diff --git a/src/main/java/com/llmproxy/service/llm/ModelVersionValidator.java b/src/main/java/com/llmproxy/service/llm/ModelVersionValidator.java
index e778a4f..4a1d1ac 100644
--- a/src/main/java/com/llmproxy/service/llm/ModelVersionValidator.java
+++ b/src/main/java/com/llmproxy/service/llm/ModelVersionValidator.java
@@ -3,9 +3,12 @@
 import com.llmproxy.model.ModelType;
 import org.springframework.stereotype.Component;
 
-import java.util.HashMap;
+import java.util.Collections;
+import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
+import java.util.HashSet;
 
 @Component
 public class ModelVersionValidator {
@@ -15,10 +18,15 @@ public class ModelVersionValidator {
     public static final String DEFAULT_CLAUDE_VERSION = "claude-3-sonnet-20240229";
     
     private final Map<ModelType, List<String>> supportedModelVersions;
+    private final Map<ModelType, Set<String>> validVersionSets;
     
     public ModelVersionValidator() {
-        supportedModelVersions = new HashMap<>();
-        supportedModelVersions.put(ModelType.OPENAI, List.of(
+        // Use EnumMap for better performance with enum keys
+        supportedModelVersions = new EnumMap<>(ModelType.class);
+        validVersionSets = new EnumMap<>(ModelType.class);
+        
+        // Define lists once and store immutable references
+        List<String> openaiVersions = List.of(
                 "gpt-4o",
                 "gpt-4o-mini",
                 "gpt-4-turbo",
@@ -26,8 +34,9 @@ public ModelVersionValidator() {
                 "gpt-4-vision-preview",
                 "gpt-3.5-turbo",
                 "gpt-3.5-turbo-16k"
-        ));
-        supportedModelVersions.put(ModelType.GEMINI, List.of(
+        );
+        
+        List<String> geminiVersions = List.of(
                 "gemini-2.5-flash-preview-04-17",
                 "gemini-2.5-pro-preview-03-25",
                 "gemini-2.0-flash",
@@ -37,8 +46,9 @@ public ModelVersionValidator() {
                 "gemini-1.5-pro",
                 "gemini-pro",
                 "gemini-pro-vision"
-        ));
-        supportedModelVersions.put(ModelType.MISTRAL, List.of(
+        );
+        
+        List<String> mistralVersions = List.of(
                 "codestral-latest",
                 "mistral-large-latest",
                 "mistral-saba-latest",
@@ -46,8 +56,9 @@ public ModelVersionValidator() {
                 "mistral-small",
                 "mistral-medium",
                 "mistral-large"
-        ));
-        supportedModelVersions.put(ModelType.CLAUDE, List.of(
+        );
+        
+        List<String> claudeVersions = List.of(
                 "claude-3-opus-20240229",
                 "claude-3-sonnet-20240229",
                 "claude-3-haiku-20240307",
@@ -56,7 +67,17 @@ public ModelVersionValidator() {
                 "claude-3-haiku",
                 "claude-2.1",
                 "claude-2.0"
-        ));
+        );
+        
+        supportedModelVersions.put(ModelType.OPENAI, openaiVersions);
+        supportedModelVersions.put(ModelType.GEMINI, geminiVersions);
+        supportedModelVersions.put(ModelType.MISTRAL, mistralVersions);
+        supportedModelVersions.put(ModelType.CLAUDE, claudeVersions);
+        
+        // Create sets for O(1) lookups instead of stream filtering
+        for (Map.Entry<ModelType, List<String>> entry : supportedModelVersions.entrySet()) {
+            validVersionSets.put(entry.getKey(), new HashSet<>(entry.getValue()));
+        }
     }
     
     public String validateModelVersion(ModelType modelType, String version) {
@@ -64,11 +85,9 @@ public String validateModelVersion(ModelType modelType, String version) {
             return getDefaultVersionForModel(modelType);
         }
         
-        List<String> validVersions = supportedModelVersions.get(modelType);
-        return validVersions.stream()
-                .filter(v -> v.equals(version))
-                .findFirst()
-                .orElse(getDefaultVersionForModel(modelType));
+        Set<String> validVersions = validVersionSets.get(modelType);
+        return validVersions != null && validVersions.contains(version) ? 
+               version : getDefaultVersionForModel(modelType);
     }
     
     private String getDefaultVersionForModel(ModelType modelType) {
@@ -81,6 +100,6 @@ private String getDefaultVersionForModel(ModelType modelType) {
     }
     
     public List<String> getSupportedVersionsForModel(ModelType modelType) {
-        return supportedModelVersions.getOrDefault(modelType, List.of());
+        return supportedModelVersions.getOrDefault(modelType, Collections.emptyList());
     }
-}
+}
\ No newline at end of file