diff --git a/sgl-router/src/protocols/responses.rs b/sgl-router/src/protocols/responses.rs
index 94c72c1ce..d7bed086c 100644
--- a/sgl-router/src/protocols/responses.rs
+++ b/sgl-router/src/protocols/responses.rs
@@ -85,6 +85,7 @@ fn default_reasoning_effort() -> Option<ReasoningEffort> {
 #[derive(Debug, Clone, Deserialize, Serialize)]
 #[serde(rename_all = "snake_case")]
 pub enum ReasoningEffort {
+    Minimal,
     Low,
     Medium,
     High,
diff --git a/sgl-router/src/routers/grpc/harmony/builder.rs b/sgl-router/src/routers/grpc/harmony/builder.rs
index 03753eead..734e3168e 100644
--- a/sgl-router/src/routers/grpc/harmony/builder.rs
+++ b/sgl-router/src/routers/grpc/harmony/builder.rs
@@ -277,6 +277,8 @@ impl HarmonyBuilder {
                 "high" => ReasoningEffort::High,
                 "medium" => ReasoningEffort::Medium,
                 "low" => ReasoningEffort::Low,
+                // Harmony does not support minimal reasoning effort
+                "minimal" => ReasoningEffort::Low,
                 _ => ReasoningEffort::Medium,
             });
 
@@ -302,6 +304,7 @@ impl HarmonyBuilder {
                 ResponsesReasoningEffort::High => ReasoningEffort::High,
                 ResponsesReasoningEffort::Medium => ReasoningEffort::Medium,
                 ResponsesReasoningEffort::Low => ReasoningEffort::Low,
+                ResponsesReasoningEffort::Minimal => ReasoningEffort::Low,
             });
 
         self.build_system_message(reasoning_effort, with_custom_tools)