diff --git a/tests/Assistants/Assistants.VectorStoresTests.cs b/tests/Assistants/Assistants.VectorStoresTests.cs
index 7d92b896..eecc3b4d 100644
--- a/tests/Assistants/Assistants.VectorStoresTests.cs
+++ b/tests/Assistants/Assistants.VectorStoresTests.cs
@@ -18,7 +18,6 @@ namespace OpenAI.Tests.VectorStores;
 
 [TestFixture(true)]
 [TestFixture(false)]
-[Parallelizable(ParallelScope.Fixtures)]
 [Category("Assistants")]
 public class VectorStoresTests : SyncAsyncTestBase
 {
diff --git a/tests/Assistants/AssistantsSmokeTests.cs b/tests/Assistants/AssistantsSmokeTests.cs
index 1f75a1b2..c6afdf97 100644
--- a/tests/Assistants/AssistantsSmokeTests.cs
+++ b/tests/Assistants/AssistantsSmokeTests.cs
@@ -7,7 +7,6 @@ namespace OpenAI.Tests.Assistants;
 
 #pragma warning disable OPENAI001
 
-[Parallelizable(ParallelScope.Fixtures)]
 [Category("Assistants")]
 [Category("Smoke")]
 public class AssistantsSmokeTests
diff --git a/tests/Assistants/AssistantsTests.cs b/tests/Assistants/AssistantsTests.cs
index 69df6ce9..b00c7bdf 100644
--- a/tests/Assistants/AssistantsTests.cs
+++ b/tests/Assistants/AssistantsTests.cs
@@ -20,7 +20,6 @@ namespace OpenAI.Tests.Assistants;
 
 [TestFixture(true)]
 [TestFixture(false)]
-[Parallelizable(ParallelScope.Fixtures)]
 [Category("Assistants")]
 public class AssistantsTests : SyncAsyncTestBase
 {
diff --git a/tests/Models/ModelsTests.cs b/tests/Models/ModelsTests.cs
index 598b8492..6966ca6e 100644
--- a/tests/Models/ModelsTests.cs
+++ b/tests/Models/ModelsTests.cs
@@ -92,7 +92,9 @@ public void DeleteModelCanParseServiceError()
             ex = Assert.Throws<ClientResultException>(() => client.DeleteModel("fake_id"));
         }
 
-        Assert.That(ex.Status, Is.EqualTo(403));
+        // If the model exists but the user doesn't own it, the service returns 403.
+        // If the model doesn't exist at all, the service returns 404.
+        Assert.That(ex.Status, Is.EqualTo(404));
     }
 
     [Test]