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OpenRouter is a unified API gateway to hundreds of models from every major provider (Anthropic, OpenAI, Google, Mistral, Meta, DeepSeek, and more). One API key, one billing relationship, hundreds of models. This is the right pick when you want to A/B test models freely, avoid lock-in, or simplify procurement.

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Installation

pip install -U swarms

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Environment Setup

export OPENROUTER_API_KEY="sk-or-..."
Get an API key at openrouter.ai/keys.

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Quick Start

OpenRouter model names follow the pattern openrouter/<provider>/<model>: 
from swarms import Agent

agent = Agent(
    agent_name="OpenRouter-Agent",
    model_name="openrouter/anthropic/claude-3.5-sonnet",
    max_loops=1,
)

print(agent.run("Summarize the case for API gateways in three paragraphs."))
Modelmodel_name
Claude 3.5 Sonnet"openrouter/anthropic/claude-3.5-sonnet"
Claude Opus 4.8"openrouter/anthropic/claude-opus-4-8"
GPT-4.1"openrouter/openai/gpt-4.1"
GPT-5.4"openrouter/openai/gpt-5.4"
Gemini 2.5 Pro"openrouter/google/gemini-2.5-pro"
Llama 3.3 70B"openrouter/meta-llama/llama-3.3-70b-instruct"
Qwen 2.5 72B"openrouter/qwen/qwen-2.5-72b-instruct"
DeepSeek R1"openrouter/deepseek/deepseek-r1"
Mistral Large"openrouter/mistralai/mistral-large"
Browse the full catalog for hundreds more.

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Tool Use

Tools work on OpenRouter for any underlying model that supports function calling: 
from swarms import Agent

def get_weather(city: str) -> str:
    """Return the current weather for a city."""
    return f"{city}: 21°C, partly cloudy"

agent = Agent(
    agent_name="OpenRouter-Assistant",
    model_name="openrouter/anthropic/claude-3.5-sonnet",
    tools=[get_weather],
    max_loops=3,
)

print(agent.run("What's the weather in Tokyo right now?"))

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Streaming

from swarms import Agent

agent = Agent(
    agent_name="Streaming-OpenRouter",
    model_name="openrouter/openai/gpt-4.1",
    streaming_on=True,
    max_loops=1,
)

agent.run("Walk me through how a B-tree index works in a relational database.")

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A/B Testing Models

Because every model is available through the same key, OpenRouter is ideal for running side-by-side comparisons: 
from swarms import Agent, ConcurrentWorkflow

candidates = [
    "openrouter/anthropic/claude-3.5-sonnet",
    "openrouter/openai/gpt-4.1",
    "openrouter/google/gemini-2.5-pro",
    "openrouter/meta-llama/llama-3.3-70b-instruct",
]

agents = [
    Agent(
        agent_name=name.split("/")[-1],
        model_name=name,
        system_prompt="Answer in under 150 words.",
        max_loops=1,
    )
    for name in candidates
]

workflow = ConcurrentWorkflow(agents=agents)
results = workflow.run("What are the most underrated trade-offs in monolithic vs. microservice architectures?")

for name, response in results.items():
    print(f"\n=== {name} ===\n{response}")

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Provider Routing

OpenRouter automatically routes between provider hosts for the same model. You can pin to a specific provider or let OpenRouter pick the cheapest/fastest: 
from swarms import Agent

# Let OpenRouter route automatically
agent = Agent(
    agent_name="Auto-Routed",
    model_name="openrouter/meta-llama/llama-3.3-70b-instruct",
    max_loops=1,
)

# See https://openrouter.ai/docs#provider-routing for advanced provider preferences

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Production Defaults

from swarms import Agent

agent = Agent(
    agent_name="Production-OpenRouter",
    model_name="openrouter/anthropic/claude-3.5-sonnet",
    max_loops=1,
    persistent_memory=True,
    context_compression=True,
    context_length=128_000,
    autosave=True,
    retry_attempts=3,
    print_on=False,
)

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Next Steps