diff --git a/plugins/model-providers/custom/__init__.py b/plugins/model-providers/custom/__init__.py
index e893be95b279..573057e92c6b 100644
--- a/plugins/model-providers/custom/__init__.py
+++ b/plugins/model-providers/custom/__init__.py
@@ -30,12 +30,19 @@ def build_api_kwargs_extras(
             options["num_ctx"] = ollama_num_ctx
             extra_body["options"] = options
 
-        # Disable thinking when reasoning is turned off
+        # Reasoning / thinking support for custom providers (vLLM, Ollama, etc.)
         if reasoning_config and isinstance(reasoning_config, dict):
             _effort = (reasoning_config.get("effort") or "").strip().lower()
             _enabled = reasoning_config.get("enabled", True)
             if _effort == "none" or _enabled is False:
                 extra_body["think"] = False
+            else:
+                # Pass through thinking enabled — vLLM/Ollama use this to
+                # enable chain-of-thought reasoning on compatible models.
+                extra_body["think"] = True
+                # Pass through effort level if specified
+                if _effort and _effort not in ("none", ""):
+                    extra_body["reasoning_effort"] = _effort
 
         return extra_body, {}
 
diff --git a/run_agent.py b/run_agent.py
index bca815da3c69..0a1eaed46d22 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -4989,6 +4989,11 @@ def _supports_reasoning_extra_body(self) -> bool:
             opts = self._lmstudio_reasoning_options_cached()
             # "off-only" (or absent) means no real reasoning capability.
             return any(opt and opt != "off" for opt in opts)
+        # Custom/vLLM/Ollama providers: pass through reasoning if user
+        # explicitly configured it.  The CustomProfile.build_api_kwargs_extras()
+        # handles the wire format (think=True/False + reasoning_effort).
+        if (self.provider or "").strip().lower() in ("custom", "ollama", "vllm", "local"):
+            return True
         if "openrouter" not in self._base_url_lower:
             return False
         if "api.mistral.ai" in self._base_url_lower: