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Your DSP has two ways to deliver the ad creative for a bid. Pick the one that matches how your creative pipeline works.

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The two paths

Include the creative directly in your bid response under ad_data. The SSP serves it as-is when you win and never calls your render endpoint for that bid. 
{
  "data": {
    "bid": 7.50,
    "bidId": "bid_abc123",
    "ad_data": {
      "headline": "Premium Running Shoes",
      "description": "Perfect for marathon training.",
      "url": "https://your-dsp.com/click/abc123",
      "advertiser": "Nike",
      "domain": "nike.com",
      "image_url": "https://cdn.nike.com/ad.png"
    }
  }
}
One round-trip per auction. Lower latency, simpler operations, and the SSP doesn’t need to reach back out to you.

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Path B: Render endpoint

Return only bid + bidId in the bid response. If you win the auction, the SSP calls your /render-ad endpoint with the bidId and clearing price; you respond with the creative there. 
// Bid response — no ad_data
{ "data": { "bid": 7.50, "bidId": "bid_abc123" } }

// Later, if you win, SSP POSTs to your /render-ad
{ "bidId": "bid_abc123", "realizedPrice": 7.50 }
Two round-trips, but only on wins. Useful when creative generation is expensive (e.g. LLM-written copy, dynamic image composition) and you don’t want to do that work for every bid — only for the ones you win.

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When to use which

SituationRecommended path
You have static, pre-built creatives in a catalogPre-rendered — fastest path, no reason to defer.
Your creative is templated and cheap to produce per-bidPre-rendered — render cost is negligible vs the extra round-trip.
Your creative requires a per-impression LLM call or expensive generationRender endpoint — defer the work until you’ve won.
You need to know the clearing price before finalising the creativeRender endpoint — realizedPrice is only available on render.
You’re under tight latency budget and your creative is readyPre-rendered — saves one HTTP hop on every win.

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Strict validation applies to both paths

Whichever path you choose, the SSP validates the creative against the same schema:
  • ad_data in the bid response (Path A)
  • data in the render response (Path B)
Both use strict validation (extra="forbid") and reject unknown fields. A failed validation drops the bid — no second chance, even if your bid was the highest. See the API Reference for the exact field schemas.

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Mixing paths

You can choose per-bid. Some bids can include ad_data, others can omit it and rely on /render-ad. The SSP decides per response: if ad_data is present and valid, render is skipped; otherwise it calls /render-ad. This means you can:
  • Default to pre-rendering for cheap creatives.
  • Fall back to the render endpoint only for bids that need just-in-time generation.
You don’t have to pick one path globally.