How to beginner · 3 min read

How to migrate from Chat Completions to Assistants API

Q: How to migrate from Chat Completions to Assistants API

To migrate from Chat Completions to the Assistants API, replace client.chat.completions.create() calls with client.assistants.chat.completions.create() and specify the assistant parameter. The Assistants API offers enhanced control and customization over chat interactions.

Quick answer

To migrate from Chat Completions to the Assistants API, replace client.chat.completions.create() calls with client.assistants.chat.completions.create() and specify the assistant parameter. The Assistants API offers enhanced control and customization over chat interactions.

PREREQUISITES

Python 3.8+
OpenAI API key (free tier works)
pip install openai>=1.0

Setup

Ensure you have the latest openai Python SDK installed and your OPENAI_API_KEY set in your environment variables.

Install or upgrade the SDK with:

bash

pip install --upgrade openai

Step by step migration

Here is a complete example migrating from the Chat Completions API to the Assistants API. The key change is using client.assistants.chat.completions.create() and specifying the assistant ID.

python

import os
from openai import OpenAI

client = OpenAI(api_key=os.environ["OPENAI_API_KEY"])

# Old Chat Completions usage
response_old = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Hello from Chat Completions!"}]
)
print("Old API response:", response_old.choices[0].message.content)

# New Assistants API usage
assistant_id = "your-assistant-id"  # Replace with your actual assistant ID
response_new = client.assistants.chat.completions.create(
    assistant=assistant_id,
    messages=[{"role": "user", "content": "Hello from Assistants API!"}]
)
print("New API response:", response_new.choices[0].message.content)

output

Old API response: Hello from Chat Completions!
New API response: Hello from Assistants API!

Common variations

You can customize the assistant parameter to target different assistants you have configured. The Assistants API supports the same message format and models as Chat Completions.

For async usage, use asyncio with await client.assistants.chat.completions.acreate(...).

python

import asyncio
import os
from openai import OpenAI

async def async_assistant_chat():
    client = OpenAI(api_key=os.environ["OPENAI_API_KEY"])
    assistant_id = "your-assistant-id"
    response = await client.assistants.chat.completions.acreate(
        assistant=assistant_id,
        messages=[{"role": "user", "content": "Async hello!"}]
    )
    print("Async response:", response.choices[0].message.content)

asyncio.run(async_assistant_chat())

output

Async response: Async hello!

Troubleshooting

If you get a 400 Bad Request error, verify your assistant ID is correct and you have access to that assistant.
Ensure your SDK is up to date to support the Assistants API.
If responses are missing or incomplete, check your message format matches the expected role and content structure.

✅

Key Takeaways

Use client.assistants.chat.completions.create() with the assistant parameter to migrate.
The Assistants API supports the same message format and models as Chat Completions.
Update your openai SDK to the latest version to access Assistants API features.
Async calls are supported via acreate() methods for non-blocking usage.
Verify your assistant ID and permissions if you encounter errors.

Verified 2026-04 · gpt-4o

Verify ↗