OpenRouter LLM Provider

The OpenRouter provider connects Beluga AI to OpenRouter, a unified gateway that routes requests to many different model providers (OpenAI, Anthropic, Google, Meta, Mistral, and more). OpenRouter exposes an OpenAI-compatible API, so this provider supports all standard features including streaming, tool calling, and structured output.

Choose OpenRouter when you want to compare models across providers without managing separate API keys, or when you need access to niche models not available through other providers. OpenRouter’s single API key simplifies billing and model switching during development and evaluation.

Installation

go get github.com/lookatitude/beluga-ai/llm/providers/openrouter

Configuration

Field	Required	Default	Description
Model	Yes	—	Model ID (provider/model format)
APIKey	Yes	—	OpenRouter API key (sk-or-...)
BaseURL	No	https://openrouter.ai/api/v1	Override API endpoint
Timeout	No	30s	Request timeout

Environment variables:

Variable	Maps to
OPENROUTER_API_KEY	APIKey

Basic Usage

package main

import (
    "context"
    "fmt"
    "log"
    "os"

    "github.com/lookatitude/beluga-ai/config"
    "github.com/lookatitude/beluga-ai/llm"
    "github.com/lookatitude/beluga-ai/schema"
    _ "github.com/lookatitude/beluga-ai/llm/providers/openrouter"
)

func main() {
    model, err := llm.New("openrouter", config.ProviderConfig{
        Model:  "anthropic/claude-sonnet-4-5-20250929",
        APIKey: os.Getenv("OPENROUTER_API_KEY"),
    })
    if err != nil {
        log.Fatal(err)
    }

    msgs := []schema.Message{
        schema.NewSystemMessage("You are a helpful assistant."),
        schema.NewHumanMessage("What is the capital of France?"),
    }

    resp, err := model.Generate(context.Background(), msgs)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(resp.Text())
}

Streaming

for chunk, err := range model.Stream(context.Background(), msgs) {
    if err != nil {
        log.Fatal(err)
    }
    fmt.Print(chunk.Delta)
}
fmt.Println()

Advanced Features

Accessing Different Providers

OpenRouter uses a provider/model naming convention:

// Use Claude via OpenRouter
model, err := llm.New("openrouter", config.ProviderConfig{
    Model:  "anthropic/claude-sonnet-4-5-20250929",
    APIKey: os.Getenv("OPENROUTER_API_KEY"),
})

// Use GPT-4o via OpenRouter
model, err := llm.New("openrouter", config.ProviderConfig{
    Model:  "openai/gpt-4o",
    APIKey: os.Getenv("OPENROUTER_API_KEY"),
})

// Use Llama via OpenRouter
model, err := llm.New("openrouter", config.ProviderConfig{
    Model:  "meta-llama/llama-3.1-70b-instruct",
    APIKey: os.Getenv("OPENROUTER_API_KEY"),
})

Tool Calling

modelWithTools := model.BindTools(tools)
resp, err := modelWithTools.Generate(ctx, msgs, llm.WithToolChoice(llm.ToolChoiceAuto))

Structured Output

resp, err := model.Generate(ctx, msgs,
    llm.WithResponseFormat(llm.ResponseFormat{Type: "json_object"}),
)

Generation Options

resp, err := model.Generate(ctx, msgs,
    llm.WithTemperature(0.7),
    llm.WithMaxTokens(2048),
    llm.WithTopP(0.9),
)

Error Handling

resp, err := model.Generate(ctx, msgs)
if err != nil {
    log.Fatal(err)
}

Direct Construction

import "github.com/lookatitude/beluga-ai/llm/providers/openrouter"

model, err := openrouter.New(config.ProviderConfig{
    Model:  "anthropic/claude-sonnet-4-5-20250929",
    APIKey: os.Getenv("OPENROUTER_API_KEY"),
})

Available Models

OpenRouter provides access to hundreds of models. Some popular options:

Model ID	Provider	Description
openai/gpt-4o	OpenAI	GPT-4o
anthropic/claude-sonnet-4-5-20250929	Anthropic	Claude Sonnet 4.5
google/gemini-2.5-flash	Google	Gemini 2.5 Flash
meta-llama/llama-3.1-70b-instruct	Meta	Llama 3.1 70B

Refer to OpenRouter’s model list for the full catalog.