diff --git a/src/LaunchDarkly/Impl/Util.php b/src/LaunchDarkly/Impl/Util.php
index f90f9876..aa4efc72 100644
--- a/src/LaunchDarkly/Impl/Util.php
+++ b/src/LaunchDarkly/Impl/Util.php
@@ -126,6 +126,9 @@ public static function eventHeaders(string $sdkKey, $applicationInfo): array
     {
         $headers = Util::defaultHeaders($sdkKey, $applicationInfo);
         $headers['X-LaunchDarkly-Event-Schema'] = EventPublisher::CURRENT_SCHEMA_VERSION;
+        // Only the presence of this header is important. We encode a string
+        // value of 'true' to ensure it isn't dropped along the way.
+        $headers['X-LaunchDarkly-Unsummarized'] = 'true';
 
         return $headers;
     }
diff --git a/src/LaunchDarkly/Subsystems/EventPublisher.php b/src/LaunchDarkly/Subsystems/EventPublisher.php
index c2ff9fc7..6062a9bf 100644
--- a/src/LaunchDarkly/Subsystems/EventPublisher.php
+++ b/src/LaunchDarkly/Subsystems/EventPublisher.php
@@ -18,7 +18,7 @@ interface EventPublisher
      * @var int
      * @ignore
      */
-    const CURRENT_SCHEMA_VERSION = 2;
+    const CURRENT_SCHEMA_VERSION = 4;
 
     /**
      * @param string $sdkKey The SDK key for your account
diff --git a/tests/Impl/Integrations/EventPublisherTest.php b/tests/Impl/Integrations/EventPublisherTest.php
index 090a2d1c..3d68f21c 100644
--- a/tests/Impl/Integrations/EventPublisherTest.php
+++ b/tests/Impl/Integrations/EventPublisherTest.php
@@ -88,6 +88,7 @@ public function testSendsCorrectBodyAndHeaders($publisher)
         $this->assertEquals('sdk-key', $headers['Authorization']);
         $this->assertEquals('PHPClient/' . LDClient::VERSION, $headers['User-Agent']);
         $this->assertEquals(EventPublisher::CURRENT_SCHEMA_VERSION, $headers['X-LaunchDarkly-Event-Schema']);
+        $this->assertArrayHasKey('X-LaunchDarkly-Unsummarized', $headers);
         $this->assertEquals('application-id/my-id application-version/my-version', $headers['X-LaunchDarkly-Tags']);
     }
 }