A migration checklist for re-bidding after an exchange flips to first-price

A migration checklist for re-bidding after an exchange flips to first-price

When an exchange moves from second-price (you pay just above the runner-up) to first-price (you pay exactly what you bid), your old bids overpay instantly. Re-tune in sequence.

1. Confirm the flip with evidence, not the announcement: in second-price your win price clusters below your bid; in first-price win price equals bid. Plot the win-price-to-bid ratio over time and watch it jump to 1.0.

2. Freeze bid changes for 48 hours and log a clean baseline of clearing prices under the new regime.

3. Estimate the clearing-price distribution per segment — the prices at which you actually won. Your new bid should target a percentile of that distribution, not your old second-price bid.

4. Introduce or re-tune bid shading specifically for this exchange; a shader calibrated on second-price history will systematically overpay until it relearns.

5. Validate by watching surplus (bid − clearing price). If surplus is large and stable, lower the target percentile until win rate just begins to soften.

Why it matters: The single most expensive moment in programmatic is the days after a silent first-price flip, when bids tuned for second-price auctions pay their full face value. A disciplined re-baseline-and-shade sequence stops the bleed before it compounds across a month of spend.