diff --git a/custom_components/anthropic_custom/const.py b/custom_components/anthropic_custom/const.py
index b68b00a..fdf2427 100644
--- a/custom_components/anthropic_custom/const.py
+++ b/custom_components/anthropic_custom/const.py
@@ -31,7 +31,7 @@ DEFAULT = {
     CONF_MAX_TOKENS: 3000,
     CONF_TEMPERATURE: 1.0,
     CONF_THINKING_BUDGET: 0,
-    CONF_THINKING_EFFORT: "low",
+    CONF_THINKING_EFFORT: "medium",
     CONF_WEB_SEARCH: False,
     CONF_WEB_SEARCH_USER_LOCATION: False,
     CONF_WEB_SEARCH_MAX_USES: 5,
diff --git a/custom_components/anthropic_custom/entity.py b/custom_components/anthropic_custom/entity.py
index 7ca512a..bb6abc2 100644
--- a/custom_components/anthropic_custom/entity.py
+++ b/custom_components/anthropic_custom/entity.py
@@ -694,6 +694,11 @@ class AnthropicBaseLLMEntity(Entity):
             thinking_effort = options.get(
                 CONF_THINKING_EFFORT, DEFAULT[CONF_THINKING_EFFORT]
             )
+            # Some models (e.g. *-think variants) require minimum effort of "medium"
+            _EFFORT_ORDER = ["low", "medium", "high", "max"]
+            if "think" in model and thinking_effort in _EFFORT_ORDER:
+                if _EFFORT_ORDER.index(thinking_effort) < _EFFORT_ORDER.index("medium"):
+                    thinking_effort = "medium"
             if thinking_effort != "none":
                 model_args["thinking"] = ThinkingConfigAdaptiveParam(type="adaptive")
                 model_args["output_config"] = OutputConfigParam(effort=thinking_effort)