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Responses API Overview

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Responses API vs Chat Completions API

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When to Use Responses API

• Need built-in tools (web search, file search)
• Multi-step tasks and complex tool calling
• Need rich streaming events
• Using advanced features of newer models like GPT-5

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When to Use Chat Completions API

• Need the broadest model compatibility
• Simple conversations and text generation
• Existing code based on Chat Completions
• Using non-OpenAI models (Claude, Gemini, etc.)

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Quick Comparison Example

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://crazyrouter.com/v1"
)

response = client.responses.create(
    model="gpt-4o",
    input="Explain what a REST API is"
)

print(response.output_text)

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://crazyrouter.com/v1"
)

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[
        {"role": "user", "content": "Explain what a REST API is"}
    ]
)

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