diff --git a/src/routing/classify/mod.rs b/src/routing/classify/mod.rs
index 9556ca6..3cb9f67 100644
--- a/src/routing/classify/mod.rs
+++ b/src/routing/classify/mod.rs
@@ -312,14 +312,32 @@ impl Router {
             }
         }
 
-        // 3. Auto-mapping (model name transformation, after background check)
+        // 3. Auto-mapping (model name transformation, after background check).
+        //
+        // If the user has an explicit `[[models]]` entry whose name matches
+        // the incoming request model, that entry takes precedence — auto-map
+        // is a "catch-all rewrite for unconfigured models", not a forced
+        // override. Without this guard, a request for `claude-sonnet-4-6`
+        // would be rewritten to `router.default` even when the user defined
+        // a virtual `claude-sonnet-4-6` model with its own fallback chain;
+        // the chain would never run and pass-through would leak the virtual
+        // name "default-model" to the upstream provider.
         if let Some(ref mapper) = self.auto_mapper {
             if mapper.is_match(&request.model) {
-                info!(
-                    "Auto-mapped model '{}' → '{}'",
-                    request.model, self.config.router.default
-                );
-                request.model.clone_from(&self.config.router.default);
+                let has_explicit_virtual =
+                    self.config.models.iter().any(|m| m.name == request.model);
+                if has_explicit_virtual {
+                    info!(
+                        "Auto-map skipped for '{}' — explicit [[models]] entry takes precedence",
+                        request.model
+                    );
+                } else {
+                    info!(
+                        "Auto-mapped model '{}' → '{}'",
+                        request.model, self.config.router.default
+                    );
+                    request.model.clone_from(&self.config.router.default);
+                }
             }
         }
 
diff --git a/src/routing/classify/tests.rs b/src/routing/classify/tests.rs
index 75a68da..e75c6da 100644
--- a/src/routing/classify/tests.rs
+++ b/src/routing/classify/tests.rs
@@ -200,6 +200,50 @@ fn test_auto_map_custom_regex() {
     assert_eq!(decision.model_name, "default.model"); // Auto-mapped to default
 }
 
+#[test]
+fn test_auto_map_skips_explicit_virtual_model() {
+    // Regression: a request that matches the auto_map regex must NOT be
+    // rewritten to `router.default` when the user has an explicit
+    // `[[models]]` entry with the same name. Without this guard the
+    // virtual entry's fallback chain would be bypassed entirely and the
+    // virtual name would leak to a pass-through provider downstream.
+    use crate::cli::ModelConfig;
+
+    let mut config = create_test_config();
+    // Add a virtual model entry with the same name as the incoming model.
+    config.models.push(ModelConfig {
+        name: "claude-sonnet-4-6".to_string(),
+        mappings: vec![],
+        budget_usd: None,
+        strategy: Default::default(),
+        fan_out: None,
+        deprecated: None,
+    });
+    let router = Router::new(config);
+
+    let mut request = create_simple_request("Hello");
+    request.model = "claude-sonnet-4-6".to_string();
+
+    let decision = router.route(&mut request).unwrap();
+    assert_eq!(decision.route_type, RouteType::Default);
+    // Must use the explicit virtual name, NOT the auto-mapped default.
+    assert_eq!(decision.model_name, "claude-sonnet-4-6");
+}
+
+#[test]
+fn test_auto_map_still_rewrites_unmapped_claude() {
+    // Counter-test: when the user has no `[[models]]` entry for the
+    // incoming claude-* name, auto-map continues to rewrite as before.
+    let config = create_test_config();
+    let router = Router::new(config);
+
+    let mut request = create_simple_request("Hello");
+    request.model = "claude-some-unmapped-variant".to_string();
+
+    let decision = router.route(&mut request).unwrap();
+    assert_eq!(decision.model_name, "default.model");
+}
+
 #[test]
 fn test_no_auto_map_non_matching() {
     let config = create_test_config();