diff --git a/crates/trusted-server-js/lib/src/integrations/prebid/index.ts b/crates/trusted-server-js/lib/src/integrations/prebid/index.ts
index 826fec4b..d12ca614 100644
--- a/crates/trusted-server-js/lib/src/integrations/prebid/index.ts
+++ b/crates/trusted-server-js/lib/src/integrations/prebid/index.ts
@@ -193,6 +193,35 @@ function recordUserIdModuleDiagnostics(): PrebidUserIdDiagnostics {
 /** Resolved endpoint — set by installPrebidNpm, read by the adapter. */
 let auctionEndpoint = '/auction';
 
+// Prebid normalizes each bid into its own internal object during `addBidResponse`,
+// which can drop unknown top-level fields — so the custom `trustedServerRenderer`
+// descriptor set in `interpretResponse` may be gone by the time the `bidResponse`
+// listener runs (observed in production: the field is absent as early as `bidAccepted`).
+// To make registration independent of custom-field survival, the descriptor is also
+// stashed here keyed by `requestId` (a first-class field Prebid preserves) at
+// `interpretResponse` time, and the `bidResponse` listener falls back to it. Bounded.
+const MAX_PENDING_APS_RENDERERS = 256;
+const pendingApsRenderersByRequestId = new Map<string, unknown>();
+
+function stashPendingApsRenderer(requestId: unknown, renderer: unknown): void {
+  if (typeof requestId !== 'string' || requestId.length === 0) return;
+  if (
+    !pendingApsRenderersByRequestId.has(requestId) &&
+    pendingApsRenderersByRequestId.size >= MAX_PENDING_APS_RENDERERS
+  ) {
+    const oldest = pendingApsRenderersByRequestId.keys().next().value;
+    if (oldest !== undefined) pendingApsRenderersByRequestId.delete(oldest);
+  }
+  pendingApsRenderersByRequestId.set(requestId, renderer);
+}
+
+function takePendingApsRenderer(requestId: unknown): unknown {
+  if (typeof requestId !== 'string') return undefined;
+  const renderer = pendingApsRenderersByRequestId.get(requestId);
+  if (renderer !== undefined) pendingApsRenderersByRequestId.delete(requestId);
+  return renderer;
+}
+
 /**
  * Convert parsed {@link AuctionBid}s into Prebid bid response objects,
  * linking each bid back to the original BidRequest via `requestId`.
@@ -220,9 +249,12 @@ export function auctionBidsToPrebidBids(auctionBids: AuctionBid[], bidRequests:
     }
 
     const origReq = requestsByCode.get(bid.impid);
+    const requestId = origReq?.bidId ?? bid.impid;
+    // Stash by requestId so registration survives Prebid stripping the custom field.
+    if (renderer) stashPendingApsRenderer(requestId, renderer);
     return [
       {
-        requestId: origReq?.bidId ?? bid.impid,
+        requestId,
         cpm: bid.price,
         width: bid.width,
         height: bid.height,
@@ -524,12 +556,13 @@ function installApsBidResponseRegistry(): void {
 
   pbjs.onEvent('bidResponse', (rawBid) => {
     const bid = rawBid as unknown as Record<string, unknown>;
-    const renderer = bid[APS_RENDERER_FIELD];
-    if (
-      bid['adapterCode'] !== ADAPTER_CODE ||
-      bid['bidderCode'] !== APS_BIDDER_CODE ||
-      renderer === undefined
-    ) {
+    if (bid['adapterCode'] !== ADAPTER_CODE || bid['bidderCode'] !== APS_BIDDER_CODE) {
+      return;
+    }
+    // Prefer the custom field; fall back to the requestId stash when Prebid has stripped
+    // it during bid normalization (the field is often gone before this listener runs).
+    const renderer = bid[APS_RENDERER_FIELD] ?? takePendingApsRenderer(bid['requestId']);
+    if (renderer === undefined) {
       return;
     }
 
diff --git a/crates/trusted-server-js/lib/test/integrations/prebid/index.test.ts b/crates/trusted-server-js/lib/test/integrations/prebid/index.test.ts
index 68928785..a27be5f4 100644
--- a/crates/trusted-server-js/lib/test/integrations/prebid/index.test.ts
+++ b/crates/trusted-server-js/lib/test/integrations/prebid/index.test.ts
@@ -365,6 +365,49 @@ describe('prebid/installPrebidNpm', () => {
     );
   });
 
+  it('registers APS renderer via requestId when Prebid strips the custom field', () => {
+    installPrebidNpm();
+
+    const bidResponseListener = mockOnEvent.mock.calls.find(
+      ([eventName]) => eventName === 'bidResponse'
+    )?.[1] as ((bid: Record<string, unknown>) => void) | undefined;
+    expect(bidResponseListener).toBeTypeOf('function');
+
+    const renderer = apsRenderer();
+    // interpretResponse output: stashes the descriptor keyed by requestId (survives
+    // Prebid's bid normalization, which strips the custom trustedServerRenderer field).
+    auctionBidsToPrebidBids(
+      [
+        {
+          impid: 'div-aps',
+          renderer,
+          price: 1.0,
+          width: 300,
+          height: 250,
+          seat: 'aps',
+          creativeId: 'cr-aps',
+          adomain: [],
+        },
+      ],
+      [{ adUnitCode: 'div-aps', bidId: 'req-strip' }]
+    );
+
+    // Prebid delivered the bid with the custom field REMOVED — only requestId survives.
+    bidResponseListener!({
+      adapterCode: 'trustedServer',
+      bidderCode: 'aps',
+      adId: 'stripped-field-ad-id',
+      adUnitCode: 'div-aps',
+      ttl: 300,
+      requestId: 'req-strip',
+    });
+
+    const entry = (window as any).tsjs.apsPrebidRenderers['stripped-field-ad-id'];
+    expect(entry).toEqual(
+      expect.objectContaining({ adUnitCode: 'div-aps', renderer, markWinner: expect.any(Function) })
+    );
+  });
+
   it('does not register malformed or non-trusted APS renderer capabilities', () => {
     const warnSpy = vi.spyOn(log, 'warn').mockImplementation(() => {});
     installPrebidNpm();