diff --git a/run_agent.py b/run_agent.py
index 625dc5fce2..54f18d1a1d 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -6688,6 +6688,18 @@ class AIAgent:
             options["num_ctx"] = self._ollama_num_ctx
             extra_body["options"] = options
 
+        # Ollama / custom provider: pass think=false when reasoning is disabled.
+        # Ollama does not recognise the OpenRouter-style `reasoning` extra_body
+        # field, so we use its native `think` parameter instead.
+        # This prevents thinking-capable models (Qwen3, etc.) from generating
+        # <think> blocks and producing empty-response errors when the user has
+        # set reasoning_effort: none.
+        if self.provider == "custom" and self.reasoning_config and isinstance(self.reasoning_config, dict):
+            _effort = (self.reasoning_config.get("effort") or "").strip().lower()
+            _enabled = self.reasoning_config.get("enabled", True)
+            if _effort == "none" or _enabled is False:
+                extra_body["think"] = False
+
         if self._is_qwen_portal():
             extra_body["vl_high_resolution_images"] = True
 
diff --git a/tests/run_agent/test_run_agent.py b/tests/run_agent/test_run_agent.py
index 7422f22f1f..ee67f15b05 100644
--- a/tests/run_agent/test_run_agent.py
+++ b/tests/run_agent/test_run_agent.py
@@ -928,6 +928,7 @@ class TestBuildApiKwargs:
         kwargs = agent._build_api_kwargs(messages)
         assert kwargs["max_tokens"] == 4096
 
+
     def test_qwen_portal_formats_messages_and_metadata(self, agent):
         agent.base_url = "https://portal.qwen.ai/v1"
         agent._base_url_lower = agent.base_url.lower()
@@ -983,6 +984,46 @@ class TestBuildApiKwargs:
         messages = [{"role": "system", "content": "sys"}, {"role": "user", "content": "hi"}]
         kwargs = agent._build_api_kwargs(messages)
         assert kwargs["max_tokens"] == 65536
+=======
+    def test_ollama_think_false_on_effort_none(self, agent):
+        """Custom (Ollama) provider with effort=none should inject think=false."""
+        agent.provider = "custom"
+        agent.base_url = "http://localhost:11434/v1"
+        agent._base_url_lower = agent.base_url.lower()
+        agent.reasoning_config = {"effort": "none"}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is False
+
+    def test_ollama_think_false_on_enabled_false(self, agent):
+        """Custom (Ollama) provider with enabled=false should inject think=false."""
+        agent.provider = "custom"
+        agent.base_url = "http://localhost:11434/v1"
+        agent._base_url_lower = agent.base_url.lower()
+        agent.reasoning_config = {"enabled": False}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is False
+
+    def test_ollama_no_think_param_when_reasoning_enabled(self, agent):
+        """Custom provider with reasoning enabled should NOT inject think=false."""
+        agent.provider = "custom"
+        agent.base_url = "http://localhost:11434/v1"
+        agent._base_url_lower = agent.base_url.lower()
+        agent.reasoning_config = {"enabled": True, "effort": "medium"}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is None
+
+    def test_non_custom_provider_unaffected(self, agent):
+        """OpenRouter provider with effort=none should NOT inject think=false."""
+        agent.provider = "openrouter"
+        agent.model = "qwen/qwen3.5-plus-02-15"
+        agent.reasoning_config = {"effort": "none"}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is None
+
 
 
 class TestBuildAssistantMessage: