diff --git a/backend/utils/constants.py b/backend/utils/constants.py
index 4a0ac589..b99c39e2 100644
--- a/backend/utils/constants.py
+++ b/backend/utils/constants.py
@@ -36,15 +36,33 @@ MODELS = {
         "tier_availability": ["free", "paid"]
     },
     
-    # Paid tier only models
+    # Additional free tier models
     "openrouter/deepseek/deepseek-chat-v3-0324": {
         "aliases": ["deepseek/deepseek-chat-v3-0324"],
         "pricing": {
             "input_cost_per_million_tokens": 0.38,
             "output_cost_per_million_tokens": 0.89
         },
-        "tier_availability": ["paid"]
+        "tier_availability": ["free", "paid"]
     },
+    "openrouter/moonshotai/kimi-k2": {
+        "aliases": ["moonshotai/kimi-k2"],
+        "pricing": {
+            "input_cost_per_million_tokens": 1.00,
+            "output_cost_per_million_tokens": 3.00
+        },
+        "tier_availability": ["free", "paid"]
+    },
+    "xai/grok-4": {
+        "aliases": ["grok-4"],
+        "pricing": {
+            "input_cost_per_million_tokens": 5.00,
+            "output_cost_per_million_tokens": 15.00
+        },
+        "tier_availability": ["free", "paid"]
+    },
+    
+    # Paid tier only models
     "openrouter/google/gemini-2.5-pro": {
         "aliases": ["google/gemini-2.5-pro"],
         "pricing": {
diff --git a/frontend/src/components/thread/chat-input/_use-model-selection.ts b/frontend/src/components/thread/chat-input/_use-model-selection.ts
index 2e9788c4..50dfbe2c 100644
--- a/frontend/src/components/thread/chat-input/_use-model-selection.ts
+++ b/frontend/src/components/thread/chat-input/_use-model-selection.ts
@@ -51,7 +51,7 @@ export const MODELS = {
     lowQuality: false
   },
 
-  // All models now available in free tier
+  // Premium/Paid tier models (require subscription) - except specific free models
   'moonshotai/kimi-k2': { 
     tier: 'free', 
     priority: 99,
@@ -65,37 +65,37 @@ export const MODELS = {
     lowQuality: false
   },
   'sonnet-3.7': { 
-    tier: 'free', 
+    tier: 'premium', 
     priority: 97, 
     recommended: false,
     lowQuality: false
   },
   'google/gemini-2.5-pro': { 
-    tier: 'free', 
+    tier: 'premium', 
     priority: 96,
     recommended: false,
     lowQuality: false
   },
   'gpt-4.1': { 
-    tier: 'free', 
+    tier: 'premium', 
     priority: 96,
     recommended: false,
     lowQuality: false
   },
   'sonnet-3.5': { 
-    tier: 'free', 
+    tier: 'premium', 
     priority: 90,
     recommended: false,
     lowQuality: false
   },
   'gpt-4o': { 
-    tier: 'free', 
+    tier: 'premium', 
     priority: 88,
     recommended: false,
     lowQuality: false
   },
   'gemini-2.5-flash:thinking': { 
-    tier: 'free', 
+    tier: 'premium', 
     priority: 84,
     recommended: false,
     lowQuality: false