# Useful but Little-Known Features of OpenAI Agent SDK
🌍 Ever wanted to mix multiple LLM providers within a single agent system?
`MultiProvider` automatically routes requests to the right provider based on model name prefixes.
📌 Title: Prefix Routing with MultiProvider
🔗 URL:
🧩 Overview
`MultiProvider` routes requests to the appropriate provider based on model name prefixes (e.g., `openai/gpt-4.1`). Setting `openai_prefix_mode="model_id"` treats `openai/...` as a literal model ID, while `unknown_prefix_mode="model_id"` routes unknown prefixes as model IDs too. Enable `openai_use_responses_websocket=True` for WebSocket transport on supported providers.
🛠 How to use it
```python
from agents import Agent, MultiProvider, RunConfig, Runner
provider = MultiProvider(
openai_base_url="",
openai_api_key="...",
openai_use_responses_websocket=True,
openai_prefix_mode="model_id",
unknown_prefix_mode="model_id",
)
agent = Agent(
name="Assistant",
instructions="Be concise.",
model="openai/gpt-4.1",
)
result = await
agent,
"Hello",
run_config=RunConfig(model_provider=provider),
)
```
🏗 Building it into production
・Assign different provider models to each agent based on cost and latency requirements
・Combine with gateway services like OpenRouter using `openai_prefix_mode="model_id"` to pass prefixed model names through
・Switch providers at runtime via `RunConfig(model_provider=provider)` for A/B testing
・Enable WebSocket for improved streaming performance on supported providers
💡 Use cases
🔀 Routing GPT-4.1 vs GPT-5.5 based on task difficulty
🌐 Unified access to multiple providers through OpenRouter
💰 Hybrid operation mixing high-cost and low-cost models
🧪 Quality comparison testing across different models
⚠️ Watch out
By default, `openai/...` aliases to the OpenAI provider, and unknown prefixes raise `UserError`. When using external gateways like OpenRouter, always set both `openai_prefix_mode` and `unknown_prefix_mode` to `"model_id"`. Note that feature support (tool calling, structured output, etc.) varies across providers.
✨ With MultiProvider, build agent systems that freely combine the best models from any provider.
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