How to beginner · 3 min read

How to use system instruction in Gemini API

Q: How to use system instruction in Gemini API

Use the system parameter in the client.chat.completions.create method to provide system instructions in the Gemini API. This parameter sets the assistant's behavior context separate from user messages.

Quick answer

Use the system parameter in the client.chat.completions.create method to provide system instructions in the Gemini API. This parameter sets the assistant's behavior context separate from user messages.

PREREQUISITES

Python 3.8+
OpenAI API key
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 environment: 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

Use the system parameter to specify system instructions that guide the assistant's behavior, distinct from user messages. Below is a complete example using the Gemini model gemini-1.5-pro with the OpenAI SDK v1 pattern.

python

import os
from openai import OpenAI

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

response = client.chat.completions.create(
    model="gemini-1.5-pro",
    system="You are a helpful assistant that responds concisely.",
    messages=[
        {"role": "user", "content": "Explain the benefits of using system instructions."}
    ]
)

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

output

System instructions help set the assistant's behavior and tone, ensuring responses are concise and relevant.

Common variations

You can use different Gemini models like gemini-1.5-flash or gemini-2.0-flash by changing the model parameter. For asynchronous calls, use async client methods if supported. Streaming responses require additional handling with the SDK's streaming interface.

Troubleshooting

If you receive errors about missing system parameter, ensure you are using the latest OpenAI SDK v1 and that the parameter is correctly named. If the assistant ignores system instructions, verify the model supports system prompts and that your API key has access.

✅

Key Takeaways

Use the system parameter to set assistant behavior in Gemini API calls.
Always use the OpenAI SDK v1 pattern with client.chat.completions.create for Gemini models.
Set your API key securely via environment variables to avoid exposure.
Different Gemini models support system instructions similarly; adjust model as needed.
Check SDK version and model access if system instructions are not applied.

Verified 2026-04 · gemini-1.5-pro, gemini-1.5-flash, gemini-2.0-flash

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