Bid caching

Bid caching is the reuse of a bid that arrived for an earlier auction on the same page in a later auction, as long as the bid has not expired.

Pages that refresh ad slots or load more content as the reader scrolls run many auctions in one visit. A bid that lost or went unused in the first auction may still be valid a few seconds later. Reusing it can fill a slot faster and without new requests. Prebid.js supports this in a narrow scope. The useBidCache setting was on by default in version 1.39 and has been off by default since Prebid.js 2.0, so publishers must opt in (Prebid.org, accessed 9 November 2026).

When caching is on, bidCacheFilterFunction decides which cached bids may be used. It runs only on bids from earlier auctions. Cached bids still obey their time-to-live. By default Prebid keeps every bid in memory until the user leaves the page, and minBidCacheTTL lets long-running pages drop stale bids sooner.

Buyers do not always welcome reuse. A bid priced for one moment may serve later, after the buyer's pacing or frequency counts have moved on.

Example: An infinite-scroll recipe site turns caching on but excludes video, with pbjs.setConfig({useBidCache: true, bidCacheFilterFunction: bid => bid.mediaType !== 'video'}). A display bid that lost on the first screen fills the fourth slot ten seconds later, inside its TTL.

Related terms: bid caching window, Prebid.js, header bidding, timeout, frequency capping.

Authoritative source: Prebid.org, "pbjs.setConfig", section "Use Bid Cache" (accessed 9 November 2026).

Read the full guide: Prebid.js guide: events, bidder adapters, releases and debugging.