Prebid vs TAM vs Open Bidding.
The scored three-auction matrix — fees, auction location, log-level data, identity, control, latency, demand, roadmap — with every vendor-sourced number labeled as vendor-sourced.
Prebid, Amazon's Transparent Ad Marketplace (TAM), and Google Open Bidding are the three auction layers publishers use to make demand sources compete for the same impression. Prebid is open source and publisher-run; TAM runs on Amazon's servers; Open Bidding runs inside Google Ad Manager. They differ on fees, data access, and control.
Nearly every ranking comparison of these three is written by a party selling one of them. This page scores them on the record — and says plainly where the record is silent.
Fast read
- What this is
- A scored, vendor-neutral comparison of the three auction layers publishers run: Prebid (open source, publisher-operated), Amazon Transparent Ad Marketplace (server-side, Amazon-operated), and Google Open Bidding (server-side, inside Google Ad Manager).
- The fee answer
- Prebid: $0 license — the real costs are engineering and hosting. TAM: 2.5% of net revenue charged to SSP bidders since May 2023 (vendor-stated). Open Bidding: Google does not publish the rate; 5% display / 10% video-and-app per 2019 reporting.
- The control answer
- Prebid gives total code control and member-elected governance. TAM is a tag-only managed service with Amazon controlling the roadmap. Open Bidding is configuration inside GAM with Google controlling the roadmap.
- What it is not
- Not an either/or. Most large publishers run Prebid plus at least one of the other two — the real decision is which exchange goes through which path, because DSPs now suppress duplicate bids.
- Best for
- Publisher revenue, ad ops, and engineering leads choosing an auction stack — or renegotiating one after a fee change.
- Watch-out
- Every widely ranked comparison of these three is written by a party selling one of them. Numbers here are labeled vendor-stated, trade-reported, or not publicly documented.
The three-auction matrix, scored.
Nine dimensions, scored for publisher favorability. Labels are part of the data: vendor-stated means the vendor's own page is the only source; trade-reported means journalism, not documentation; not publicly documented means exactly that — no guessing.
| Dimension | Prebid | Amazon TAM | Google Open Bidding |
|---|---|---|---|
| Fee | $0 license; real costs are engineering time and Prebid Server hosting. Managed wrappers re-add a 10–20% share (trade-reported, not a standard). Best of the three on cost transparency. | 2.5% of net revenue charged to SSP bidders since May 2023 (vendor-stated; was $0.01 CPM). Who ultimately absorbs it is negotiated per SSP–publisher pair — not publicly documented. | Not published. Google's docs say only that payments are made net of Google's revenue share; 5% display / 10% video-and-app per 2019 reporting. Worst of the three on fee disclosure. |
| Auction location | In the browser (Prebid.js), or server-side via Prebid Server for apps, AMP, and heavy setups. | Client-initiated via the APS tag; the auction executes on Amazon's servers (vendor-stated). | Fully server-side inside Google Ad Manager: a unified first-price auction via dynamic allocation where the highest net bid — after Google's share — wins. |
| Log-level data | Full — the publisher owns the code and can attach ~50 analytics adapters. Most granular of the three. | "Auction-level reporting" with bidders, bid CPMs, and winners (vendor-stated). Whether that equals raw log files is not publicly documented; 2019 reporting described sample audit logs. | Aggregated reporting in the GAM UI. Granular bid data requires GAM 360 Data Transfer files — and bid files can no longer be joined, per trade reporting. Least granular of the three. |
| Identity / TIDs | Publisher-controlled. TIDs off by default since Prebid.js 8 (June 2023); SSP-specific rather than global since v10.9. User ID modules run in-page — the highest match rates. | Server-side hop degrades cookie matching vs client-side; Amazon's identity handling inside TAM is not publicly documented in detail. | Keyed to the Google User ID with bidder- or Google-initiated cookie matching. One exchange reported ~50% lower match rates vs Prebid; another saw parity (trade-reported, 2019). |
| Code control | Total: version, modules, timeouts, floors, activity controls. The cost is that you maintain it. | Tag-only: the single technical requirement is the APS multi-slot tag (vendor-stated). No code control. | None: "no additional technical development required" — and no customization beyond GAM yield-partner settings. |
| Latency | Client-side, subject to browser connection limits; docs recommend a ≤1,000 ms auction timeout and ≤3,000 ms failsafe. | Single server-to-server call; "decrease latency" is vendor-stated. One 2019 consultant measured 86% of responses within 500 ms — single-source. | Extended auction time of 160 ms inside GAM, up from the 100 ms Ad Exchange requirement (vendor-stated); ~60 ms added, 150–300 ms total per Google in 2019. |
| Demand access | 300+ bid adapters — the widest ecosystem. | 50+ SSP buyers plus Amazon DSP demand, which is effectively exclusive to APS — the main draw (vendor-stated counts). | 50+ exchanges as yield partners (written contract each) plus AdX — which is only reachable here. |
| Roadmap control | Member-elected committees; publishers literally voted the TID default flip. | Amazon, unilaterally — the 2023 fee change is the proof case. | Google, unilaterally. |
| Eligibility & payment | Anyone; SSPs pay the publisher directly (non-financial intermediary). | Invitation-only; requires your own ad server plus direct SSP contracts (UAM otherwise). Payment model: see the conflict noted below the table. | Requires GAM, an AdX account, and a contract per yield partner. Google is the financial intermediary and pays net 30 days. |
One documented conflict
Amazon's current TAM page claims one consolidated payment "in just 60 days" (vendor-stated), which contradicts historical descriptions of SSPs paying publishers directly under classic TAM. The change is not independently documented. Confirm the payment path in your own agreement rather than either description.
Follow the fee: the 2023 TAM repricing.
Most ranking comparisons still quote TAM's fee as $0.01 CPM. That number died in May 2023 — and the fight over who pays the replacement is the clearest available demonstration of what unilateral roadmap control costs.
| When | What happened |
|---|---|
| Until May 2023 | TAM charged SSP bidders $0.01 CPM per monetized impression — the figure most ranking comparisons still cite. |
| May 1, 2023 | Amazon replaced it with 2.5% of net revenue charged to SSPs; partners characterized the move as a 4–5% increase over the prior cost (trade-reported). |
| Mid-2023 | Index Exchange, Magnite, and PubMatic attempted to pass the fee to publishers as 2.5% payment reductions; Amazon said post-auction publisher charges violated buyer contracts. |
| Through Jul 31, 2023 | Amazon temporarily allowed pass-through with written per-publisher consent (a waiver). Who ultimately absorbs the 2.5% today is negotiated per SSP–publisher pair — not publicly documented. |
The other two fee facts worth holding onto: Amazon's UAM — the self-serve sibling for small and mid-size publishers — deducts its 10% fee from bids before the auction, so a $2.00 bid enters as $1.80 (vendor-stated); and Google's only published alternative to the undisclosed Open Bidding share is Direct Pay, a beta that bills the publisher a flat CPM instead (GAM 360 plus participating SSPs only).
Where the auction runs decides what you can see.
Auction location is not a plumbing detail — it determines your data access and identity match rates downstream.
- Prebid
In the browser (or Prebid Server)
Client-side runs typically 5–15 bidders inside a publisher-set timeout (docs recommend ≤1,000 ms). Because the code runs where you can watch it, you get full log-level data via ~50 analytics adapters — and in-page User ID modules deliver the highest identity match rates of the three.
- Amazon TAM
On Amazon's servers
One ad call from the page; the auction executes server-side (vendor-stated, with "decrease latency" as the pitch — one 2019 consultant measured 86% of responses within 500 ms, single-source). Reporting is "auction-level" per the current page; whether that equals raw log files is not publicly documented.
- Open Bidding
Inside Google Ad Manager
A unified first-price auction in the ad server itself, with a 160 ms extended auction window (vendor-stated). Identity keys to the Google User ID via server-side cookie matching — one exchange reported ~50% lower match rates vs Prebid (2019, trade-reported). Bid-level analysis requires GAM 360 Data Transfer, and bid files can no longer be joined.
Who should not use each.
Every one of these products is wrong for someone. The disqualifiers below come from the same primary record as the matrix — they are just the rows vendors do not lead with.
- Prebid
Do not run Prebid if…
You cannot staff wrapper ownership. There is no account manager: a stale adapter, a mis-set timeout, or an unmaintained floors module silently costs revenue. Outsourcing to a managed wrapper re-introduces a 10–20% share (trade-reported) — at which point the "free" argument is gone and you should compare on data access and control instead.
- Amazon TAM
Do not plan around TAM if…
You have not been invited — TAM is invitation-only and requires your own ad server plus direct SSP contracts; the self-serve alternative is UAM, a different product that deducts 10% from bids before the auction. Also skip it if you need documented raw log files (not publicly documented) or any say in the roadmap: the 2023 repricing was decided unilaterally and the pass-through fight landed on SSP–publisher contracts.
- Open Bidding
Do not choose Open Bidding if…
You are not on Google Ad Manager — it does not exist elsewhere. Skip it too if you require disclosed pricing (Google does not publish the revenue share) or bid-level analysis: granular data needs GAM 360 Data Transfer, and bid files can no longer be joined per trade reporting. It is the zero-effort path, priced accordingly and opaquely.
Running more than one: the duplication tax.
The three are additive, and large publishers commonly stack them. One vendor audit puts the split at roughly 70% of top publishers on Prebid.js, 15% on TAM, 15% on both — a claim with no published methodology, so treat it as directional at most.
The stacking cost is concrete: the same six exchanges reached through three wrappers can generate 18 identical requests to a DSP for a single impression. DSPs have responded — The Trade Desk is forcing exchanges to pick one supply path per format, with trade reporting expecting Prebid to win most of those picks. The working rule is one path per exchange per format: give each demand source exactly one route to your inventory, then let the wrappers specialize in what only they carry (Amazon DSP through APS; AdX through Open Bidding; everything else through Prebid).
Price the disclosure, not just the fee.
Across nine dimensions the pattern is consistent: what you gain in convenience you pay for in visibility. The rational stack prices that trade explicitly.
- An unpublished fee is not a low fee — it is an unpriced one. Google discloses no current Open Bidding rate; underwrite the 2019 figures as history, not terms.
- "Free" describes the Prebid license, not the cost of ownership. Price the engineering or price the managed share — never zero.
- Roadmap control is a pricing term. TAM's 2023 repricing and the pass-through fight showed the fee can move without your signature.
- Treat vendor latency claims as claims. Measure timeout distributions on your own traffic before crediting any wrapper with "faster."
- One path per exchange per format. DSPs now suppress duplicate bids; a stacked wrapper that duplicates demand is throughput, not revenue.
Frequently asked questions.
The questions behind the queries that reach this page — answered from the primary record, with sources linked below.
Is Amazon TAM really free for publishers?
Amazon charges the fee to SSP bidders, not publishers directly: 2.5% of net revenue since May 1, 2023 (vendor-stated; previously $0.01 CPM per monetized impression). In 2023 major SSPs tried to pass it to publishers as 2.5% payment reductions, Amazon objected, then temporarily allowed pass-through with written per-publisher consent. Who absorbs the 2.5% today is negotiated per SSP–publisher pair and is not publicly documented.
What percentage does Google take on Open Bidding?
Google does not publish the rate. Its current Ad Manager documentation says only that payments are made net of Google's revenue share. The widely cited figures — 5% for display and outstream, 10% for video and app — come from 2019 AdExchanger reporting, not any current Google document. A beta alternative, Open Bidding Direct Pay, bills the publisher a flat CPM fee instead of a revenue share (GAM 360 plus participating SSPs only).
Can you run Prebid, TAM, and Open Bidding at the same time?
Yes, and many large publishers do — the three are additive, not exclusive. The cost is bid duplication: the same six exchanges reached through three wrappers can generate 18 identical requests to a DSP for one impression. DSPs including The Trade Desk are forcing exchanges to pick one supply path per format, so the working rule is one path per exchange per format, with Prebid expected to win most picks (trade-reported).
Which of the three pays the publisher directly?
In Prebid and classic TAM, each SSP pays the publisher directly — the wrapper is a non-financial intermediary. Open Bidding and Amazon UAM route money through the platform: Google pays net 30 days per its feature brief. Note a conflict: Amazon's current TAM page advertises one consolidated payment in 60 days, which contradicts the historical per-SSP direct-payment description — the change is not independently documented, so confirm the payment path in your own agreement.
Which is best for a small or mid-size publisher?
Usually none of the classic three alone. TAM is invitation-only and assumes your own ad server plus direct SSP contracts — the small-publisher product is UAM, which deducts 10% from bids before the auction (vendor-stated). Without engineering, the realistic choice is Open Bidding (if on Google Ad Manager, unpublished rate) versus a managed Prebid wrapper (10–20% share, trade-reported): compare the effective take, not the marketing.
Where this connects.
Primary sources to validate.
Fees, docs, and product terms last validated: July 2026. Vendor fee models change without notice — the 2023 TAM repricing is the proof case. Validate every number on this page against the linked primary document before you negotiate.
Primary sources to validate 20 sources
- Prebid.org — What is Prebid? (official overview) ↗ Official docs
Free license, member-dues funding, 300+ bid adapters, ~50 analytics adapters, client vs Prebid Server architecture. Supports: fees, demand access, log-level data, code control.
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Recommended ≤1,000 ms internal auction timeout and ≤3,000 ms failsafe for Prebid.js. Supports: latency.
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Aug 2025 committee vote: TIDs SSP-specific rather than global, shipped in v10.9; ~1% of traffic on new logic as of Oct 2025. Supports: identity / TIDs.
- Prebid.js 8 release notes (TIDs off by default) ↗ Official docs
Publisher committee elected to flip the TID default to off in Prebid.js 8 (June 2023); opt-in via enableTIDs. Supports: identity / TIDs.
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Vendor-stated: 2.5% service fee charged to bidders, server-side auction from one ad call, auction-level reporting, 50+ buyers, consolidated 60-day payment claim. Supports: fees, auction location, log-level data, payment.
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Vendor-stated: UAM's 10% fee is deducted from bids before the auction; since Sept 1, 2023 Amazon Ads' own bids carry the same deduction. Supports: fees, UAM.
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No additional technical development required; 50+ yield partners; written contract per partner; aggregated reporting. States no revenue-share percentage. Supports: code control, demand access, log-level data.
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Payments made net of Google's revenue share, Google as financial intermediary. States no percentage — the disclosure gap this page labels. Supports: fees, payment.
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Unified first-price auction via dynamic allocation; highest net bid (after revenue share) wins; yield partners called via modified OpenRTB protobuf. Supports: auction location.
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Beta alternative fee model: Google bills the publisher a flat CPM fee instead of a revenue share; GAM 360 plus participating SSPs only. Supports: fees.
- Google Ad Manager — Open Bidding feature brief ↗ Official docs
Vendor-stated: extended auction time of 160 ms (up from the 100 ms Ad Exchange requirement); net-30 payment. Supports: latency, payment.
- Google Authorized Buyers — cookie matching guide ↗ Official docs
Server-side identity keyed to the Google User ID; bidder- or Google-initiated cookie matching for yield partners. Supports: identity / TIDs.
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2019 reporting: OB rev share at 5% display / 10% video-app; ~50% lower match rates on OB per one exchange; TAM sample audit logs; TAM latency consultant figures. Supports: fees, identity / TIDs, log-level data, latency.
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The 2023 TAM fee change: $0.01 CPM to 2.5% of net revenue, SSP pass-through attempts, Amazon objection, per-publisher consent waiver through Jul 31, 2023. Supports: fees, roadmap control.
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Context on the TID fight: some DSPs require TIDs as a condition for spend; cross-exchange dedup implications of SSP-specific TIDs. Supports: identity / TIDs.
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The Trade Desk forcing exchanges to pick one supply path per format; expectation that Prebid wins most picks. Supports: multi-wrapper reality.
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DSP-side duplicate-bid suppression — the mechanism that makes wrapper stacking throughput rather than revenue. Supports: multi-wrapper reality.
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TAM eligibility: invitation-only, own ad server, direct SSP contracts; UAM as the self-serve sibling. Supports: eligibility.
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Source of the 10–20% managed-wrapper revenue-share range — trade-reported, not a standard. Supports: fees.
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Claims ~70% of top publishers run Prebid.js, 15% TAM, 15% both. Vendor audit claim with no published methodology — treat as directional at most. Supports: multi-wrapper reality.
Platform capabilities and naming change quickly. Last validated: July 13, 2026. Check current documentation before implementation.Fees, docs, and product terms last validated: July 2026. Vendor fee models change without notice — the 2023 TAM repricing is the proof case. Validate every number on this page against the linked primary document before you negotiate.
Choosing — or restacking — your auction layers?
The work is pricing each path honestly: effective take per wrapper, one path per exchange per format, and a paper trail for every vendor-stated number before it reaches your forecast.