How to beginner · 3 min read

How to pass context in OpenAI thread messages

Quick answer

To pass context in OpenAI thread messages, include the full conversation history as a list of messages with roles (user, assistant, system) in each API call. Use the client.chat.completions.create method with the messages parameter containing prior messages to maintain context across turns.

PREREQUISITES

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

Setup

Install the official OpenAI Python SDK and set your API key as an environment variable.

Run pip install openai to install the SDK.
Set your API key in your shell: export OPENAI_API_KEY='your_api_key_here' (Linux/macOS) or setx OPENAI_API_KEY "your_api_key_here" (Windows).

bash

pip install openai

Step by step

Pass the full conversation history as a list of messages to maintain context in the thread. Each message is a dictionary with role and content. The system role sets behavior, user is user input, and assistant is the AI's prior responses.

python

import os
from openai import OpenAI

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

# Conversation history with context
messages = [
    {"role": "system", "content": "You are a helpful assistant."},
    {"role": "user", "content": "Hello, who won the world series in 2020?"},
    {"role": "assistant", "content": "The Los Angeles Dodgers won the World Series in 2020."},
    {"role": "user", "content": "Where was it played?"}
]

response = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=messages
)

print(response.choices[0].message.content)

output

The 2020 World Series was played at Globe Life Field in Arlington, Texas.

Common variations

You can use different models like gpt-4.1 or gpt-4o-mini by changing the model parameter. For asynchronous calls, use async libraries or frameworks. Streaming responses require additional handling with event loops or callbacks, which the OpenAI Python SDK supports via separate methods.

Troubleshooting

If the context is lost, ensure you pass the entire message history every time you call client.chat.completions.create.
Check that roles are correctly assigned; system for instructions, user for user inputs, and assistant for AI replies.
Verify your API key is set correctly in os.environ.

✅

Key Takeaways

Always pass the full conversation history in the messages parameter to maintain context.
Use the system role message to set assistant behavior at the start of the thread.
Each API call must include prior user and assistant messages to keep the thread coherent.

Verified 2026-04 · gpt-4o-mini, gpt-4.1, gpt-4o-mini

Verify ↗