diff --git a/packages/ai-assistant/src/providers/index.ts b/packages/ai-assistant/src/providers/index.ts
index 3d386bb6..49028d38 100644
--- a/packages/ai-assistant/src/providers/index.ts
+++ b/packages/ai-assistant/src/providers/index.ts
@@ -2,6 +2,7 @@ import { createOpenAI } from '@ai-sdk/openai';
 import { createAnthropic } from '@ai-sdk/anthropic';
 import { createGoogleGenerativeAI } from '@ai-sdk/google';
 import { createMoonshotAI } from '@ai-sdk/moonshotai';
+import type { LanguageModel } from 'ai';
 import { AIProvider, type AIProviderConfig } from '../types';
 
 const DEFAULT_MODELS: Record<AIProvider, string> = {
@@ -22,7 +23,7 @@ const PROVIDER_API_KEY_ENV: Record<AIProvider, string> = {
  * Creates an AI SDK LanguageModel from provider configuration.
  * Normalizes OpenAI, Anthropic, and Google into a single interface for streamText().
  */
-export function createModel(config: AIProviderConfig) {
+export function createModel(config: AIProviderConfig): LanguageModel {
   const modelName = config.model || DEFAULT_MODELS[config.provider];
 
   switch (config.provider) {
diff --git a/packages/certificates/tsconfig.json b/packages/certificates/tsconfig.json
index 9d07419f..ed2dc62f 100644
--- a/packages/certificates/tsconfig.json
+++ b/packages/certificates/tsconfig.json
@@ -6,7 +6,6 @@
     "rootDir": "./src",
     "module": "ES2022",
     "target": "ES2020",
-    "lib": ["ES2020", "DOM"],
     "moduleResolution": "bundler",
     "declaration": true,
     "declarationMap": true
diff --git a/packages/tsconfig/base.json b/packages/tsconfig/base.json
index 59098975..104aadc0 100644
--- a/packages/tsconfig/base.json
+++ b/packages/tsconfig/base.json
@@ -16,7 +16,7 @@
     "skipLibCheck": true,
     "strict": true,
     "strictNullChecks": true,
-    "lib": ["ES2016", "DOM"]
+    "lib": ["ES2020", "DOM"]
   },
   "exclude": ["node_modules"]
 }