diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_bbq_hnsw.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_bbq_hnsw.yml
index abde3e86dd05b..19f6bf686ac73 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_bbq_hnsw.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_bbq_hnsw.yml
@@ -71,6 +71,13 @@ setup:
       indices.flush:
         index: bbq_hnsw
 
+  # For added test reliability, pending the resolution of https://github.com/elastic/elasticsearch/issues/109416.
+  - do:
+      indices.forcemerge:
+        index: bbq_hnsw
+        max_num_segments: 1
+  - do:
+      indices.refresh: {}
   - do:
       indices.forcemerge:
         index: bbq_hnsw
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_byte_quantized.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_byte_quantized.yml
index 229d705bc317c..f3091e61f7f79 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_byte_quantized.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_byte_quantized.yml
@@ -67,6 +67,13 @@ setup:
       indices.flush:
         index: hnsw_byte_quantized
 
+  # For added test reliability, pending the resolution of https://github.com/elastic/elasticsearch/issues/109416.
+  - do:
+      indices.forcemerge:
+        index: hnsw_byte_quantized
+        max_num_segments: 1
+  - do:
+      indices.refresh: {}
   - do:
       indices.forcemerge:
         index: hnsw_byte_quantized
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_half_byte_quantized.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_half_byte_quantized.yml
index 9b27aea4b1db7..a1e87d8dfa1f0 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_half_byte_quantized.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_half_byte_quantized.yml
@@ -60,6 +60,7 @@ setup:
           vector: [0.5, 111.3, -13.0, 14.8]
           another_vector: [-0.5, 11.0, 0, 12]
 
+  # For added test reliability, pending the resolution of https://github.com/elastic/elasticsearch/issues/109416.
   - do:
       indices.forcemerge:
         index: hnsw_byte_quantized
@@ -68,6 +69,11 @@ setup:
   - do:
       indices.refresh: {}
 
+  - do:
+      indices.forcemerge:
+        index: hnsw_byte_quantized
+        max_num_segments: 1
+
 ---
 "kNN search only":
   - do:
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_bbq_flat.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_bbq_flat.yml
index 2541de7023bf0..fc8cddea9d779 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_bbq_flat.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_bbq_flat.yml
@@ -70,6 +70,13 @@ setup:
       indices.flush:
         index: bbq_flat
 
+  # For added test reliability, pending the resolution of https://github.com/elastic/elasticsearch/issues/109416.
+  - do:
+      indices.forcemerge:
+        index: bbq_flat
+        max_num_segments: 1
+  - do:
+      indices.refresh: {}
   - do:
       indices.forcemerge:
         index: bbq_flat
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int8_flat.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int8_flat.yml
index 6b59b8f641ee9..e25bb4e3893a2 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int8_flat.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int8_flat.yml
@@ -57,8 +57,17 @@ setup:
           vector: [0.5, 111.3, -13.0, 14.8, -156.0]
           another_vector: [-0.5, 11.0, 0, 12, 111.0]
 
+  # For added test reliability, pending the resolution of https://github.com/elastic/elasticsearch/issues/109416.
+  - do:
+      indices.forcemerge:
+        index: int8_flat
+        max_num_segments: 1
   - do:
       indices.refresh: {}
+  - do:
+      indices.forcemerge:
+        index: int8_flat
+        max_num_segments: 1
 
 ---
 "kNN search only":