curl -X POST 'https://api.openai.com/v1/threads/thread-id/messages/message-id' \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{}'

# POST /threads/{thread_id}/messages/{message_id} (OpenAI API)
Base URL: https://api.openai.com/v1
Auth: Authorization; OpenAI API key; required.
Request formats: application/json.
Last verified: 2026-10-20

> Modify message

## Critical Gotchas
* The Responses API is the primary interface for new text and tool workflows; Chat Completions remains a separate compatibility API.
* Audio transcription uploads use multipart form data rather than a JSON request body.

## cURL
curl -X POST 'https://api.openai.com/v1/threads/thread-id/messages/message-id' \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{}'

## Parameters
| Name | In | Type | Required | Description |
| :--- | :--- | :--- | :--- | :--- |
| thread_id | path | string | Yes | The ID of the thread to which this message belongs. |
| message_id | path | string | Yes | The ID of the message to modify. |
| metadata | body | object | No | Set of 16 key-value pairs that can be attached to an object. This can be usef... |

## Response example
{"id":"string","object":"thread.message"}

---
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POST

POST /threads/{thread_id}/messages/{message_id} — OpenAI API

OpenAI API key (required); https://api.openai.com/v1

OpenAI API

Modify message

Base URL: https://api.openai.com/v1
Auth: Authorization: Bearer <OPENAI_API_KEY>
Last verified: 2026-10-20 · upstream hash matched

Actions Try in browser→

Agents: curl -H "Accept: text/markdown" this URL
→ 233 tokens · Vary: Accept

Critical gotchas

The Responses API is the primary interface for new text and tool workflows; Chat Completions remains a separate compatibility API.

Audio transcription uploads use multipart form data rather than a JSON request body.

cURL

curl -X POST 'https://api.openai.com/v1/threads/thread-id/messages/message-id' \  -H "Authorization: Bearer $OPENAI_API_KEY" \  -H 'Content-Type: application/json' \  -d '{}'

Parameters

Name	In	Type	Required	Description
thread_id	path	string	Yes	The ID of the thread to which this message belongs.
message_id	path	string	Yes	The ID of the message to modify.
metadata	body	object	No	Set of 16 key-value pairs that can be attached to an object. This can be useful for storing additional information about the object in a structured format, and querying for objects via API or the dashboard. Keys are strings with a maximum length of 64 characters. Values are strings with a maximum length of 512 characters.

Response 200 OK

{
  "id": "string",
  "object": "thread.message",
  "created_at": 0,
  "thread_id": "string",
  "status": "in_progress",
  "incomplete_details": {
    "reason": "content_filter"
  },
  "completed_at": 0,
  "incomplete_at": 0,
  "role": "user",
  "content": [
    {
      "type": "image_file",
      "image_file": {
        "file_id": "string",
        "detail": "auto"
      }
    }
  ],
  "assistant_id": "string",
  "run_id": "string",
  "attachments": [
    {
      "file_id": "string",
      "tools": [
        {
          "type": "code_interpreter"
        }
      ]
    }
  ],
  "metadata": {}
}

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