What is server-side header bidding?
Server-side header bidding runs the header bidding auction on a server instead of in the user's browser or app. The page makes a single call to the server, which contacts many demand partners at once and returns the winning bid. It reduces page latency and allows more bidders, but gives buyers fewer direct browser signals such as cookies.
Client-side header bidding sends separate requests from the browser to each bidder, slowing pages. Server-side header bidding, for example via Prebid Server or Amazon Publisher Services, moves that work to the cloud. It is standard in CTV and apps, where client-side code is impractical.
The trade-off is lower cookie-match rates, since bidders do not see the browser directly, which can reduce bid prices. Server-to-server setups also make it more important to pass accurate device and IP data, because fraudsters can exploit server-side traffic in the same way as SSAI spoofing.