diff --git a/run_agent.py b/run_agent.py
index 4e9b95567..d22543f85 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -1149,6 +1149,9 @@ class AIAgent:
             except (TypeError, ValueError):
                 _config_context_length = None
 
+        # Store for reuse in switch_model (so config override persists across model switches)
+        self._config_context_length = _config_context_length
+
         # Check custom_providers per-model context_length
         if _config_context_length is None:
             _custom_providers = _agent_cfg.get("custom_providers")
@@ -1386,6 +1389,7 @@ class AIAgent:
                 base_url=self.base_url,
                 api_key=self.api_key,
                 provider=self.provider,
+                config_context_length=getattr(self, "_config_context_length", None),
             )
             self.context_compressor.model = self.model
             self.context_compressor.base_url = self.base_url
diff --git a/tests/run_agent/test_switch_model_context.py b/tests/run_agent/test_switch_model_context.py
new file mode 100644
index 000000000..8b04a7326
--- /dev/null
+++ b/tests/run_agent/test_switch_model_context.py
@@ -0,0 +1,74 @@
+"""Tests that switch_model preserves config_context_length."""
+
+from unittest.mock import MagicMock, patch
+
+from run_agent import AIAgent
+from agent.context_compressor import ContextCompressor
+
+
+def _make_agent_with_compressor(config_context_length=None) -> AIAgent:
+    """Build a minimal AIAgent with a context_compressor, skipping __init__."""
+    agent = AIAgent.__new__(AIAgent)
+
+    # Primary model settings
+    agent.model = "primary-model"
+    agent.provider = "openrouter"
+    agent.base_url = "https://openrouter.ai/api/v1"
+    agent.api_key = "sk-primary"
+    agent.api_mode = "chat_completions"
+    agent.client = MagicMock()
+    agent.quiet_mode = True
+
+    # Store config_context_length for later use in switch_model
+    agent._config_context_length = config_context_length
+
+    # Context compressor with primary model values
+    compressor = ContextCompressor(
+        model="primary-model",
+        threshold_percent=0.50,
+        base_url="https://openrouter.ai/api/v1",
+        api_key="sk-primary",
+        provider="openrouter",
+        quiet_mode=True,
+        config_context_length=config_context_length,
+    )
+    agent.context_compressor = compressor
+
+    # For switch_model
+    agent._primary_runtime = {}
+
+    return agent
+
+
+@patch("agent.model_metadata.get_model_context_length", return_value=131_072)
+def test_switch_model_preserves_config_context_length(mock_ctx_len):
+    """When switching models, config_context_length should be passed to get_model_context_length."""
+    agent = _make_agent_with_compressor(config_context_length=32_768)
+
+    assert agent.context_compressor.model == "primary-model"
+    assert agent.context_compressor.context_length == 32_768  # From config override
+
+    # Switch model
+    agent.switch_model("new-model", "openrouter", api_key="sk-new", base_url="https://openrouter.ai/api/v1")
+
+    # Verify get_model_context_length was called with config_context_length
+    mock_ctx_len.assert_called_once()
+    call_kwargs = mock_ctx_len.call_args.kwargs
+    assert call_kwargs.get("config_context_length") == 32_768
+
+    # Verify compressor was updated
+    assert agent.context_compressor.model == "new-model"
+
+
+def test_switch_model_without_config_context_length():
+    """When switching models without config override, config_context_length should be None."""
+    agent = _make_agent_with_compressor(config_context_length=None)
+
+    with patch("agent.model_metadata.get_model_context_length", return_value=128_000) as mock_ctx_len:
+        # Switch model
+        agent.switch_model("new-model", "openrouter", api_key="sk-new", base_url="https://openrouter.ai/api/v1")
+
+        # Verify get_model_context_length was called with None
+        mock_ctx_len.assert_called_once()
+        call_kwargs = mock_ctx_len.call_args.kwargs
+        assert call_kwargs.get("config_context_length") is None