diff --git a/agents/research-agent/src/providers.py b/agents/research-agent/src/providers.py
index 5c81c7e2..10a760cf 100644
--- a/agents/research-agent/src/providers.py
+++ b/agents/research-agent/src/providers.py
@@ -30,7 +30,7 @@ class ProviderConfig:
 
 # Default models per provider
 DEFAULT_MODELS = {
-    Provider.ANTHROPIC: "claude-sonnet-4-20250514",
+    Provider.ANTHROPIC: "claude-sonnet-5",
     Provider.GROQ: "llama-3.1-70b-versatile",
     Provider.OLLAMA: "phi3",  # Small, fast, works on most machines
 }
diff --git a/lib/constants.ts b/lib/constants.ts
index 2ada6b55..a6012d40 100644
--- a/lib/constants.ts
+++ b/lib/constants.ts
@@ -55,7 +55,7 @@ export const API_CONFIG = {
 
   // OpenRouter
   OPENROUTER_API_URL: 'https://openrouter.ai/api/v1/chat/completions',
-  OPENROUTER_DEFAULT_MODEL: 'anthropic/claude-3.5-sonnet',
+  OPENROUTER_DEFAULT_MODEL: 'anthropic/claude-sonnet-5',
 
   // Token limits
   MAX_CONTEXT_CHARS: 8000,
diff --git a/tests/__tests__/lib/llm-client.test.ts b/tests/__tests__/lib/llm-client.test.ts
index 21b15578..1fb2afc1 100644
--- a/tests/__tests__/lib/llm-client.test.ts
+++ b/tests/__tests__/lib/llm-client.test.ts
@@ -6,7 +6,7 @@ jest.mock('@/lib/constants', () => ({
     GROQ_API_URL: 'https://api.groq.com/openai/v1/chat/completions',
     GROQ_MODEL: 'llama-3.1-8b-instant',
     OPENROUTER_API_URL: 'https://openrouter.ai/api/v1/chat/completions',
-    OPENROUTER_DEFAULT_MODEL: 'anthropic/claude-3.5-sonnet',
+    OPENROUTER_DEFAULT_MODEL: 'anthropic/claude-sonnet-5',
   },
 }));
 
@@ -162,10 +162,10 @@ describe('generateLLMResponse', () => {
       expect(mockFetch).toHaveBeenCalledWith(
         'https://openrouter.ai/api/v1/chat/completions',
         expect.objectContaining({
-          body: expect.stringContaining('"model":"anthropic/claude-3.5-sonnet"'),
+          body: expect.stringContaining('"model":"anthropic/claude-sonnet-5"'),
         }),
       );
-      expect(result.model).toBe('anthropic/claude-3.5-sonnet');
+      expect(result.model).toBe('anthropic/claude-sonnet-5');
     });
 
     it('uses custom model when specified', async () => {