diff --git a/server/src/main/java/org/elasticsearch/ingest/FieldInferenceBulkRequestPreprocessor.java b/server/src/main/java/org/elasticsearch/ingest/FieldInferenceBulkRequestPreprocessor.java
index 4e390bf92e569..21a99365255d9 100644
--- a/server/src/main/java/org/elasticsearch/ingest/FieldInferenceBulkRequestPreprocessor.java
+++ b/server/src/main/java/org/elasticsearch/ingest/FieldInferenceBulkRequestPreprocessor.java
@@ -18,15 +18,16 @@
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
 import org.elasticsearch.cluster.metadata.Metadata;
 import org.elasticsearch.cluster.service.ClusterService;
-import org.elasticsearch.index.IndexService;
+import org.elasticsearch.core.Releasable;
+import org.elasticsearch.index.Index;
 import org.elasticsearch.index.mapper.SemanticTextFieldMapper;
 import org.elasticsearch.indices.IndicesService;
 import org.elasticsearch.inference.TaskType;
 import org.elasticsearch.plugins.internal.DocumentParsingObserver;
 
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.BiConsumer;
 import java.util.function.IntConsumer;
 import java.util.function.Supplier;
@@ -65,22 +66,17 @@ protected void processIndexRequest(
     ) {
         assert indexRequest.isFieldInferenceDone() == false;
 
-        refs.acquire();
-        // Inference responses can update the fields concurrently
-        final Map<String, Object> sourceMap = new ConcurrentHashMap<>(indexRequest.sourceAsMap());
-        try (var inferenceRefs = new RefCountingRunnable(() -> onInferenceComplete(refs, indexRequest, sourceMap))) {
-            sourceMap.entrySet()
-                .stream()
-                .filter(entry -> fieldNeedsInference(indexRequest, entry.getKey(), entry.getValue()))
-                .forEach(entry -> {
-                    runInferenceForField(indexRequest, entry.getKey(), inferenceRefs, slot, sourceMap, onFailure);
-                });
-        }
-    }
+        IngestDocument ingestDocument = newIngestDocument(indexRequest);
+        List<String> fieldNames = ingestDocument.getSource().entrySet()
+            .stream()
+            .filter(entry -> fieldNeedsInference(indexRequest, entry.getKey(), entry.getValue()))
+            .map(Map.Entry::getKey)
+            .toList();
+
+        // Runs inference sequentially. This makes easier sync and removes the problem of having multiple
+        //   BulkItemResponses for a single bulk request in TransportBulkAction.unwrappingSingleItemBulkResponse
+        runInferenceForFields(indexRequest, fieldNames, refs.acquire(), slot, ingestDocument, onFailure);
 
-    private void onInferenceComplete(RefCountingRunnable refs, IndexRequest indexRequest, Map<String, Object> sourceMap) {
-        updateIndexRequestSource(indexRequest, newIngestDocument(indexRequest, sourceMap));
-        refs.close();
     }
 
     @Override
@@ -112,26 +108,50 @@ private boolean fieldNeedsInference(IndexRequest indexRequest, String fieldName,
     }
 
     private String getModelForField(IndexRequest indexRequest, String fieldName) {
-        IndexService indexService = indicesService.indexService(
-            indexNameExpressionResolver.concreteSingleIndex(clusterService.state(), indexRequest)
-        );
-        return indexService.mapperService().mappingLookup().modelForField(fieldName);
+        // Check all indices related to request have the same model id
+        String model = null;
+        try {
+            Index[] indices = indexNameExpressionResolver.concreteIndices(clusterService.state(), indexRequest);
+            for (Index index : indices) {
+                String modelForIndex = indicesService.indexService(index).mapperService().mappingLookup().modelForField(fieldName);
+                if ((modelForIndex == null)) {
+                    return null;
+                }
+                if ((model != null) && modelForIndex.equals(model) == false) {
+                    return null;
+                }
+                model = modelForIndex;
+            }
+        } catch (Exception e) {
+            // There's a problem retrieving the index
+            return null;
+        }
+        return model;
     }
 
-    private void runInferenceForField(
+    private void runInferenceForFields(
         IndexRequest indexRequest,
-        String fieldName,
-        RefCountingRunnable refs,
+        List<String> fieldNames,
+        Releasable ref,
         int position,
-        final Map<String, Object> sourceAsMap,
+        final IngestDocument ingestDocument,
         BiConsumer<Integer, Exception> onFailure
     ) {
-        final String fieldValue = (String) sourceAsMap.get(fieldName);
-        if (fieldValue == null) {
+        // We finished processing
+        if (fieldNames.isEmpty()) {
+            updateIndexRequestSource(indexRequest, ingestDocument);
+            indexRequest.isFieldInferenceDone(true);
+            ref.close();
             return;
         }
+        String fieldName = fieldNames.get(0);
+        List<String> nextFieldNames = fieldNames.subList(1, fieldNames.size());
+        final String fieldValue = ingestDocument.getFieldValue(fieldName, String.class);
+        if (fieldValue == null) {
+            // Run inference for next field
+            runInferenceForFields(indexRequest, nextFieldNames, ref, position, ingestDocument, onFailure);
+        }
 
-        refs.acquire();
         String modelForField = getModelForField(indexRequest, fieldName);
         assert modelForField != null : "Field " + fieldName + " has no model associated in mappings";
 
@@ -143,37 +163,31 @@ private void runInferenceForField(
             Map.of()
         );
 
-        final long startTimeInNanos = System.nanoTime();
-        ingestMetric.preIngest();
-        client.execute(InferenceAction.INSTANCE, inferenceRequest, ActionListener.runAfter(new ActionListener<InferenceAction.Response>() {
+        client.execute(InferenceAction.INSTANCE, inferenceRequest, new ActionListener<>() {
             @Override
             public void onResponse(InferenceAction.Response response) {
                 // Transform into two subfields, one with the actual text and other with the inference
                 Map<String, Object> newFieldValue = new HashMap<>();
                 newFieldValue.put(SemanticTextFieldMapper.TEXT_SUBFIELD_NAME, fieldValue);
                 newFieldValue.put(
-                    SemanticTextFieldMapper.SPARSE_VECTOR_SUBFIELD_NAME,
-                    response.getResult().asMap(fieldName).get(fieldName)
+                        SemanticTextFieldMapper.SPARSE_VECTOR_SUBFIELD_NAME,
+                        response.getResult().asMap(fieldName).get(fieldName)
                 );
-                sourceAsMap.put(fieldName, newFieldValue);
+                ingestDocument.setFieldValue(fieldName, newFieldValue);
+
+                // Run inference for next fields
+                runInferenceForFields(indexRequest, nextFieldNames, ref, position, ingestDocument, onFailure);
             }
 
             @Override
             public void onFailure(Exception e) {
                 // Wrap exception in an illegal argument exception, as there is a problem with the model or model config
                 onFailure.accept(
-                    position,
-                    new IllegalArgumentException("Error performing inference for field [" + fieldName + "]: " + e.getMessage(), e)
+                        position,
+                        new IllegalArgumentException("Error performing inference for field [" + fieldName + "]: " + e.getMessage(), e)
                 );
-                ingestMetric.ingestFailed();
+                ref.close();
             }
-        }, () -> {
-            // regardless of success or failure, we always stop the ingest "stopwatch" and release the ref to indicate
-            // that we're finished with this document
-            indexRequest.isFieldInferenceDone(true);
-            final long ingestTimeInNanos = System.nanoTime() - startTimeInNanos;
-            ingestMetric.postIngest(ingestTimeInNanos);
-            refs.close();
-        }));
+        });
     }
 }