diff --git a/modules/allegroBidAdapter.js b/modules/allegroBidAdapter.js
index 67f337531b7..9fc4fe461ec 100644
--- a/modules/allegroBidAdapter.js
+++ b/modules/allegroBidAdapter.js
@@ -140,6 +140,12 @@ const converter = ortbConverter({
   request(buildRequest, imps, bidderRequest, context) {
     const request = buildRequest(imps, bidderRequest, context);
 
+    const publisherId = bidderRequest.bids.find(bid => bid.params?.publisherId)?.params.publisherId;
+    if (publisherId) {
+      request.site = request.site || {};
+      request.site['[com.allegro.dsp.site.ext]'] = { inventory: { id: publisherId } };
+    }
+
     if (request?.device?.dnt !== undefined) {
       request.device.dnt = request.device.dnt === 1;
     }
@@ -164,7 +170,6 @@ const converter = ortbConverter({
 
     return request;
   },
-
   /**
    * Post-processes each Prebid bid response, mapping Allegro DSP extension
    * fields onto the standard `meta` object so publishers can consume them.
diff --git a/modules/allegroBidAdapter.md b/modules/allegroBidAdapter.md
index 252c5427873..7fcaeb5f570 100644
--- a/modules/allegroBidAdapter.md
+++ b/modules/allegroBidAdapter.md
@@ -54,11 +54,21 @@ var adUnits = [{
     }
   },
   bids: [{
-    bidder: 'allegro'
+    bidder: 'allegro',
+    params: {
+      publisherId: 'gwp'   // publisher identifier; maps to site.[com.allegro.dsp.site.ext].inventory.id in the outgoing OpenRTB request
+    }
   }]
 }];
 ```
 
+## Bid Request Parameters
+
+| Name     | Scope    | Type   | Description                                                                                                             |
+|----------|----------|--------|-------------------------------------------------------------------------------------------------------------------------|
+| `publisherId` | optional | String | Publisher identifier. When present, the value is written to the `[com.allegro.dsp.site.ext]` proto-JSON extension key on `site` as `inventory.id` in the outgoing OpenRTB bid request, enabling publisher-scoped bid entity filtering on the server side. |
+
+
 # Features
 ## Impression Tracking
 
@@ -103,4 +113,3 @@ Example server bid response:
 - **TTL**: 360 seconds
 - **Net Revenue**: true
 - **Content Type**: text/plain
-
diff --git a/test/spec/modules/allegroBidAdapter_spec.js b/test/spec/modules/allegroBidAdapter_spec.js
index 3134850b645..d75ffcae036 100644
--- a/test/spec/modules/allegroBidAdapter_spec.js
+++ b/test/spec/modules/allegroBidAdapter_spec.js
@@ -75,7 +75,7 @@ describe('Allegro Bid Adapter', () => {
 
     it('converts extension fields by default', () => {
       sinon.stub(config, 'getConfig').callsFake((key) => undefined);
-      const bidRequests = [buildBidRequest({})];
+      const bidRequests = [buildBidRequest({ params: { publisherId: 'gwp_pb' } })];
       const ortb2 = {
         site: { ext: { siteCustom: 'val' }, publisher: { ext: { pubCustom: 'pub' } } },
         user: { ext: { userCustom: 'usr' }, data: [{ ext: { dataCustom: 'd1' } }] },
@@ -90,6 +90,7 @@ describe('Allegro Bid Adapter', () => {
 
       expect(data.site.ext).to.equal(undefined);
       expect(data.site['[com.google.doubleclick.site]'].siteCustom).to.equal('val');
+      expect(data.site['[com.allegro.dsp.site.ext]'].inventory.id).to.equal('gwp_pb');
       expect(data.site.publisher['[com.google.doubleclick.publisher]'].pubCustom).to.equal('pub');
       expect(data.user['[com.google.doubleclick.user]'].userCustom).to.equal('usr');
       expect(data.user.data[0]['[com.google.doubleclick.data]'].dataCustom).to.equal('d1');
@@ -113,6 +114,23 @@ describe('Allegro Bid Adapter', () => {
       expect(req.data.site['[com.google.doubleclick.site]']).to.equal(undefined);
     });
 
+    it('does not add the inventory extension when publisherId is absent', () => {
+      sinon.stub(config, 'getConfig').callsFake((key) => undefined);
+      const bidRequests = [buildBidRequest({})];
+      const req = spec.buildRequests(bidRequests, buildBidderRequest(bidRequests));
+      expect(req.data.site?.['[com.allegro.dsp.site.ext]']).to.equal(undefined);
+    });
+
+    it('sets inventory.id even when allegro.convertExtensionFields = false', () => {
+      sinon.stub(config, 'getConfig').callsFake((key) => {
+        if (key === 'allegro.convertExtensionFields') return false;
+        return undefined;
+      });
+      const bidRequests = [buildBidRequest({ params: { publisherId: 'gwp_pb' } })];
+      const req = spec.buildRequests(bidRequests, buildBidderRequest(bidRequests));
+      expect(req.data.site['[com.allegro.dsp.site.ext]'].inventory.id).to.equal('gwp_pb');
+    });
+
     it('converts numeric flags to booleans (topframe, secure, test) when present', () => {
       sinon.stub(config, 'getConfig').callsFake((key) => undefined);
       const bidRequests = [buildBidRequest({ mediaTypes: { banner: { sizes: [[300, 250]], topframe: 1 } }, params: { secure: 1 } })];