diff --git a/qa/smoke-test-http/src/javaRestTest/java/org/elasticsearch/http/BlockedSearcherRestCancellationTestCase.java b/qa/smoke-test-http/src/javaRestTest/java/org/elasticsearch/http/BlockedSearcherRestCancellationTestCase.java
index 8803ad4af734..250fe5a3a79f 100644
--- a/qa/smoke-test-http/src/javaRestTest/java/org/elasticsearch/http/BlockedSearcherRestCancellationTestCase.java
+++ b/qa/smoke-test-http/src/javaRestTest/java/org/elasticsearch/http/BlockedSearcherRestCancellationTestCase.java
@@ -30,6 +30,7 @@ import org.elasticsearch.index.translog.TranslogStats;
 import org.elasticsearch.indices.IndicesService;
 import org.elasticsearch.plugins.EnginePlugin;
 import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.tasks.Task;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -76,6 +77,10 @@ public abstract class BlockedSearcherRestCancellationTestCase extends HttpSmokeT
         createIndex("test", Settings.builder().put(BLOCK_SEARCHER_SETTING.getKey(), true).build());
         ensureGreen("test");
 
+        assert request.getOptions().containsHeader(Task.X_OPAQUE_ID_HTTP_HEADER) == false;
+        final var opaqueId = getTestClass().getSimpleName() + "-" + getTestName() + "-" + randomUUID();
+        request.setOptions(request.getOptions().toBuilder().addHeader(Task.X_OPAQUE_ID_HTTP_HEADER, opaqueId));
+
         final List<Semaphore> searcherBlocks = new ArrayList<>();
         for (final IndicesService indicesService : internalCluster().getInstances(IndicesService.class)) {
             for (final IndexService indexService : indicesService) {
@@ -96,7 +101,8 @@ public abstract class BlockedSearcherRestCancellationTestCase extends HttpSmokeT
             }
 
             final PlainActionFuture<Response> future = new PlainActionFuture<>();
-            logger.info("--> sending request");
+            logger.info("--> sending request, opaque id={}", opaqueId);
+
             final Cancellable cancellable = getRestClient().performRequestAsync(request, wrapAsRestResponseListener(future));
 
             awaitTaskWithPrefix(actionPrefix);
@@ -108,7 +114,7 @@ public abstract class BlockedSearcherRestCancellationTestCase extends HttpSmokeT
             cancellable.cancel();
             expectThrows(CancellationException.class, future::actionGet);
 
-            assertAllCancellableTasksAreCancelled(actionPrefix);
+            assertAllCancellableTasksAreCancelled(actionPrefix, opaqueId);
         } finally {
             Releasables.close(releasables);
         }
diff --git a/server/src/main/java/org/elasticsearch/tasks/CancellableTask.java b/server/src/main/java/org/elasticsearch/tasks/CancellableTask.java
index 8a0aa2033a30..8a385617bee8 100644
--- a/server/src/main/java/org/elasticsearch/tasks/CancellableTask.java
+++ b/server/src/main/java/org/elasticsearch/tasks/CancellableTask.java
@@ -109,6 +109,11 @@ public class CancellableTask extends Task {
         return true;
     }
 
+    @Override
+    public String toString() {
+        return "CancellableTask{" + super.toString() + ", reason='" + reason + '\'' + ", isCancelled=" + isCancelled + '}';
+    }
+
     private TaskCancelledException getTaskCancelledException() {
         assert Thread.holdsLock(this);
         assert isCancelled;
diff --git a/server/src/main/java/org/elasticsearch/tasks/Task.java b/server/src/main/java/org/elasticsearch/tasks/Task.java
index 83ee08574df4..46eb59c3a8cd 100644
--- a/server/src/main/java/org/elasticsearch/tasks/Task.java
+++ b/server/src/main/java/org/elasticsearch/tasks/Task.java
@@ -225,6 +225,8 @@ public class Task implements Traceable {
             + parentTask
             + ", startTime="
             + startTime
+            + ", headers="
+            + headers
             + ", startTimeNanos="
             + startTimeNanos
             + '}';
diff --git a/test/framework/src/main/java/org/elasticsearch/test/TaskAssertions.java b/test/framework/src/main/java/org/elasticsearch/test/TaskAssertions.java
index b4ecc36fc5b9..d0862c91537c 100644
--- a/test/framework/src/main/java/org/elasticsearch/test/TaskAssertions.java
+++ b/test/framework/src/main/java/org/elasticsearch/test/TaskAssertions.java
@@ -10,16 +10,19 @@ package org.elasticsearch.test;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.elasticsearch.core.Nullable;
 import org.elasticsearch.tasks.CancellableTask;
 import org.elasticsearch.tasks.Task;
 import org.elasticsearch.tasks.TaskInfo;
-import org.elasticsearch.tasks.TaskManager;
 import org.elasticsearch.transport.TransportService;
 
+import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 
+import static junit.framework.TestCase.assertFalse;
 import static junit.framework.TestCase.assertTrue;
 import static junit.framework.TestCase.fail;
 import static org.elasticsearch.test.ESIntegTestCase.client;
@@ -59,30 +62,28 @@ public class TaskAssertions {
         });
     }
 
-    public static void assertAllCancellableTasksAreCancelled(String actionPrefix) throws Exception {
+    public static void assertAllCancellableTasksAreCancelled(String actionPrefix, @Nullable String opaqueId) throws Exception {
         logger.info("--> checking that all tasks with prefix {} are marked as cancelled", actionPrefix);
 
         assertBusy(() -> {
-            boolean foundTask = false;
+            var tasks = new ArrayList<CancellableTask>();
             for (TransportService transportService : internalCluster().getInstances(TransportService.class)) {
-                final TaskManager taskManager = transportService.getTaskManager();
+                var taskManager = transportService.getTaskManager();
                 assertTrue(taskManager.assertCancellableTaskConsistency());
-                for (CancellableTask cancellableTask : taskManager.getCancellableTasks().values()) {
-                    if (cancellableTask.getAction().startsWith(actionPrefix)) {
-                        logger.trace("--> found task with prefix [{}]: [{}]", actionPrefix, cancellableTask);
-                        foundTask = true;
-                        assertTrue(
-                            "task " + cancellableTask.getId() + "/" + cancellableTask.getAction() + " not cancelled",
-                            cancellableTask.isCancelled()
-                        );
-                        logger.trace("--> Task with prefix [{}] is marked as cancelled: [{}]", actionPrefix, cancellableTask);
-                    }
-                }
+                taskManager.getCancellableTasks().values().stream().filter(t -> t.getAction().startsWith(actionPrefix)).forEach(tasks::add);
             }
-            assertTrue("found no cancellable tasks", foundTask);
+            assertFalse("no tasks found for action: " + actionPrefix, tasks.isEmpty());
+            assertTrue(
+                tasks.toString(),
+                tasks.stream().allMatch(t -> t.isCancelled() && Objects.equals(t.getHeader(Task.X_OPAQUE_ID_HTTP_HEADER), opaqueId))
+            );
         }, 30, TimeUnit.SECONDS);
     }
 
+    public static void assertAllCancellableTasksAreCancelled(String actionPrefix) throws Exception {
+        assertAllCancellableTasksAreCancelled(actionPrefix, null);
+    }
+
     public static void assertAllTasksHaveFinished(String actionPrefix) throws Exception {
         logger.info("--> checking that all tasks with prefix {} have finished", actionPrefix);
         assertBusy(() -> {