diff --git a/strix/config/models.py b/strix/config/models.py
index 1f480ba7..b70192b5 100644
--- a/strix/config/models.py
+++ b/strix/config/models.py
@@ -168,6 +168,12 @@ def model_supports_adaptive_thinking(model_name: str) -> bool:
     return bool(entry and entry.get("supports_adaptive_thinking"))
 
 
+def model_supports_xhigh_effort(model_name: str) -> bool:
+    """Whether the model accepts the ``xhigh`` effort tier."""
+    entry = _model_cost_entry(model_name)
+    return bool(entry and entry.get("supports_xhigh_reasoning_effort"))
+
+
 def is_known_openai_bare_model(model_name: str) -> bool:
     import litellm
 
diff --git a/strix/core/inputs.py b/strix/core/inputs.py
index 9bdc4d9a..a736005c 100644
--- a/strix/core/inputs.py
+++ b/strix/core/inputs.py
@@ -12,6 +12,7 @@ from strix.config.models import (
     DEFAULT_MODEL_RETRY,
     model_supports_adaptive_thinking,
     model_supports_reasoning,
+    model_supports_xhigh_effort,
 )
 
 
@@ -129,11 +130,19 @@ def make_model_settings(
             # Newer Anthropic models (e.g. Claude Opus 4.8) reject the legacy
             # ``thinking.type=enabled`` shape that LiteLLM emits from
             # ``reasoning_effort``. Send the adaptive-thinking API instead.
+            # Bedrock's ``output_config.effort`` only accepts low/medium/high
+            # (plus xhigh on models that advertise it), so normalize the wider
+            # ReasoningEffort range onto that set.
+            effort = reasoning_effort
+            if effort == "minimal":
+                effort = "low"
+            elif effort == "xhigh" and not model_supports_xhigh_effort(model_name):
+                effort = "high"
             model_settings = model_settings.resolve(
                 ModelSettings(
                     extra_args={
                         "thinking": {"type": "adaptive"},
-                        "output_config": {"effort": reasoning_effort},
+                        "output_config": {"effort": effort},
                     },
                 ),
             )