diff --git a/eng/Versions.props b/eng/Versions.props
index bcede45c76..92dd2b3fcf 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -14,7 +14,7 @@
       from appending +<commitId>, which breaks DTAAgent.
     -->
     <IncludeSourceRevisionInInformationalVersion>false</IncludeSourceRevisionInInformationalVersion>
-    <VersionPrefix>18.8.0</VersionPrefix>
+    <VersionPrefix>18.8.1</VersionPrefix>
     <PreReleaseVersionLabel>release</PreReleaseVersionLabel>
     <PreReleaseVersionIteration></PreReleaseVersionIteration>
     <!-- Allowed values: '', 'prerelease', 'release'. Set to 'release' when stabilizing. -->
diff --git a/src/Microsoft.TestPlatform.CommunicationUtilities/JsonDataSerializer.Stj.cs b/src/Microsoft.TestPlatform.CommunicationUtilities/JsonDataSerializer.Stj.cs
index 6d7b2f8dcb..f6c46815ab 100644
--- a/src/Microsoft.TestPlatform.CommunicationUtilities/JsonDataSerializer.Stj.cs
+++ b/src/Microsoft.TestPlatform.CommunicationUtilities/JsonDataSerializer.Stj.cs
@@ -8,6 +8,7 @@
 using System.Text.Encodings.Web;
 using System.Text.Json;
 using System.Text.Json.Serialization;
+using System.Text.Json.Serialization.Metadata;
 
 using Microsoft.VisualStudio.TestPlatform.CommunicationUtilities.Serialization;
 using Microsoft.VisualStudio.TestPlatform.Common.DataCollection;
@@ -74,6 +75,11 @@ static JsonDataSerializer()
         NumberHandling = JsonNumberHandling.AllowReadingFromString,
         Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
         ReferenceHandler = ReferenceHandler.IgnoreCycles,
+        // Assign an explicit reflection-based resolver. When TypeInfoResolver is null, STJ falls back to
+        // the implicit default resolver which is disabled when a test project sets
+        // JsonSerializerIsReflectionEnabledByDefault=false (that switch flows into the testhost runtimeconfig),
+        // making testhost throw while deserializing the first protocol message and the runner time out. See #16274.
+        TypeInfoResolver = new DefaultJsonTypeInfoResolver(),
     };
 
     private static partial (int version, string? messageType) ParseHeaderFromJson(string rawMessage)