Sophie Blake
Publishers relying on Prebid for video header bidding are facing a significant operational change ahead of April 30, when Microsoft will shut down its public Prebid Cache service. The decision ends years of free infrastructure support that many publishers have quietly depended on to deliver video ads through Google Ad Manager (GAM), and it risks disrupting a large share of programmatic video inventory if migrations are not completed in time.
The Microsoft-hosted cache, originally built under AppNexus and later inherited through the Xandr acquisition, plays a critical but largely invisible role in video ad delivery. When a Prebid auction wins against Google’s own demand in GAM, the system must retrieve the video creative from a cache location in real time. Until now, Microsoft covered the cost of hosting those files. Once the cache is decommissioned, that responsibility shifts entirely to publishers and their partners.
Industry estimates suggest the impact could be widespread. More than 60% of Prebid-to-GAM video impressions currently rely on Microsoft’s cache endpoint, and GAM itself is used by the vast majority of U.S. publishers. Without an alternative in place, affected impressions may technically “win” auctions but fail to render, triggering VAST errors and resulting in lost revenue.
Microsoft has framed the move as a push toward local caching, a feature introduced in Prebid.js over the past year. Local caching stores video creatives directly in the browser using blob URLs, removing the need for third-party infrastructure and reducing network calls. From a performance perspective, this approach can improve load times and reduce failure points. However, it comes with trade-offs. Local caching does not fully integrate with Google’s Interactive Media Ads (IMA) framework, creating the risk of reduced AdX demand for publishers that depend heavily on Google’s exchange.
Other options exist, but none are frictionless. Several supply-side platforms and video vendors offer hosted Prebid caching as a paid service, which requires publishers to reconfigure their setups and absorb new costs. Building and maintaining in-house cache infrastructure is another path, though it demands engineering resources and ongoing operational oversight. Recent entrants have announced alternative cache solutions, but adoption remains limited and timelines are tight.
Complicating matters further, publishers experimenting with local caching have reported performance issues for bidders that already maintain their own server-side caches. In some cases, storing all bids locally appeared to interfere with existing bidder workflows, raising concerns about yield and auction efficiency. Meanwhile, undocumented workarounds within GAM have surfaced in developer discussions, but these solutions require additional customization and do not fully replace standard integrations.
The cache shutdown also lands amid broader instability in the header bidding ecosystem. Over the past year, disputes around transaction IDs, standards compliance, and competing forks of Prebid have already forced publishers to reassess long-standing technical assumptions. Microsoft’s decision adds another forced migration to that list, aligned with the company’s wider retreat from traditional ad tech, including the planned wind-down of its demand-side platform business.
With the April 30 deadline approaching, publishers that serve meaningful volumes of video through Prebid face a compressed decision window. Whether they choose local caching, paid third-party services, or self-hosted infrastructure, each option carries revenue, technical, and operational implications. For an industry accustomed to free, shared infrastructure, the end of Microsoft’s public Prebid Cache marks a shift toward higher costs and greater complexity in video ad delivery.
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