diff --git a/src/commands/models.ts b/src/commands/models.ts
index fabd950..de5c424 100644
--- a/src/commands/models.ts
+++ b/src/commands/models.ts
@@ -344,15 +344,33 @@ function switchConfig(opts: SwitchOptions) {
     // Switch auxiliary tasks
     if (!config.auxiliary) config.auxiliary = {} as Record<string, AuxiliaryEntry>;
 
+    // Look up provider from cfg registry to get base_url & api_key
+    const registryProvider = findProviderFromRegistry(opts.provider);
+    const providerValue = registryProvider ? `custom:${registryProvider.name}` : opts.provider;
+
+    // Ensure custom_providers in config.yaml contains this provider
+    if (registryProvider) {
+      if (!config.custom_providers) config.custom_providers = [];
+      const existing = config.custom_providers.find((p) => p.name === registryProvider.name);
+      if (!existing) {
+        config.custom_providers.push(registryProvider);
+      }
+    }
+
     for (const task of opts.auxTasks) {
       if (!config.auxiliary[task]) {
         config.auxiliary[task] = { provider: "", model: "", timeout: 30 };
       }
-      config.auxiliary[task].provider = opts.provider;
+      config.auxiliary[task].provider = providerValue;
+      if (registryProvider) {
+        config.auxiliary[task].base_url = registryProvider.base_url;
+        const apiKey = getProviderApiKey(registryProvider);
+        if (apiKey) config.auxiliary[task].api_key = apiKey;
+      }
       if (opts.model) {
         config.auxiliary[task].model = opts.model;
       }
-      console.log(`  auxiliary.${task} → provider=${opts.provider}${opts.model ? ` model=${opts.model}` : ""}`);
+      console.log(`  auxiliary.${task} → provider=${providerValue}${opts.model ? ` model=${opts.model}` : ""}`);
     }
   } else {
     // Switch main provider — look up from cfg registry