How can I append new user and assistant messages to an existing thread using the Assistant API?

Below is a concise explanation with an example in Python:

Persistent Threads for Chat Sessions

A thread is designed to be a persistent conversation session. You do not need to recreate a new thread for every turn of the chat. Instead, you can append new messages (from both users and assistants) to an existing thread using the provided API.

How to Append New Messages

Once you have created a thread, you can add new messages by calling the endpoint to create a message. For example, using the Python SDK:

PYTHONCopied
message = client.beta.threads.messages.create(
  thread_id=thread.id,
  role="user",  # or "assistant" for assistant messages
  content="Your new message here"
)

Each new message is appended to the thread, helping maintain conversation history. The thread will also automatically handle truncation of older messages when the context window is exceeded, ensuring that the most important context is preserved.

Summary

• No need to create a new thread each turn: The persistent thread allows multiple messages.
• Append messages as you go: Use the messages creation API to add both user and assistant messages.
• Context is maintained: The API smartly manages message truncation to fit within the model's context window.

This should enable you to build a chat-like application using persistent threads without recreating threads on every user turn.