feat(core): Add support for custom aliases for model configs. (#13546)

packages/cli/src/config/settingsSchema.ts

@@ -729,6 +729,16 @@ const SETTINGS_SCHEMA = {
           'Named presets for model configs. Can be used in place of a model name and can inherit from other aliases using an `extends` property.',
         showInDialog: false,
       },
+      customAliases: {
+        type: 'object',
+        label: 'Custom Model Config Aliases',
+        category: 'Model',
+        requiresRestart: false,
+        default: {},
+        description:
+          'Custom named presets for model configs. These are merged with (and override) the built-in aliases.',
+        showInDialog: false,
+      },
       overrides: {
         type: 'array',
         label: 'Model Config Overrides',

packages/core/src/services/modelConfigService.test.ts

@@ -576,4 +576,125 @@ describe('ModelConfigService', () => {
       });
     });
   });
+
+  describe('custom aliases', () => {
+    it('should resolve a custom alias', () => {
+      const config: ModelConfigServiceConfig = {
+        aliases: {},
+        customAliases: {
+          'my-custom-alias': {
+            modelConfig: {
+              model: 'gemini-custom',
+              generateContentConfig: {
+                temperature: 0.9,
+              },
+            },
+          },
+        },
+        overrides: [],
+      };
+      const service = new ModelConfigService(config);
+      const resolved = service.getResolvedConfig({ model: 'my-custom-alias' });
+
+      expect(resolved.model).toBe('gemini-custom');
+      expect(resolved.generateContentConfig).toEqual({
+        temperature: 0.9,
+      });
+    });
+
+    it('should allow custom aliases to override built-in aliases', () => {
+      const config: ModelConfigServiceConfig = {
+        aliases: {
+          'standard-alias': {
+            modelConfig: {
+              model: 'gemini-standard',
+              generateContentConfig: {
+                temperature: 0.5,
+              },
+            },
+          },
+        },
+        customAliases: {
+          'standard-alias': {
+            modelConfig: {
+              model: 'gemini-custom-override',
+              generateContentConfig: {
+                temperature: 0.1,
+              },
+            },
+          },
+        },
+        overrides: [],
+      };
+      const service = new ModelConfigService(config);
+      const resolved = service.getResolvedConfig({ model: 'standard-alias' });
+
+      expect(resolved.model).toBe('gemini-custom-override');
+      expect(resolved.generateContentConfig).toEqual({
+        temperature: 0.1,
+      });
+    });
+  });
+
+  describe('unrecognized models', () => {
+    it('should apply overrides to unrecognized model names', () => {
+      const unregisteredModelName = 'my-unregistered-model-v1';
+      const config: ModelConfigServiceConfig = {
+        aliases: {}, // No aliases defined
+        overrides: [
+          {
+            match: { model: unregisteredModelName },
+            modelConfig: {
+              generateContentConfig: {
+                temperature: 0.01,
+              },
+            },
+          },
+        ],
+      };
+      const service = new ModelConfigService(config);
+
+      // Request the unregistered model directly
+      const resolved = service.getResolvedConfig({
+        model: unregisteredModelName,
+      });
+
+      // It should preserve the model name and apply the override
+      expect(resolved.model).toBe(unregisteredModelName);
+      expect(resolved.generateContentConfig).toEqual({
+        temperature: 0.01,
+      });
+    });
+
+    it('should apply scoped overrides to unrecognized model names', () => {
+      const unregisteredModelName = 'my-unregistered-model-v1';
+      const config: ModelConfigServiceConfig = {
+        aliases: {},
+        overrides: [
+          {
+            match: {
+              model: unregisteredModelName,
+              overrideScope: 'special-agent',
+            },
+            modelConfig: {
+              generateContentConfig: {
+                temperature: 0.99,
+              },
+            },
+          },
+        ],
+      };
+      const service = new ModelConfigService(config);
+
+      const resolved = service.getResolvedConfig({
+        model: unregisteredModelName,
+        overrideScope: 'special-agent',
+      });
+
+      expect(resolved.model).toBe(unregisteredModelName);
+      expect(resolved.generateContentConfig).toEqual({
+        temperature: 0.99,
+      });
+    });
+  });
 });

packages/core/src/services/modelConfigService.ts

@@ -43,6 +43,7 @@ export interface ModelConfigAlias {
 
 export interface ModelConfigServiceConfig {
   aliases?: Record<string, ModelConfigAlias>;
+  customAliases?: Record<string, ModelConfigAlias>;
   overrides?: ModelConfigOverride[];
 }
 
@@ -104,8 +105,12 @@ export class ModelConfigService {
     generateContentConfig: GenerateContentConfig;
   } {
     const config = this.config || {};
-    const { aliases = {}, overrides = [] } = config;
-    const allAliases = { ...aliases, ...this.runtimeAliases };
+    const { aliases = {}, customAliases = {}, overrides = [] } = config;
+    const allAliases = {
+      ...aliases,
+      ...customAliases,
+      ...this.runtimeAliases,
+    };
     let baseModel: string | undefined = context.model;
     let resolvedConfig: GenerateContentConfig = {};