diff --git a/modules/yieldmoBidAdapter.js b/modules/yieldmoBidAdapter.js
index f606194e132..b834bf0dc57 100644
--- a/modules/yieldmoBidAdapter.js
+++ b/modules/yieldmoBidAdapter.js
@@ -389,13 +389,36 @@ function getPageDescription() {
 }
 
 /**
- * Gets an id from the userId object if it exists
+ * EID source for each legacy `bid.userId` key this adapter reads, so those ids
+ * can be recovered from `userIdAsEids` on Prebid 10+, where the `bid.userId`
+ * object was removed (prebid/Prebid.js#13253, first shipped in 10.0.0). Without
+ * this the tdid/pubcid/cri_prebid request params silently stop being sent.
+ */
+const EID_SOURCE_BY_USER_ID = {
+  pubcid: 'pubcid.org',
+  tdid: 'adserver.org',
+  criteoId: 'criteo.com',
+};
+
+/**
+ * Gets an id previously read from the (now-removed) `bid.userId` object.
+ * Prefers the legacy object when present (pre-Prebid 10); otherwise falls back
+ * to the matching source in `userIdAsEids`.
  * @param {*} request
  * @param {*} idType
  * @returns an id if there is one, or undefined
  */
 function getId(request, idType) {
-  return (typeof deepAccess(request, 'userId') === 'object') ? request.userId[idType] : undefined;
+  const legacyUserId = deepAccess(request, 'userId');
+  if (typeof legacyUserId === 'object' && legacyUserId != null && legacyUserId[idType] != null) {
+    return legacyUserId[idType];
+  }
+  const source = EID_SOURCE_BY_USER_ID[idType];
+  if (source) {
+    const eid = (getEids(request) || []).find(e => e && e.source === source);
+    return deepAccess(eid, 'uids.0.id');
+  }
+  return undefined;
 }
 
 /**
diff --git a/test/spec/modules/yieldmoBidAdapter_spec.js b/test/spec/modules/yieldmoBidAdapter_spec.js
index 4f4454c17ae..4f30dc1f5f3 100644
--- a/test/spec/modules/yieldmoBidAdapter_spec.js
+++ b/test/spec/modules/yieldmoBidAdapter_spec.js
@@ -267,6 +267,78 @@ describe('YieldmoAdapter', function () {
         expect(buildAndGetData([criteoIdBid]).cri_prebid).to.deep.equal(criteoId);
       });
 
+      // Prebid 10+ removed the legacy bid.userId object (prebid/Prebid.js#13253),
+      // leaving only userIdAsEids. tdid/pubcid/cri_prebid must be recovered from
+      // there so they keep being sent.
+      describe('userIdAsEids fallback (Prebid 10+, no bid.userId)', function () {
+        const eidsOnlyBid = (extraEids = []) => mockBannerBid({
+          crumbs: undefined,
+          userId: undefined,
+          userIdAsEids: [
+            { source: 'pubcid.org', uids: [{ id: 'eid_pubcid', atype: 1 }] },
+            { source: 'adserver.org', uids: [{ id: 'eid_tdid', atype: 1, ext: { rtiPartner: 'TDID' } }] },
+            { source: 'criteo.com', uids: [{ id: 'eid_criteo', atype: 1 }] },
+            ...extraEids,
+          ],
+        });
+
+        it('should read tdid from userIdAsEids adserver.org', function () {
+          expect(buildAndGetData([eidsOnlyBid()]).tdid).to.equal('eid_tdid');
+        });
+
+        it('should read pubcid from userIdAsEids pubcid.org', function () {
+          expect(buildAndGetData([eidsOnlyBid()]).pubcid).to.equal('eid_pubcid');
+        });
+
+        it('should read criteoId from userIdAsEids criteo.com', function () {
+          expect(buildAndGetData([eidsOnlyBid()]).cri_prebid).to.equal('eid_criteo');
+        });
+
+        it('should prefer the legacy bid.userId object when both are present', function () {
+          const bid = eidsOnlyBid();
+          bid.userId = { tdid: 'legacy_tdid' };
+          expect(buildAndGetData([bid]).tdid).to.equal('legacy_tdid');
+        });
+
+        it('should omit an id whose source is absent from userIdAsEids', function () {
+          const bid = mockBannerBid({
+            crumbs: undefined,
+            userId: undefined,
+            userIdAsEids: [{ source: 'pubcid.org', uids: [{ id: 'eid_pubcid', atype: 1 }] }],
+          });
+          expect(buildAndGetData([bid])).to.not.have.property('tdid');
+        });
+
+        // Real getUserIdsAsEids() capture from www.yahoo.com (Prebid 9.53.2): a
+        // 13-source blob with a single adserver.org entry tagged rtiPartner TDID, a
+        // pubcid.org, no criteo, plus 11 sources we never read as flat params.
+        // Verifies flat tdid/pubcid are recovered on 10+ and every source still ships
+        // via the `eids` param.
+        it('should recover pubcid/tdid from a real Yahoo userIdAsEids blob and forward all sources', function () {
+          const yahooEids = [
+            { source: 'yahoo.com', uids: [{ id: 'ceKGMBMyiD_y9Hiy3yEezGpqPWhG9vckE9uQ9dXvzZ7YH5B3OcU3GkuAGulWrJrGMqumCS4bkIWCl_HKMsb2eQ', atype: 3 }] },
+            { source: 'liveramp.com', uids: [{ id: 'ApoINPkmDal1SZ-1eFryc322FuBMuiTIfa0n83qkZ9d4TmmF2yjDwWNFt0rOB2DBaH5YnHs', atype: 3 }] },
+            { source: 'liveintent.com', uids: [{ id: '31-AEQ3i4A7U6Q/VmkQW8HMRDb69Hc4Dmb3d9Vw5OujdEhuKayNFArmrWkjwcXZsaWltfVm1zsQVPR6lhgSdD4H6PLANZWX8wE7ctQxbQuxYgvwBQXrbQW4', atype: 3 }] },
+            { source: 'liveintent.triplelift.com', uids: [{ id: '3039651338209079102359', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'rubiconproject.com', uids: [{ id: 'MEDJJCH8-O-IKN8', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'liveintent.indexexchange.com', uids: [{ id: 'aJ-V4sAoIlYAKl2pAwiuIwAA&2037', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'openx.net', uids: [{ id: '7a105d7c-4708-4c2d-a3ba-1e795e46983e', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'pubmatic.com', uids: [{ id: '4235B560-BD45-4F77-9695-19B7846C1E31', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'liveintent.sovrn.com', uids: [{ id: 'LLFyABZHZ8flvu7cQ-Giva3O', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'liveintent.sonobi.com', uids: [{ id: '9706c68f-27f2-4424-af37-ab315995f8b0', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'liveintent.unrulymedia.com', uids: [{ id: 'RX-1927b623-5cc4-4212-b089-32380b081397-005', atype: 3, ext: { provider: 'liveintent.com' } }] },
+            { source: 'pubcid.org', uids: [{ id: '41137366-b187-4188-bd07-7e858ac15a9b', atype: 1 }] },
+            { source: 'adserver.org', uids: [{ id: '44d89fb7-c8f6-4c5d-913f-d41707bd4511', atype: 1, ext: { rtiPartner: 'TDID' } }], inserter: 'adserver.org', matcher: 'adserver.org', mm: 4 },
+          ];
+          const data = buildAndGetData([mockBannerBid({ crumbs: undefined, userId: undefined, userIdAsEids: yahooEids })]);
+          expect(data.pubcid).to.equal('41137366-b187-4188-bd07-7e858ac15a9b');
+          expect(data.tdid).to.equal('44d89fb7-c8f6-4c5d-913f-d41707bd4511');
+          expect(data).to.not.have.property('cri_prebid');
+          // every EID source is still forwarded intact via the eids param
+          expect(JSON.parse(data.eids).map(e => e.source)).to.have.members(yahooEids.map(e => e.source));
+        });
+      });
+
       it('should add gdpr information to request if available', () => {
         const gdprConsent = {
           consentString: 'BOJ/P2HOJ/P2HABABMAAAAAZ+A==',