diff --git a/src/Providers/OpenAI/Support/StructuredModeResolver.php b/src/Providers/OpenAI/Support/StructuredModeResolver.php
index ea77ba961..14d9abaac 100644
--- a/src/Providers/OpenAI/Support/StructuredModeResolver.php
+++ b/src/Providers/OpenAI/Support/StructuredModeResolver.php
@@ -43,6 +43,7 @@ protected static function supportsStructuredMode(string $model): bool
             'gpt-5.1',
             'gpt-5.2',
             'gpt-5.4',
+            'gpt-5.6-luna',
         ]);
     }
 
diff --git a/tests/Providers/OpenAI/StructuredModeResolverTest.php b/tests/Providers/OpenAI/StructuredModeResolverTest.php
new file mode 100644
index 000000000..786cdfaaf
--- /dev/null
+++ b/tests/Providers/OpenAI/StructuredModeResolverTest.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Providers\OpenAI;
+
+use Prism\Prism\Enums\StructuredMode;
+use Prism\Prism\Providers\OpenAI\Support\StructuredModeResolver;
+
+it('resolves GPT-5.6 Luna to strict structured mode', function (): void {
+    expect(StructuredModeResolver::forModel('gpt-5.6-luna'))
+        ->toBe(StructuredMode::Structured);
+});