vCPM (viewable cost per thousand impressions)

The billing unit is the viewable impression, defined by the MRC standard Amazon cites: at least 50% of the ad's pixels in the viewport for one continuous second for images, 50% in view with two seconds of playback completed for video. Where Amazon cannot measure viewability directly it infers it from historical data and placement characteristics, so you are billed against measured-or-modelled views. It is a bid setting rather than a campaign type — Sponsored Display campaigns optimizing for viewable impressions (costType vcpm in the Ads API, which requires bidOptimization reach) and the Sponsored Brands grow-brand-impression-share goal; Sponsored Products is CPC-only. Despite the common claim, Amazon DSP is not a vCPM buy: its published bid controls are a base bid and an optional maximum average CPM, both per 1,000 impressions.

The trap is judging vCPM on the campaign row. vCPM billing is the only way a Sponsored Brands or Display campaign becomes eligible for view-through attribution, but Amazon attributes a conversion to no more than one ad interaction across all campaigns and all advertisers — promoted-ASIN clicks, brand-halo clicks, then views. Views eat last, so scaling your own click campaigns drops vCPM ROAS with the campaign untouched; judge it on a geo or audience holdout, or in AMC. Watch the denominators: billing is per 1,000 viewable impressions while the Impressions column counts impressions served, so spend divided by impressions lands below your bid. That is arithmetic, not a discount. From January 1, 2026, additional signals gate which views are eligible on some placements — expect view-attributed trend lines to move, not a repricing.