diff --git a/Tests/AsobiCore.NET/Asobi.Core.Tests.csproj b/Tests/AsobiCore.NET/Asobi.Core.Tests.csproj
index b32bcd5..f155ca0 100644
--- a/Tests/AsobiCore.NET/Asobi.Core.Tests.csproj
+++ b/Tests/AsobiCore.NET/Asobi.Core.Tests.csproj
@@ -19,6 +19,7 @@
 
   <ItemGroup>
     <Compile Include="..\..\Runtime\WebSocket\AsobiDispatcher.cs" Link="Source\AsobiDispatcher.cs" />
+    <Compile Include="..\..\Runtime\Models\AuthModels.cs" Link="Source\AuthModels.cs" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/Tests/AsobiCore.NET/AuthModelsTests.cs b/Tests/AsobiCore.NET/AuthModelsTests.cs
new file mode 100644
index 0000000..fac8ee0
--- /dev/null
+++ b/Tests/AsobiCore.NET/AuthModelsTests.cs
@@ -0,0 +1,81 @@
+using System.Text.Json;
+using NUnit.Framework;
+
+namespace Asobi.Tests
+{
+    /// <summary>
+    /// License-free wire-contract tests for the guest auth models. Runs in
+    /// the .NET test project (no Unity license) so the field names the
+    /// backend sees are pinned in CI even when the Unity EditMode/PlayMode
+    /// jobs are skipped.
+    ///
+    /// At runtime the SDK serializes with UnityEngine.JsonUtility, which maps
+    /// public fields to their literal names. System.Text.Json with
+    /// IncludeFields reproduces that name mapping for these flat POCOs, so a
+    /// field rename here fails the build the same way it would break the wire.
+    /// </summary>
+    public class AuthModelsTests
+    {
+        static readonly JsonSerializerOptions Opts = new() { IncludeFields = true };
+
+        [Test]
+        public void GuestRequestSerializesDeviceFields()
+        {
+            var json = JsonSerializer.Serialize(
+                new GuestRequest { device_id = "dev-1", device_secret = "c2VjcmV0" }, Opts);
+
+            Assert.That(json, Does.Contain("\"device_id\":\"dev-1\""));
+            Assert.That(json, Does.Contain("\"device_secret\":\"c2VjcmV0\""));
+        }
+
+        [Test]
+        public void GuestUpgradeRequestSerializesCredentials()
+        {
+            var json = JsonSerializer.Serialize(
+                new GuestUpgradeRequest { username = "player1", password = "secret123" }, Opts);
+
+            Assert.That(json, Does.Contain("\"username\":\"player1\""));
+            Assert.That(json, Does.Contain("\"password\":\"secret123\""));
+        }
+
+        [Test]
+        public void AuthResponseParsesGuestCreation()
+        {
+            var raw = "{\"player_id\":\"p1\",\"access_token\":\"a\",\"refresh_token\":\"r\","
+                + "\"username\":\"guest_p1\",\"created\":true,\"guest\":true}";
+
+            var resp = JsonSerializer.Deserialize<AuthResponse>(raw, Opts);
+
+            Assert.That(resp.player_id, Is.EqualTo("p1"));
+            Assert.That(resp.access_token, Is.EqualTo("a"));
+            Assert.That(resp.refresh_token, Is.EqualTo("r"));
+            Assert.That(resp.created, Is.True);
+            Assert.That(resp.guest, Is.True);
+            Assert.That(resp.upgraded, Is.False);
+        }
+
+        [Test]
+        public void AuthResponseParsesGuestResume()
+        {
+            var raw = "{\"player_id\":\"p1\",\"access_token\":\"a2\",\"refresh_token\":\"r2\","
+                + "\"username\":\"guest_p1\",\"guest\":true}";
+
+            var resp = JsonSerializer.Deserialize<AuthResponse>(raw, Opts);
+
+            Assert.That(resp.guest, Is.True);
+            Assert.That(resp.created, Is.False);
+        }
+
+        [Test]
+        public void AuthResponseParsesUpgrade()
+        {
+            var raw = "{\"player_id\":\"p1\",\"access_token\":\"a3\",\"refresh_token\":\"r3\","
+                + "\"username\":\"player1\",\"upgraded\":true}";
+
+            var resp = JsonSerializer.Deserialize<AuthResponse>(raw, Opts);
+
+            Assert.That(resp.upgraded, Is.True);
+            Assert.That(resp.username, Is.EqualTo("player1"));
+        }
+    }
+}
diff --git a/Tests/AsobiCore.NET/AuthModelsTests.cs.meta b/Tests/AsobiCore.NET/AuthModelsTests.cs.meta
new file mode 100644
index 0000000..19969f3
--- /dev/null
+++ b/Tests/AsobiCore.NET/AuthModelsTests.cs.meta
@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: effed79ca1b34fe6a60e3a87d82ba7c5
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData:
+  assetBundleName:
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