diff --git a/src/Responses/Responses/Output/OutputFunctionToolCall.php b/src/Responses/Responses/Output/OutputFunctionToolCall.php
index 985fa9d2..a566e43b 100644
--- a/src/Responses/Responses/Output/OutputFunctionToolCall.php
+++ b/src/Responses/Responses/Output/OutputFunctionToolCall.php
@@ -9,7 +9,7 @@
 use OpenAI\Testing\Responses\Concerns\Fakeable;
 
 /**
- * @phpstan-type OutputFunctionToolCallType array{arguments: string, call_id: string, name: string, type: 'function_call', id: string, status: 'in_progress'|'completed'|'incomplete'}
+ * @phpstan-type OutputFunctionToolCallType array{arguments: string, call_id: string, name: string, namespace?: ?string, type: 'function_call', id: string, status: 'in_progress'|'completed'|'incomplete'}
  *
  * @implements ResponseContract<OutputFunctionToolCallType>
  */
@@ -33,6 +33,7 @@ private function __construct(
         public readonly string $type,
         public readonly string $id,
         public readonly string $status,
+        public readonly ?string $namespace,
     ) {}
 
     /**
@@ -47,6 +48,7 @@ public static function from(array $attributes): self
             type: $attributes['type'],
             id: $attributes['id'],
             status: $attributes['status'],
+            namespace: $attributes['namespace'] ?? null,
         );
     }
 
@@ -59,6 +61,7 @@ public function toArray(): array
             'arguments' => $this->arguments,
             'call_id' => $this->callId,
             'name' => $this->name,
+            'namespace' => $this->namespace,
             'type' => $this->type,
             'id' => $this->id,
             'status' => $this->status,
diff --git a/tests/Fixtures/Responses.php b/tests/Fixtures/Responses.php
index 4da44a0f..7883adda 100644
--- a/tests/Fixtures/Responses.php
+++ b/tests/Fixtures/Responses.php
@@ -726,6 +726,22 @@ function outputCustomToolCall(): array
     ];
 }
 
+/**
+ * @return array<string, mixed>
+ */
+function outputFunctionToolCall(): array
+{
+    return [
+        'arguments' => '{"customer_id":"CUST-12345"}',
+        'call_id' => 'call_abc123',
+        'name' => 'list_open_orders',
+        'namespace' => 'crm',
+        'type' => 'function_call',
+        'id' => 'fc_abc123',
+        'status' => 'completed',
+    ];
+}
+
 /**
  * @return array<string, mixed>
  */
diff --git a/tests/Responses/Responses/Output/OutputFunctionToolCall.php b/tests/Responses/Responses/Output/OutputFunctionToolCall.php
new file mode 100644
index 00000000..05c3dc18
--- /dev/null
+++ b/tests/Responses/Responses/Output/OutputFunctionToolCall.php
@@ -0,0 +1,47 @@
+<?php
+
+use OpenAI\Responses\Responses\Output\OutputFunctionToolCall;
+
+test('from', function () {
+    $response = OutputFunctionToolCall::from(outputFunctionToolCall());
+
+    expect($response)
+        ->toBeInstanceOf(OutputFunctionToolCall::class)
+        ->arguments->toBe('{"customer_id":"CUST-12345"}')
+        ->callId->toBe('call_abc123')
+        ->name->toBe('list_open_orders')
+        ->namespace->toBe('crm')
+        ->type->toBe('function_call')
+        ->id->toBe('fc_abc123')
+        ->status->toBe('completed');
+});
+
+test('from without namespace', function () {
+    $attributes = outputFunctionToolCall();
+
+    unset($attributes['namespace']);
+
+    set_error_handler(static fn (int $errno, string $errstr): bool => throw new ErrorException($errstr), E_WARNING);
+
+    try {
+        $response = OutputFunctionToolCall::from($attributes);
+    } finally {
+        restore_error_handler();
+    }
+
+    expect($response->namespace)->toBeNull();
+});
+
+test('as array accessible', function () {
+    $response = OutputFunctionToolCall::from(outputFunctionToolCall());
+
+    expect($response['namespace'])->toBe('crm');
+});
+
+test('to array', function () {
+    $response = OutputFunctionToolCall::from(outputFunctionToolCall());
+
+    expect($response->toArray())
+        ->toBeArray()
+        ->toBe(outputFunctionToolCall());
+});