diff --git a/kouyu_english/lib/core/ai_service.dart b/kouyu_english/lib/core/ai_service.dart
index 5a78344..1ef23b9 100644
--- a/kouyu_english/lib/core/ai_service.dart
+++ b/kouyu_english/lib/core/ai_service.dart
@@ -221,6 +221,11 @@ class AiService {
 
   static bool _isHttpUri(Uri uri) => uri.scheme == 'https' || uri.scheme == 'http';
 
+  static bool _isDeepSeek(Uri uri) {
+    final host = uri.host.toLowerCase();
+    return host == 'deepseek.com' || host.endsWith('.deepseek.com');
+  }
+
   static bool _isSuccess(http.Response response) =>
       response.statusCode >= 200 && response.statusCode < 300;
 
@@ -373,6 +378,27 @@ class AiService {
     String reasoningEffort = 'low',
   }) {
     final isResponses = uri.path.endsWith('/responses');
+    // DeepSeek thinks by default. Every request here is a short JSON answer
+    // with a small token cap, so reasoning only adds cost and can exhaust the
+    // cap before the JSON is written. Other providers may reject these
+    // DeepSeek-specific switches, so they keep the original payload.
+    if (_isDeepSeek(uri)) {
+      return isResponses
+          ? {
+              'model': model,
+              'input': messages,
+              'reasoning': {'effort': 'none'},
+              'temperature': ?temperature,
+              'max_output_tokens': ?maxTokens,
+            }
+          : {
+              'model': model,
+              'messages': messages,
+              'thinking': {'type': 'disabled'},
+              'temperature': ?temperature,
+              'max_tokens': ?maxTokens,
+            };
+    }
     if (isResponses) {
       return {
         'model': model,
diff --git a/kouyu_english/test/deepseek_thinking_test.dart b/kouyu_english/test/deepseek_thinking_test.dart
new file mode 100644
index 0000000..d1e9dcc
--- /dev/null
+++ b/kouyu_english/test/deepseek_thinking_test.dart
@@ -0,0 +1,64 @@
+import 'dart:convert';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:http/http.dart' as http;
+import 'package:http/testing.dart';
+import 'package:kouyu_english/core/ai_service.dart';
+import 'package:kouyu_english/core/models.dart';
+
+void main() {
+  const definition = '{"definition":"苹果"}';
+
+  Future<Map<String, dynamic>> captureBody(String endpoint) async {
+    AiService.instance.setFallbackApiKey('test-key');
+    Map<String, dynamic>? body;
+    final result = await http.runWithClient(
+      () => AiService.instance.temporaryDefinition(
+        provider: AiProviderType.compatible,
+        endpoint: endpoint,
+        model: 'deepseek-flash',
+        text: 'apple',
+      ),
+      () => MockClient((request) async {
+        body = jsonDecode(request.body) as Map<String, dynamic>;
+        return http.Response(
+          jsonEncode({
+            'choices': [
+              {
+                'message': {'content': definition},
+              },
+            ],
+            'output_text': definition,
+          }),
+          200,
+          headers: {'content-type': 'application/json; charset=utf-8'},
+        );
+      }),
+    );
+    expect(result, '苹果');
+    return body!;
+  }
+
+  test('DeepSeek chat completions request disables thinking', () async {
+    final body = await captureBody('https://api.deepseek.com');
+
+    expect(body['thinking'], {'type': 'disabled'});
+    expect(body.containsKey('reasoning_effort'), isFalse);
+    expect(body['max_tokens'], 200);
+  });
+
+  test('DeepSeek responses request sets reasoning effort to none', () async {
+    final body = await captureBody('https://api.deepseek.com/v1/responses');
+
+    expect(body['reasoning'], {'effort': 'none'});
+    expect(body.containsKey('reasoning_effort'), isFalse);
+    expect(body.containsKey('thinking'), isFalse);
+  });
+
+  test('other compatible endpoints keep their original payload', () async {
+    final body = await captureBody('https://example.test/v1');
+
+    expect(body.containsKey('thinking'), isFalse);
+    expect(body['reasoning_effort'], 'low');
+  });
+}