Understanding how the dominant ad server and the leading header bidding wrapper work together -- and where they compete. Updated 2026.
| Feature | Google Ad Manager | Prebid.js |
|---|---|---|
| Type | Ad server + ad exchange (Google AdX) | Header bidding wrapper (client-side) |
| Pricing | Free (Ad Manager) / Revenue share (Ad Exchange) | Free and open source |
| Primary Function | Manage inventory, serve ads, run auctions | Run parallel auctions across multiple SSPs |
| Demand Sources | Google AdX + third-party networks via line items | Any SSP with a Prebid adapter (200+) |
| Auction Type | Unified auction (server-side) | Client-side parallel auction before ad server |
| Video Support | Full VAST/VPAID/IMA | Prebid Video with VAST support |
| Publisher Control | Google-managed platform | Full publisher control, open-source code |
| Market Share | ~90% of major publishers | ~70% of header bidding publishers |
| Relationship | Can work together (most common setup) | Sends winning bid to GAM as a line item |
| Maintained By | Prebid.org (open-source community) |
Despite appearing in "vs" searches, Google Ad Manager and Prebid.js are not direct competitors -- they most commonly work together. The typical publisher setup uses Prebid.js to run a client-side header bidding auction across multiple SSPs, then passes the winning bid to Google Ad Manager to compete against Google's own demand (AdX) and any direct campaigns.
This combination gives publishers the best of both worlds: broad demand competition from header bidding and the robust ad serving, reporting, and direct deal management of GAM.
Google Ad Manager (GAM) is the industry-dominant publisher-side ad server, used by approximately 90% of major publishers. It handles:
GAM is free for small publishers and operates on a revenue-share model for larger publishers accessing Ad Exchange demand.
Red Volcano tracks adoption of both technologies across 32M+ publishers.
Explore the Data →Prebid.js is the leading open-source header bidding wrapper, maintained by Prebid.org. It runs in the browser and enables publishers to:
Before header bidding, publishers used a sequential waterfall where SSPs were called one at a time. Prebid.js helped eliminate this inefficiency, typically increasing publisher revenue by 20-50%.
The standard implementation flow:
This setup maximizes competition and revenue while maintaining GAM's role as the final decisioning engine.
Most publishers benefit from using both. GAM serves as the ad server and provides Google demand, while Prebid.js adds competition from other SSPs. Together, they maximize revenue. However, smaller publishers may start with GAM alone.
Yes. Prebid.js is free, open-source software maintained by Prebid.org. There is no licensing fee. However, you may incur costs from managed Prebid services or from the SSPs you work with.
Yes, Prebid.js can work with other ad servers, but GAM is by far the most common pairing. Some publishers use Prebid with ad servers from Xandr, Kevel, or custom solutions.
GAM includes Open Bidding (formerly Exchange Bidding), which is Google's server-side header bidding alternative. However, many publishers prefer Prebid.js for its transparency and broader SSP support, often running both.
Most publishers see optimal results with 5-10 Prebid demand partners. Adding more increases competition but also page latency. The ideal number depends on your traffic volume, geography, and inventory type.
Red Volcano monitors adoption of every major ad technology, SSP, and header bidding solution. See market share trends, publisher-level data, and competitive intelligence.