diff --git a/src/request/transformer.ts b/src/request/transformer.ts
index 409456e..d867ddc 100644
--- a/src/request/transformer.ts
+++ b/src/request/transformer.ts
@@ -1,6 +1,16 @@
-import { ChatCompletionRequest, ResponsesRequest, InputItem, Message, Content } from "../types.js";
+import {
+  ChatCompletionRequest,
+  ResponsesRequest,
+  InputItem,
+  Message,
+  Content,
+} from "../types.js";
 import { getNormalizedModel } from "./model-map.js";
-import { getReasoningConfig, getTextVerbosity, getIncludeFields } from "./reasoning.js";
+import {
+  getReasoningConfig,
+  getTextVerbosity,
+  getIncludeFields,
+} from "./reasoning.js";
 import { getCodexInstructions } from "../prompts/index.js";
 import { logDebug, logWarn } from "../logger.js";
 
@@ -8,12 +18,14 @@ export function messagesToInput(messages: Message[]): InputItem[] {
   return messages.map((msg) => {
     const content: Content[] = [];
 
+    const contentType = msg.role === "assistant" ? "output_text" : "input_text";
+
     if (typeof msg.content === "string") {
-      content.push({ type: "input_text", text: msg.content });
+      content.push({ type: contentType, text: msg.content });
     } else if (Array.isArray(msg.content)) {
       for (const item of msg.content) {
         if (item.type === "text") {
-          content.push({ type: "input_text", text: item.text || "" });
+          content.push({ type: contentType, text: item.text || "" });
         } else if (item.type === "image_url") {
           content.push({ type: "input_image", image_url: item.image_url });
         } else {
@@ -30,7 +42,9 @@ export function messagesToInput(messages: Message[]): InputItem[] {
   });
 }
 
-export function filterInput(input: InputItem[] | undefined): InputItem[] | undefined {
+export function filterInput(
+  input: InputItem[] | undefined,
+): InputItem[] | undefined {
   if (!Array.isArray(input)) {
     return input;
   }
@@ -58,7 +72,10 @@ export async function transformChatCompletionRequest(
 ): Promise<ResponsesRequest> {
   const normalizedModel = getNormalizedModel(request.model) || request.model;
 
-  logDebug(null, `Transforming chat completion request: model=${request.model} -> ${normalizedModel}`);
+  logDebug(
+    null,
+    `Transforming chat completion request: model=${request.model} -> ${normalizedModel}`,
+  );
 
   const codexInstructions = await getCodexInstructions(normalizedModel);
   const reasoningConfig = getReasoningConfig(normalizedModel);
@@ -101,7 +118,10 @@ export async function transformResponsesRequest(
 ): Promise<ResponsesRequest> {
   const normalizedModel = getNormalizedModel(request.model) || request.model;
 
-  logDebug(null, `Transforming responses request: model=${request.model} -> ${normalizedModel}`);
+  logDebug(
+    null,
+    `Transforming responses request: model=${request.model} -> ${normalizedModel}`,
+  );
 
   const codexInstructions = await getCodexInstructions(normalizedModel);
   const reasoningConfig = getReasoningConfig(
@@ -116,7 +136,10 @@ export async function transformResponsesRequest(
     ...request,
     model: normalizedModel,
     input: filterInput(
-      request.input || (request.messages ? messagesToInput(request.messages as Message[]) : undefined),
+      request.input ||
+        (request.messages
+          ? messagesToInput(request.messages as Message[])
+          : undefined),
     ),
     stream: request.stream !== undefined ? request.stream : true,
     store: request.store !== undefined ? request.store : false,