Timeout (tmax)

In real-time bidding a timeout is the maximum time an exchange or header-bidding wrapper will wait for bids before closing the auction, expressed in OpenRTB as the tmax field, "maximum time in milliseconds the exchange allows for bids to be received including Internet latency to avoid timeout."

tmax is set by the exchange in the bid request (OpenRTB 2.6, section 3.2.1). Typical values are 100 to 300 ms for display and longer for video and CTV. Prebid.js has its own timeout in requestBids, and Prebid Server passes a tmax downstream after subtracting its own processing time. A bid that arrives after the deadline is discarded, so from the bidder's side the timeout is a budget to be split between network round trip, request parsing, user lookup, model inference and response serialization.

The timeout is also an economic lever. A shorter tmax favors bidders with data centres near the exchange and penalises those that call external services during the auction. That is one argument for ARTF, which runs enrichment inside the host's data center instead of across a network hop; Adform's CTO put the comparison at 50 ms for a Trusted Match SLA against 20 to 100 ms for OpenRTB and 2 ms for Adform's internal systems, his own figures (PPC Land, 24 September 2026).

Example: an exchange sets tmax: 120; the network round trip to a bidder is 35 ms each way; the bidder has 50 ms for everything else and should alert if its 99th-percentile service time exceeds 40 ms.

Related: QPS, bid request, header bidding, Prebid Server.

Source: IAB Tech Lab, OpenRTB 2.6, BidRequest.tmax.

1. OpenRTB 2.6, section 3.2.1
2. PPC Land, 24 September 2026