fix: don't set reasoning effort for non-reasoning models

src/semantic-router/pkg/extproc/reason_mode_selector.go

@@ -94,7 +94,7 @@ func getChatTemplateKwargs(model string, useReasoning bool) map[string]interface
 	}
 
 	// DeepSeek v3 family: use thinking true/false
-	if strings.Contains(lower, "deepseek") || strings.Contains(lower, "ds") {
+	if strings.Contains(lower, "deepseek") || hasDeepSeekAlias(lower) {
 		return map[string]interface{}{
 			"thinking": useReasoning,
 		}
@@ -122,47 +122,66 @@ func (r *OpenAIRouter) setReasoningModeToRequestBody(requestBody []byte, enabled
 
 	family, param := getModelFamilyAndTemplateParam(model)
 
-	// Add chat_template_kwargs for reasoning mode
-	kwargs := getChatTemplateKwargs(model, enabled)
-	if kwargs != nil {
-		requestMap["chat_template_kwargs"] = kwargs
-	} else {
-		delete(requestMap, "chat_template_kwargs")
-	}
-	// Also set Reasoning-Effort in openai request
-	// This is a hack to get the reasoning mode for openai/gpt-oss-20b to work
+	// Handle reasoning_effort first
 	originalReasoningEffort, ok := requestMap["reasoning_effort"]
 	if !ok {
 		// This seems to be the default for openai/gpt-oss models
 		originalReasoningEffort = "low"
 	}
 	var appliedEffort string
+
 	if enabled {
-		// Use configurable reasoning effort based on category
-		effort := r.getReasoningEffort(categoryName)
-		requestMap["reasoning_effort"] = effort
-		appliedEffort = effort
+		// When reasoning is enabled
+		if family == "gpt-oss" || family == "gpt" {
+			// For GPT models, use reasoning_effort
+			effort := r.getReasoningEffort(categoryName)
+			requestMap["reasoning_effort"] = effort
+			appliedEffort = effort
+			// Remove chat_template_kwargs for GPT models
+			delete(requestMap, "chat_template_kwargs")
+		} else {
+			// For other models (DeepSeek, Qwen3), use chat_template_kwargs
+			kwargs := getChatTemplateKwargs(model, enabled)
+			if kwargs != nil {
+				requestMap["chat_template_kwargs"] = kwargs
+			}
+			// Remove reasoning_effort for non-GPT models
+			delete(requestMap, "reasoning_effort")
+			appliedEffort = "N/A"
+		}
 	} else {
-		requestMap["reasoning_effort"] = originalReasoningEffort
-		if s, ok := originalReasoningEffort.(string); ok {
-			appliedEffort = s
+		// When reasoning is disabled
+		if family == "gpt-oss" {
+			// For GPT-OSS, preserve original reasoning_effort
+			requestMap["reasoning_effort"] = originalReasoningEffort
+			if s, ok := originalReasoningEffort.(string); ok {
+				appliedEffort = s
+			}
+		} else {
+			// For other models, remove reasoning_effort
+			delete(requestMap, "reasoning_effort")
+			appliedEffort = "N/A"
 		}
+		// Always remove chat_template_kwargs when reasoning is disabled
+		delete(requestMap, "chat_template_kwargs")
 	}
 
 	log.Printf("Original reasoning effort: %s", originalReasoningEffort)
-	log.Printf("Added reasoning mode (enabled: %v) and reasoning effort (%s) to request for model: %s", enabled, requestMap["reasoning_effort"], model)
+	log.Printf("Added reasoning mode (enabled: %v) and reasoning effort (%s) to request for model: %s", enabled, appliedEffort, model)
 
 	// Record metrics for template usage and effort when enabled
 	if enabled {
-		// If we applied a known template param, record its usage
-		if kwargs != nil && param != "" {
-			metrics.RecordReasoningTemplateUsage(family, param)
-		} else if kwargs == nil && param == "reasoning_effort" {
-			// For GPT/GPT-OSS, we only set reasoning_effort
+		// Record template param usage based on what we actually applied
+		if family == "gpt-oss" || family == "gpt" {
+			// For GPT models, we used reasoning_effort
+			metrics.RecordReasoningTemplateUsage(family, "reasoning_effort")
+			metrics.RecordReasoningEffortUsage(family, appliedEffort)
+		} else if param != "" {
+			// For other models (DeepSeek, Qwen3), we used chat_template_kwargs
 			metrics.RecordReasoningTemplateUsage(family, param)
+			// For non-GPT models, effort is N/A
+			metrics.RecordReasoningEffortUsage(family, appliedEffort)
 		}
-		// Record which effort level was used for this family
-		metrics.RecordReasoningEffortUsage(family, appliedEffort)
 	}
 
 	// Serialize back to JSON

src/semantic-router/pkg/extproc/reason_mode_selector_test.go

@@ -1,6 +1,11 @@
 package extproc
 
-import "testing"
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/vllm-project/semantic-router/semantic-router/pkg/config"
+)
 
 // TestGetModelFamilyAndTemplateParam verifies model-family detection and template parameter mapping
 func TestGetModelFamilyAndTemplateParam(t *testing.T) {
@@ -75,3 +80,125 @@ func TestGetModelFamilyAndTemplateParam(t *testing.T) {
 		})
 	}
 }
+
+// TestSetReasoningModeToRequestBody verifies that reasoning_effort is handled correctly for different model families
+func TestSetReasoningModeToRequestBody(t *testing.T) {
+	// Create a minimal router for testing
+	router := &OpenAIRouter{
+		Config: &config.RouterConfig{
+			DefaultReasoningEffort: "medium",
+		},
+	}
+
+	testCases := []struct {
+		name                       string
+		model                      string
+		enabled                    bool
+		initialReasoningEffort     interface{}
+		expectReasoningEffortKey   bool
+		expectedReasoningEffort    interface{}
+		expectedChatTemplateKwargs bool
+	}{
+		{
+			name:                       "GPT-OSS model with reasoning disabled - preserve reasoning_effort",
+			model:                      "gpt-oss-20b",
+			enabled:                    false,
+			initialReasoningEffort:     "low",
+			expectReasoningEffortKey:   true,
+			expectedReasoningEffort:    "low",
+			expectedChatTemplateKwargs: false,
+		},
+		{
+			name:                       "Phi4 model with reasoning disabled - remove reasoning_effort",
+			model:                      "phi4",
+			enabled:                    false,
+			initialReasoningEffort:     "low",
+			expectReasoningEffortKey:   false,
+			expectedReasoningEffort:    nil,
+			expectedChatTemplateKwargs: false,
+		},
+		{
+			name:                       "DeepSeek model with reasoning disabled - remove reasoning_effort",
+			model:                      "deepseek-v31",
+			enabled:                    false,
+			initialReasoningEffort:     "low",
+			expectReasoningEffortKey:   false,
+			expectedReasoningEffort:    nil,
+			expectedChatTemplateKwargs: false,
+		},
+		{
+			name:                       "GPT-OSS model with reasoning enabled - set reasoning_effort",
+			model:                      "gpt-oss-20b",
+			enabled:                    true,
+			initialReasoningEffort:     "low",
+			expectReasoningEffortKey:   true,
+			expectedReasoningEffort:    "medium",
+			expectedChatTemplateKwargs: false,
+		},
+		{
+			name:                       "DeepSeek model with reasoning enabled - set chat_template_kwargs",
+			model:                      "deepseek-v31",
+			enabled:                    true,
+			initialReasoningEffort:     "low",
+			expectReasoningEffortKey:   false,
+			expectedReasoningEffort:    nil,
+			expectedChatTemplateKwargs: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// Prepare initial request body
+			requestBody := map[string]interface{}{
+				"model": tc.model,
+				"messages": []map[string]string{
+					{"role": "user", "content": "test message"},
+				},
+			}
+			if tc.initialReasoningEffort != nil {
+				requestBody["reasoning_effort"] = tc.initialReasoningEffort
+			}
+
+			requestBytes, err := json.Marshal(requestBody)
+			if err != nil {
+				t.Fatalf("Failed to marshal request body: %v", err)
+			}
+
+			// Call the function under test
+			modifiedBytes, err := router.setReasoningModeToRequestBody(requestBytes, tc.enabled, "test-category")
+			if err != nil {
+				t.Fatalf("setReasoningModeToRequestBody failed: %v", err)
+			}
+
+			// Parse the modified request body
+			var modifiedRequest map[string]interface{}
+			if err := json.Unmarshal(modifiedBytes, &modifiedRequest); err != nil {
+				t.Fatalf("Failed to unmarshal modified request body: %v", err)
+			}
+
+			// Check reasoning_effort handling
+			reasoningEffort, hasReasoningEffort := modifiedRequest["reasoning_effort"]
+			if tc.expectReasoningEffortKey != hasReasoningEffort {
+				t.Fatalf("Expected reasoning_effort key presence: %v, got: %v", tc.expectReasoningEffortKey, hasReasoningEffort)
+			}
+			if tc.expectReasoningEffortKey && reasoningEffort != tc.expectedReasoningEffort {
+				t.Fatalf("Expected reasoning_effort: %v, got: %v", tc.expectedReasoningEffort, reasoningEffort)
+			}
+
+			// Check chat_template_kwargs handling
+			chatTemplateKwargs, hasChatTemplateKwargs := modifiedRequest["chat_template_kwargs"]
+			if tc.expectedChatTemplateKwargs != hasChatTemplateKwargs {
+				t.Fatalf("Expected chat_template_kwargs key presence: %v, got: %v", tc.expectedChatTemplateKwargs, hasChatTemplateKwargs)
+			}
+			if tc.expectedChatTemplateKwargs {
+				kwargs, ok := chatTemplateKwargs.(map[string]interface{})
+				if !ok {
+					t.Fatalf("Expected chat_template_kwargs to be a map")
+				}
+				if len(kwargs) == 0 {
+					t.Fatalf("Expected non-empty chat_template_kwargs")
+				}
+			}
+		})
+	}
+}