diff --git a/legacy/src/llms/llm.ts b/legacy/src/llms/llm.ts
index 7eca5f0c..945aefe0 100644
--- a/legacy/src/llms/llm.ts
+++ b/legacy/src/llms/llm.ts
@@ -19,6 +19,7 @@ import {
   extractJSONObjectFromString
 } from '@/utils'
 
+// TODO: TInput should only be allowed to be an object
 export abstract class BaseLLM<
   TInput = void,
   TOutput = string,
@@ -142,6 +143,28 @@ export abstract class BaseChatModel<
     this._messages = options.messages
   }
 
+  // TODO: use polymorphic `this` type to return correct BaseLLM subclass type
+  input<U>(inputSchema: ZodType<U>): BaseChatModel<U, TOutput, TModelParams> {
+    const refinedInstance = this as unknown as BaseChatModel<
+      U,
+      TOutput,
+      TModelParams
+    >
+    refinedInstance._inputSchema = inputSchema
+    return refinedInstance
+  }
+
+  // TODO: use polymorphic `this` type to return correct BaseLLM subclass type
+  output<U>(outputSchema: ZodType<U>): BaseChatModel<TInput, U, TModelParams> {
+    const refinedInstance = this as unknown as BaseChatModel<
+      TInput,
+      U,
+      TModelParams
+    >
+    refinedInstance._outputSchema = outputSchema
+    return refinedInstance
+  }
+
   protected abstract _createChatCompletion(
     messages: types.ChatMessage[]
   ): Promise<types.BaseChatCompletionResponse<TChatCompletionResponse>>
diff --git a/legacy/test/openai.test.ts b/legacy/test/openai.test.ts
index 9863706c..6314f2a0 100644
--- a/legacy/test/openai.test.ts
+++ b/legacy/test/openai.test.ts
@@ -4,10 +4,48 @@ import sinon from 'sinon'
 import { z } from 'zod'
 
 import { OutputValidationError, TemplateValidationError } from '@/errors'
-import { OpenAIChatModel } from '@/llms/openai'
+import { BaseChatModel, OpenAIChatModel } from '@/llms'
 
 import { createTestAgenticRuntime } from './_utils'
 
+test('OpenAIChatModel ⇒ types', async (t) => {
+  const agentic = createTestAgenticRuntime()
+  const b = agentic.gpt4('test')
+  t.pass()
+
+  expectTypeOf(b).toMatchTypeOf<OpenAIChatModel<any, string>>()
+
+  expectTypeOf(
+    b.input(
+      z.object({
+        foo: z.string()
+      })
+    )
+  ).toMatchTypeOf<
+    BaseChatModel<
+      {
+        foo: string
+      },
+      string
+    >
+  >()
+
+  expectTypeOf(
+    b.output(
+      z.object({
+        bar: z.string().optional()
+      })
+    )
+  ).toMatchTypeOf<
+    BaseChatModel<
+      any,
+      {
+        bar?: string
+      }
+    >
+  >()
+})
+
 test('OpenAIChatModel ⇒ string output', async (t) => {
   t.timeout(2 * 60 * 1000)
   const agentic = createTestAgenticRuntime()
@@ -165,7 +203,7 @@ test('OpenAIChatModel ⇒ template variables', async (t) => {
   }
 })
 
-test.only('OpenAIChatModel ⇒ missing template variable', async (t) => {
+test('OpenAIChatModel ⇒ missing template variable', async (t) => {
   t.timeout(2 * 60 * 1000)
   const agentic = createTestAgenticRuntime()
 
diff --git a/legacy/test/twilio-conversation.test.ts b/legacy/test/twilio-conversation.test.ts
index f815b927..4a254fe3 100644
--- a/legacy/test/twilio-conversation.test.ts
+++ b/legacy/test/twilio-conversation.test.ts
@@ -15,7 +15,7 @@ test('TwilioConversationClient.createConversation', async (t) => {
   const conversation = await client.createConversation(friendlyName)
   t.is(conversation.friendly_name, friendlyName)
 
-  client.deleteConversation(conversation.sid)
+  await client.deleteConversation(conversation.sid)
 })
 
 test('TwilioConversationClient.addParticipant', async (t) => {
@@ -90,7 +90,7 @@ test('TwilioConversationClient.sendAndWaitForReply', async (t) => {
   await t.throwsAsync(
     async () => {
       await client.sendAndWaitForReply({
-        recipientPhoneNumber: process.env.TWILIO_TEST_PHONE_NUMBER as string,
+        recipientPhoneNumber: process.env.TWILIO_TEST_PHONE_NUMBER!,
         text: 'Please confirm by replying with "yes" or "no".',
         name: 'wait-for-reply-test',
         validate: (message) =>
@@ -122,7 +122,7 @@ test('TwilioConversationClient.sendAndWaitForReply.stopSignal', async (t) => {
     async () => {
       const controller = new AbortController()
       const promise = client.sendAndWaitForReply({
-        recipientPhoneNumber: process.env.TWILIO_TEST_PHONE_NUMBER as string,
+        recipientPhoneNumber: process.env.TWILIO_TEST_PHONE_NUMBER!,
         text: 'Please confirm by replying with "yes" or "no".',
         name: 'wait-for-reply-test',
         validate: (message) =>