers run Open Bidding and Prebid together rather than choosing one.

How Does Google Open Bidding Work Inside GAM?

Open Bidding lets you add third-party SSPs (Magnite, Index Exchange, PubMatic, OpenX) as demand sources inside Google Ad Manager's yield groups. When an ad request fires, GAM sends a server-to-server bid request to each Open Bidding partner simultaneously, collects responses, and evaluates them alongside AdX (Authorized Buyers) and any Prebid line items in a single unified auction.

The setup is entirely within GAM. Navigate to Delivery > Yield Groups > create a new yield group. Add your Open Bidding partners. Each partner requires a publisher account and a signed contract. Google handles the technical integration. You don't modify page code.

GAM's unified auction evaluates all demand sources in one first-price comparison. An Open Bidding partner bidding $7, an AdX bid of $6.50, and a Prebid line item targeting hb_pb=8.00 all compete in the same auction. The $8.00 Prebid bid wins. GAM doesn't favor its own demand. The highest valid net bid wins.

What Does Google Charge for Open Bidding?

Google takes approximately 5% of Open Bidding transaction revenue as a technology fee. If an Open Bidding partner bids $10 CPM, Google keeps roughly $0.50 and the publisher receives $9.50. This fee applies only to Open Bidding partner wins, not to AdX wins (which have their own separate fee structure) or Prebid line item wins (which carry no Google fee).

Compare this to Prebid: zero platform fees. Prebid is open-source under the Apache 2.0 license. You host the JavaScript. You manage the adapters. No intermediary takes a cut between the SSP's bid and your revenue. The SSP's own take rate still applies, but there's no additional wrapper-level fee.

The 5% fee sounds small until you scale it. On $50,000 monthly Open Bidding revenue, Google's cut is $2,500. Over a year, that's $30,000 in fees that wouldn't exist if the same demand came through Prebid adapters. Whether the convenience and latency benefits of Open Bidding justify that fee depends on your operational capacity to manage Prebid yourself.

How Does Open Bidding Compare to Prebid?

The two systems solve the same problem (getting multiple SSPs to compete for your inventory) through different header bidding architectures with different trade-offs.

Three differences matter most:

• Transparency. Prebid is fully inspectable. You see every bid, every response time, every clearing price. Open Bidding reports are filtered through GAM's interface. You see which partner won and at what price, but you don't get the granular bid landscape data that Prebid's console commands expose. You can't run pbjs.getBidResponses() on Open Bidding partners.
• Partner availability. Open Bidding supports roughly 20 Google-approved demand partners. Prebid supports 300+ bidder adapters. If an SSP you want isn't in Google's Open Bidding partner list, you can only reach them through Prebid.
• Fee structure. Prebid is free. Open Bidding takes ~5%. On identical bids, the Prebid path nets you more. The question is whether the operational cost of managing Prebid exceeds the 5% fee saving.

Should You Run Open Bidding, Prebid, or Both?

Run both. This isn't a diplomatic answer. It's the architecture that produces the highest yield for publishers with the operational capacity to manage it.

Open Bidding and Prebid are not mutually exclusive inside GAM. Prebid bids enter GAM as key-value-targeted line items. Open Bidding bids enter through yield groups. Both compete in the same unified auction. Adding Open Bidding partners on top of Prebid increases bid density without adding page latency.

The hybrid math: your 5 Prebid adapters generate an average winning eCPM of $6.00. Adding 3 Open Bidding partners introduces new demand that occasionally bids above $6.00. When an Open Bidding partner wins at $7.50, you receive $7.13 after Google's 5% fee. Still higher than the $6.00 Prebid bid it beat. Total yield increases because you've added auction pressure from sources that weren't previously competing.

Add Open Bidding partners that aren't in your Prebid config. That's where the incremental value lives.

What Do Most Publishers Get Wrong About Open Bidding?

Treating it as a Prebid replacement. Open Bidding supports fewer partners, charges a fee, and provides less transparency. It's a complement, not a substitute. Publishers who drop Prebid for Open Bidding alone typically see 5 to 15% revenue declines due to reduced bid density and the 5% fee.

Ignoring the net bid calculation. GAM compares Open Bidding bids after deducting Google's fee. An Open Bidding partner bidding $10 competes as a $9.50 net bid. If your Prebid line item targets $9.75, Prebid wins even though the Open Bidding gross bid was higher. This means Open Bidding partners need to bid 5% above Prebid bids to win, which creates a structural disadvantage for Open Bidding partners on equivalent inventory.

Not auditing partner overlap. If Magnite bids through both Prebid and Open Bidding, check whether both paths are active on the same impressions. Duplicate bid requests to the same SSP waste the SSP's QPS budget and can lead to throttling on one or both paths. Deduplicate by assigning each SSP to one path.

Monitor your Open Bidding yield against Prebid yield in GAM's historical reporting. Break it down by demand partner and compare against CPM benchmarks to identify where each path delivers unique value within your header bidding strategy. Use the CPM calculator to model the net revenue impact of adding or removing Open Bidding partners against your current Prebid baseline.