diff --git a/src/ansari/config.py b/src/ansari/config.py
index 8c672a1..496cce4 100644
--- a/src/ansari/config.py
+++ b/src/ansari/config.py
@@ -195,7 +195,7 @@ def get_resource_path(filename):
     AYAH_SYSTEM_PROMPT_FILE_NAME: str = Field(default="system_msg_ayah")
     PROMPT_PATH: str = Field(default=str(get_resource_path("prompts")))
     AGENT: str = Field(default="AnsariClaude")
-    ANTHROPIC_MODEL: str = Field(default="claude-sonnet-4-20250514")
+    ANTHROPIC_MODEL: str = Field(default="claude-sonnet-4-5")
     LOGGING_LEVEL: str = Field(default="INFO")
     DEV_MODE: bool = Field(default=False)
 
diff --git a/tests/unit/test_ansari_claude_model_version.py b/tests/unit/test_ansari_claude_model_version.py
new file mode 100644
index 0000000..c333a20
--- /dev/null
+++ b/tests/unit/test_ansari_claude_model_version.py
@@ -0,0 +1,96 @@
+"""Unit tests for AnsariClaude model version verification."""
+
+import pytest
+from unittest.mock import MagicMock, patch
+
+
+@pytest.fixture
+def mock_settings():
+    """Mock settings for testing."""
+    settings = MagicMock()
+    settings.ANTHROPIC_API_KEY = MagicMock()
+    settings.ANTHROPIC_API_KEY.get_secret_value.return_value = "test-api-key"
+    settings.ANTHROPIC_MODEL = "claude-sonnet-4-5"
+    settings.KALEMAT_API_KEY = MagicMock()
+    settings.KALEMAT_API_KEY.get_secret_value.return_value = "test-kalemat-key"
+    settings.VECTARA_API_KEY = MagicMock()
+    settings.VECTARA_API_KEY.get_secret_value.return_value = "test-vectara-key"
+    settings.MAWSUAH_VECTARA_CORPUS_KEY = "test-corpus-key"
+    settings.TAFSIR_VECTARA_CORPUS_KEY = "test-tafsir-key"
+    settings.USUL_API_TOKEN = MagicMock()
+    settings.USUL_API_TOKEN.get_secret_value.return_value = "test-usul-token"
+    settings.MODEL = "test-model"
+    settings.PROMPT_PATH = "/test/prompts"
+    settings.SYSTEM_PROMPT_FILE_NAME = "system_msg_default"
+    settings.AYAH_SYSTEM_PROMPT_FILE_NAME = "system_msg_ayah"
+    settings.MAX_FAILURES = 3
+    return settings
+
+
+class TestAnsariClaudeModelVersion:
+    """Test AnsariClaude model version configuration."""
+
+    def test_model_version_is_sonnet_4_5(self, mock_settings):
+        """Test that AnsariClaude uses Sonnet 4.5 model."""
+        with patch("anthropic.Anthropic"), patch("ansari.agents.ansari.PromptMgr") as mock_prompt_mgr:
+            # Mock the prompt manager
+            mock_prompt = MagicMock()
+            mock_prompt.render.return_value = "Test system prompt"
+            mock_prompt_mgr.return_value.bind.return_value = mock_prompt
+
+            from src.ansari.agents.ansari_claude import AnsariClaude
+
+            # Initialize AnsariClaude
+            ansari = AnsariClaude(mock_settings)
+
+            # Verify the model version is Sonnet 4.5
+            assert ansari.settings.ANTHROPIC_MODEL == "claude-sonnet-4-5"
+
+    def test_model_sent_to_api(self, mock_settings):
+        """Test that the correct model version is sent to the Anthropic API."""
+        with patch("anthropic.Anthropic") as mock_anthropic, patch("ansari.agents.ansari.PromptMgr") as mock_prompt_mgr:
+            # Mock the prompt manager
+            mock_prompt = MagicMock()
+            mock_prompt.render.return_value = "Test system prompt"
+            mock_prompt_mgr.return_value.bind.return_value = mock_prompt
+
+            # Mock the Anthropic client
+            mock_client = MagicMock()
+            mock_anthropic.return_value = mock_client
+
+            # Mock the response stream
+            mock_response = MagicMock()
+            mock_response.__iter__ = MagicMock(return_value=iter([]))
+            mock_client.messages.create.return_value = mock_response
+
+            from src.ansari.agents.ansari_claude import AnsariClaude
+
+            # Initialize AnsariClaude
+            ansari = AnsariClaude(mock_settings)
+
+            # Add a message to history
+            ansari.message_history = [{"role": "user", "content": "test question"}]
+
+            # Call process_one_round to trigger API call
+            list(ansari.process_one_round())
+
+            # Verify the correct model was sent to the API
+            mock_client.messages.create.assert_called_once()
+            call_args = mock_client.messages.create.call_args
+            assert call_args[1]["model"] == "claude-sonnet-4-5"
+
+    def test_default_config_uses_sonnet_4_5(self):
+        """Test that the default configuration in Settings uses Sonnet 4.5."""
+        from src.ansari.config import Settings
+
+        # Create settings with defaults (no overrides)
+        settings = Settings(
+            OPENAI_API_KEY="test-key",
+            ANTHROPIC_API_KEY="test-key",
+            KALEMAT_API_KEY="test-key",
+            VECTARA_API_KEY="test-key",
+            QURAN_DOT_COM_API_KEY="test-key",
+        )
+
+        # Verify the default model is Sonnet 4.5
+        assert settings.ANTHROPIC_MODEL == "claude-sonnet-4-5"