You are probably paying a 30-50% tax on every programmatic dollar you spend, and most of it goes to intermediaries you have never evaluated. That is not speculation. The ISBA/PwC programmatic supply chain study found that ad tech fees consume up to half of advertiser spend before a single impression reaches a publisher. In 2026, with US programmatic display spending projected to exceed $203 billion (eMarketer), even a 5% improvement in supply path efficiency translates to real money.
Supply Path Optimization (SPO) is how you fix this. It is the practice of analyzing every route your bids take from DSP to publisher, identifying the paths that waste money or add latency, and cutting them. This guide walks you through a full supply chain audit, step by step.
What SPO actually solves
When you bid on an impression through your DSP, that same ad slot might be available through five, ten, or even fifteen different SSPs. Each one adds its own fee, its own auction mechanics, and its own latency. According to Jounce Media's 2025 State of the Open Internet report, the average publisher now authorizes over 450 supply paths through their ads.txt file, a threefold increase since 2020. Rebroadcasting supply chains account for 37% of display auctions and 32% of video auctions.
This means you are often bidding against yourself for the same impression across multiple paths, paying different fees each time. SPO fixes that by mapping your actual spend paths and pruning the ones that do not earn their keep.
Prerequisites before you start
You will need:
- Log-level data from your DSP. Bid logs, win logs, and spend-by-SSP reports. If your DSP does not give you this, that is your first problem.
- Access to your ads.txt/sellers.json verification tools. The IAB Tech Lab standards (ads.txt 1.1, sellers.json, and the SupplyChain object) form the backbone of any legitimate audit.
- A spreadsheet or BI tool. This is analytical work. You need somewhere to model the data.
- 30-90 days of historical spend data. Anything less and you are making decisions on noise.
Step 1: Map your current supply paths
Pull a full report from your DSP showing spend broken down by SSP, exchange, and seller type (DIRECT vs. RESELLER). In The Trade Desk, this is available through the Authorized Supply Path reporting. In DV360, check your marketplace reports with supply path dimensions enabled.
What you are looking for:
- How many SSPs are you buying from?
- What percentage of spend goes through DIRECT vs. RESELLER paths?
- Are there SSPs where you are spending money but seeing poor win rates or high CPMs?
Expected output: A table with columns for SSP name, spend, impressions, win rate, average CPM, and seller type. If you have more than 15-20 active SSPs, you almost certainly have redundancy.
Step 2: Run an ads.txt and sellers.json audit
For every SSP in your supply path, verify two things:
-
Is the SSP listed as DIRECT in the publisher's ads.txt file? Navigate to
publisher.com/ads.txtfor your top 20 publisher domains by spend. A DIRECT listing means the publisher has a first-party relationship with that SSP. A RESELLER listing means there is at least one intermediary. -
Does the SSP's sellers.json file list the publisher correctly? Check
ssp-domain.com/sellers.jsonand confirm the publisher appears with accurate domain and name information.
If you find SSPs where the publisher relationship is listed as RESELLER but you are paying similar fees to DIRECT paths, that is a path to cut. You are paying intermediary fees for no additional value.
Tip: Automate this check. Manually visiting ads.txt files for hundreds of publisher domains does not scale. Tools like Jounce Media's supply chain analysis, or your own scripts that crawl and parse ads.txt files, save days of work.
Step 3: Analyze auction dynamics
Not all SSPs run their auctions the same way. Some run first-price auctions with bid shading. Others have complex fee structures that are not immediately visible. Pull your bid-level data and look at:
- Clearing price vs. bid price: A consistent gap between what you bid and what you pay suggests healthy bid shading. If you are paying close to your max bid through a particular SSP, their auction mechanics may not be working in your favor.
- Fee transparency: Ask each SSP to disclose their take rate in writing. The IAB Programmatic Fee Transparency Calculator provides a framework for this. If an SSP will not tell you their fee structure, that tells you what you need to know.
- Match rates: How well does each SSP's audience data match your targeting segments? Low match rates mean you are buying a lot of impressions outside your intended audience.
Step 4: Score your SSPs
Build a scorecard. Here is what to include:
| Metric | Weight | What good looks like |
|---|---|---|
| Direct publisher relationships | 25% | 70%+ DIRECT in ads.txt |
| Fee transparency | 20% | Published take rates, clear reporting |
| Win rate | 15% | Consistent with your other SSPs |
| Unique inventory | 20% | Provides access to publishers you cannot reach elsewhere |
| Match rate | 10% | 60%+ audience match on targeted campaigns |
| Fraud/IVT rate | 10% | Under 2% invalid traffic |
Weight these based on your priorities. If you are a brand safety-first buyer, increase the fraud/IVT weight. If you are optimizing for cost, weight fee transparency higher.
Step 5: Cut paths and measure the impact
This is where most teams stall. They build the scorecard but never actually cut anyone. Do it.
Start with SSPs that score in the bottom 20% of your scorecard. Pause spend through those paths for 30 days. Monitor:
- Did your CPMs change? (They usually drop slightly because you are eliminating the duplicated auction pressure.)
- Did your reach decrease meaningfully? (Rarely, because most of those impressions were available through your remaining SSPs.)
- Did your win rates improve? (Often yes, because you are bidding through fewer, more efficient paths.)
After 30 days, make the cuts permanent or adjust. Then repeat with the next tier.
Where AI fits in 2026
The major DSPs now have built-in SPO features that handle routine path optimization automatically. The Trade Desk's Authorized Supply Path prioritizes DIRECT seller relationships and known-good paths. DV360 offers supply path controls that let you set preferences for directness and transparency.
These tools handle the baseline well. They will avoid obvious reseller chains and deprioritize SSPs with poor transparency signals. But they are not a substitute for the strategic audit described above.
AI handles the monitoring. You handle the strategy. Let your DSP's algorithms flag anomalies in supply path performance. Use them to automate bid routing once you have established which paths you trust. But the decisions about which SSPs to keep, which to cut, and how to weight your priorities are still human calls.
As Basis Technologies noted in their 2026 programmatic trends report: advertisers should leverage AI for routine monitoring while reserving human expertise for strategic oversight and decision-making. That tracks.
Common mistakes to avoid
Optimizing only for the shortest path. Direct is not always best. Some RESELLER paths provide access to premium inventory you cannot get otherwise. The goal is the most value-preserving path, not the most direct one.
Running the audit once and forgetting it. The supply chain changes constantly. Publishers add and remove SSPs. Fee structures shift. Run a full audit quarterly, with automated monitoring in between.
Ignoring CTV and in-app. SPO started in display, but CTV and in-app supply chains are even messier. CTV inventory sharing agreements (where content owners distribute through multiple platforms) create complex ads.txt relationships that need dedicated attention.
Cutting too aggressively. If you remove too many paths at once, you lose the ability to isolate what worked. Cut in tiers. Measure between each round.
The bottom line
SPO is operational work, not a one-time project. The teams that treat it as an ongoing discipline consistently outperform those that run a single audit and move on. Jounce Media's data shows that durable, well-maintained supply chains capture 64% of RTB bid requests and 69% of DSP gross ad spend. The market already rewards buyers who put in the work.
Start with Step 1. Pull your supply path report this week. You will probably be surprised by what you find.
Sage Thornton writes technical guides for The Daily Vibe.
