diff --git a/modules/33acrossBidAdapter.js b/modules/33acrossBidAdapter.js
index 0e9beb22013..d8a32d75afc 100644
--- a/modules/33acrossBidAdapter.js
+++ b/modules/33acrossBidAdapter.js
@@ -36,6 +36,7 @@ const VIDEO_ORTB_PARAMS = [
   'minduration',
   'maxduration',
   'placement',
+  'plcmt',
   'protocols',
   'startdelay',
   'skip',
@@ -140,10 +141,10 @@ function _validateVideo(bid) {
   }
 
   // If placement if defined, it must be a number
-  if (
-    typeof videoParams.placement !== 'undefined' &&
-    typeof videoParams.placement !== 'number'
-  ) {
+  if ([ videoParams.placement, videoParams.plcmt ].some(value => (
+    typeof value !== 'undefined' &&
+    typeof value !== 'number'
+  ))) {
     return false;
   }
 
@@ -490,12 +491,27 @@ function _buildVideoORTB(bidRequest) {
 
   // Placement Inference Rules:
   // - If no placement is defined then default to 2 (In Banner)
+  // - If the old deprecated field is defined, use its value for the recent placement field
   // - If product is instream (for instream context) then override placement to 1
-  video.placement = video.placement || 2;
+
+  const calculatePlacementValue = () => {
+    const IN_BANNER_PLACEMENT_VALUE = 2;
+
+    if (video.placement) {
+      logWarn('[33Across Adapter] The ORTB field `placement` is deprecated, please use `plcmt` instead');
+
+      return video.placement;
+    }
+
+    return IN_BANNER_PLACEMENT_VALUE;
+  }
+
+  video.plcmt ??= calculatePlacementValue();
 
   if (product === PRODUCT.INSTREAM) {
     video.startdelay = video.startdelay || 0;
-    video.placement = 1;
+    video.plcmt = 1;
+    video.placement &&= 1;
   }
 
   // bidfloors
diff --git a/test/spec/modules/33acrossBidAdapter_spec.js b/test/spec/modules/33acrossBidAdapter_spec.js
index 9cc038428bc..936e7cee074 100644
--- a/test/spec/modules/33acrossBidAdapter_spec.js
+++ b/test/spec/modules/33acrossBidAdapter_spec.js
@@ -121,7 +121,7 @@ describe('33acrossBidAdapter:', function () {
           video: {
             w: 300,
             h: 250,
-            placement: 2,
+            plcmt: 2,
             ...params
           }
         });
@@ -733,6 +733,11 @@ describe('33acrossBidAdapter:', function () {
           'foo'
         ];
 
+        invalidPlacement.forEach((placement) => {
+          this.bid.mediaTypes.video.plcmt = placement;
+          expect(spec.isBidRequestValid(this.bid)).to.be.false;
+        });
+
         invalidPlacement.forEach((placement) => {
           this.bid.mediaTypes.video.placement = placement;
           expect(spec.isBidRequestValid(this.bid)).to.be.false;
@@ -1520,89 +1525,171 @@ describe('33acrossBidAdapter:', function () {
       });
     });
 
-    context('when mediaType has video only and context is instream', function() {
-      it('builds instream request with default params', function() {
-        const bidRequests = (
-          new BidRequestsBuilder()
-            .withVideo({context: 'instream'})
-            .build()
-        );
+    context('when mediaType has video only', function() {
+      context('and context is instream', function() {
+        it('builds instream request with default params', function() {
+          const bidRequests = (
+            new BidRequestsBuilder()
+              .withVideo({context: 'instream'})
+              .build()
+          );
 
-        const ttxRequest = new TtxRequestBuilder()
-          .withVideo()
-          .withProduct('instream')
-          .build();
+          const ttxRequest = new TtxRequestBuilder()
+            .withVideo()
+            .withProduct('instream')
+            .build();
 
-        ttxRequest.imp[0].video.placement = 1;
-        ttxRequest.imp[0].video.startdelay = 0;
+          ttxRequest.imp[0].video.plcmt = 1;
+          ttxRequest.imp[0].video.startdelay = 0;
 
-        const serverRequest = new ServerRequestBuilder()
-          .withData(ttxRequest)
-          .build();
-        const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+          const serverRequest = new ServerRequestBuilder()
+            .withData(ttxRequest)
+            .build();
+          const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
 
-        validateBuiltServerRequest(builtServerRequest, serverRequest);
-      });
+          validateBuiltServerRequest(builtServerRequest, serverRequest);
+        });
 
-      it('builds instream request with params passed', function() {
-        const bidRequests = (
-          new BidRequestsBuilder()
-            .withVideo({context: 'instream', startdelay: -2})
-            .build()
-        );
+        it('builds instream request with params passed', function() {
+          const bidRequests = (
+            new BidRequestsBuilder()
+              .withVideo({context: 'instream', startdelay: -2})
+              .build()
+          );
 
-        const ttxRequest = new TtxRequestBuilder()
-          .withVideo({startdelay: -2, placement: 1})
-          .withProduct('instream')
-          .build();
+          const ttxRequest = new TtxRequestBuilder()
+            .withVideo({startdelay: -2, plcmt: 1})
+            .withProduct('instream')
+            .build();
 
-        const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+          const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
 
-        expect(JSON.parse(builtServerRequest.data)).to.deep.equal(ttxRequest);
-      });
-    });
+          expect(JSON.parse(builtServerRequest.data)).to.deep.equal(ttxRequest);
+        });
 
-    context('when mediaType has video only and context is outstream', function() {
-      it('builds siab request with video only with default params', function() {
-        const bidRequests = (
-          new BidRequestsBuilder()
-            .withVideo({context: 'outstream'})
-            .build()
-        );
+        it('overrides the placement value', function() {
+          const bidRequests = (
+            new BidRequestsBuilder()
+              .withVideo({
+                plcmt: 2, // Incorrect placement value for an instream video
+                placement: 2, // Placement specified in the DEPRECATED field.
+                context: 'instream'
+              })
+              .build()
+          );
 
-        const ttxRequest = new TtxRequestBuilder()
-          .withVideo()
-          .withProduct('siab')
-          .build();
+          const ttxRequest = new TtxRequestBuilder()
+            .withVideo()
+            .withProduct('instream')
+            .build();
 
-        ttxRequest.imp[0].video.placement = 2;
+          ttxRequest.imp[0].video.plcmt = 1;
+          ttxRequest.imp[0].video.placement = 1;
+          ttxRequest.imp[0].video.startdelay = 0;
 
-        const serverRequest = new ServerRequestBuilder()
-          .withData(ttxRequest)
-          .build();
-        const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+          const serverRequest = new ServerRequestBuilder()
+            .withData(ttxRequest)
+            .build();
+          const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
 
-        validateBuiltServerRequest(builtServerRequest, serverRequest);
+          expect(JSON.parse(builtServerRequest.data)).to.deep.equal(ttxRequest);
+        });
+
+        context('when the placement is still specified in the DEPRECATED `placement` field', function() {
+          it('overwrites its value and sets it in the recent `plcmt` field as well', function() {
+            const bidRequests = (
+              new BidRequestsBuilder()
+                .withVideo({
+                  placement: 2, // Incorrect placement for an instream video
+                  context: 'instream'
+                })
+                .build()
+            );
+
+            const ttxRequest = new TtxRequestBuilder()
+              .withVideo()
+              .withProduct('instream')
+              .build();
+
+            ttxRequest.imp[0].video.plcmt = 1;
+            ttxRequest.imp[0].video.placement = 1;
+            ttxRequest.imp[0].video.startdelay = 0;
+
+            const serverRequest = new ServerRequestBuilder()
+              .withData(ttxRequest)
+              .build();
+            const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+
+            expect(JSON.parse(builtServerRequest.data)).to.deep.equal(ttxRequest);
+          });
+        });
       });
 
-      it('builds siab request with video params passed', function() {
-        const bidRequests = (
-          new BidRequestsBuilder()
-            .withVideo({context: 'outstream', placement: 3, playbackmethod: [2]})
-            .build()
-        );
+      context('and context is outstream', function() {
+        it('builds siab request with video only with default params', function() {
+          const bidRequests = (
+            new BidRequestsBuilder()
+              .withVideo({context: 'outstream'})
+              .build()
+          );
 
-        const ttxRequest = new TtxRequestBuilder()
-          .withVideo({placement: 3, playbackmethod: [2]})
-          .withProduct('siab')
-          .build();
+          const ttxRequest = new TtxRequestBuilder()
+            .withVideo()
+            .withProduct('siab')
+            .build();
 
-        const serverRequest = new ServerRequestBuilder()
-          .withData(ttxRequest)
-          .build();
-        const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+          // No placement specified, final value should default to 2.
+          ttxRequest.imp[0].video.plcmt = 2;
 
-        validateBuiltServerRequest(builtServerRequest, serverRequest);
+          const serverRequest = new ServerRequestBuilder()
+            .withData(ttxRequest)
+            .build();
+          const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+
+          validateBuiltServerRequest(builtServerRequest, serverRequest);
+        });
+
+        it('builds siab request with video params passed', function() {
+          const bidRequests = (
+            new BidRequestsBuilder()
+              .withVideo({context: 'outstream', plcmt: 3, playbackmethod: [2]})
+              .build()
+          );
+
+          const ttxRequest = new TtxRequestBuilder()
+            .withVideo({plcmt: 3, playbackmethod: [2]})
+            .withProduct('siab')
+            .build();
+
+          const serverRequest = new ServerRequestBuilder()
+            .withData(ttxRequest)
+            .build();
+          const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+
+          validateBuiltServerRequest(builtServerRequest, serverRequest);
+        });
+
+        context('and the placement is specified in the DEPRECATED `placement` field', function() {
+          it('sets the recent `plcmt` field', function() {
+            const bidRequests = (
+              new BidRequestsBuilder()
+                .withVideo({context: 'outstream', placement: 3, playbackmethod: [2]})
+                .build()
+            );
+
+            const ttxRequest = new TtxRequestBuilder()
+              .withVideo({plcmt: 3, placement: 3, playbackmethod: [2]})
+              .withProduct('siab')
+              .build();
+
+            const serverRequest = new ServerRequestBuilder()
+              .withData(ttxRequest)
+              .build();
+            const [ builtServerRequest ] = spec.buildRequests(bidRequests, bidderRequest);
+
+            validateBuiltServerRequest(builtServerRequest, serverRequest);
+          });
+        });
       });
     });
 
@@ -1686,7 +1773,7 @@ describe('33acrossBidAdapter:', function () {
           .withProduct('siab')
           .build();
 
-        ttxRequest.imp[0].video.placement = 2;
+        ttxRequest.imp[0].video.plcmt = 2;
 
         const serverRequest = new ServerRequestBuilder()
           .withData(ttxRequest)