OpenRouter Upgrade & Migration

Current State

!npm list openai 2>/dev/null | head -5

!pip show openai 2>/dev/null | head -5

Overview

Migrating to OpenRouter from a direct provider API (OpenAI, Anthropic) is minimal: change baseurl and apikey, add two headers. The OpenAI SDK works natively with OpenRouter. This skill covers migrating from direct APIs, switching between models, upgrading SDK versions, and running comparison tests.

Migration from Direct OpenAI

# BEFORE: Direct OpenAI
from openai import OpenAI
client = OpenAI(api_key=os.environ["OPENAI_API_KEY"])
response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Hello"}],
    max_tokens=200,
)

# AFTER: Via OpenRouter (3 lines changed)
from openai import OpenAI
client = OpenAI(
    base_url="https://openrouter.ai/api/v1",     # ← Changed
    api_key=os.environ["OPENROUTER_API_KEY"],     # ← Changed
    default_headers={                              # ← Added
        "HTTP-Referer": "https://my-app.com",
        "X-Title": "my-app",
    },
)
response = client.chat.completions.create(
    model="openai/gpt-4o",  # ← Add provider prefix
    messages=[{"role": "user", "content": "Hello"}],
    max_tokens=200,
)

Migration from Direct Anthropic

# BEFORE: Direct Anthropic SDK
import anthropic
client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])
response = client.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=200,
    messages=[{"role": "user", "content": "Hello"}],
)
content = response.content[0].text

# AFTER: Via OpenRouter (using OpenAI SDK instead of Anthropic SDK)
from openai import OpenAI
client = OpenAI(
    base_url="https://openrouter.ai/api/v1",
    api_key=os.environ["OPENROUTER_API_KEY"],
    default_headers={
        "HTTP-Referer": "https://my-app.com",
        "X-Title": "my-app",
    },
)
response = client.chat.completions.create(
    model="anthropic/claude-3.5-sonnet",  # OpenRouter model ID
    messages=[{"role": "user", "content": "Hello"}],
    max_tokens=200,
)
content = response.choices[0].message.content  # OpenAI response format

TypeScript Migration

// BEFORE: Direct OpenAI
import OpenAI from "openai";
const client = new OpenAI({ apiKey: process.env.OPENAI_API_KEY });

// AFTER: Via OpenRouter
const client = new OpenAI({
  baseURL: "https://openrouter.ai/api/v1",
  apiKey: process.env.OPENROUTER_API_KEY,
  defaultHeaders: {
    "HTTP-Referer": "https://my-app.com",
    "X-Title": "my-app",
  },
});
// Change model from "gpt-4o" to "openai/gpt-4o"

Migration Checklist

MIGRATION_CHECKLIST = {
    "config": [
        "base_url changed to https://openrouter.ai/api/v1",
        "API key changed to OPENROUTER_API_KEY (sk-or-v1-...)",
        "HTTP-Referer and X-Title headers added",
        "Model IDs prefixed with provider/ (e.g., openai/gpt-4o)",
    ],
    "code": [
        "All client initialization updated",
        "Model IDs updated in all routes/configs",
        "Error handling covers OpenRouter-specific codes (402, 408)",
        "Streaming still works with new endpoint",
        "Tool/function calling still works",
    ],
    "testing": [
        "Same prompts produce comparable quality output",
        "Latency within acceptable range (expect +50-100ms)",
        "Token counts match expectations",
        "Cost tracking updated for OpenRouter pricing",
        "Fallback chain tested",
    ],
    "operations": [
        "Credit balance sufficient for expected usage",
        "Per-key credit limits configured",
        "Monitoring updated to track OpenRouter metrics",
        "Alerting on new error codes (402, 408)",
        "Rollback plan documented",
    ],
}

Model ID Migration Map

Comparison Test Script

def compare_migration(prompt: str, old_model: str, new_model: str):
    """Run same prompt through old and new configurations to compare."""
    import time

    # New: OpenRouter
    or_client = OpenAI(
        base_url="https://openrouter.ai/api/v1",
        api_key=os.environ["OPENROUTER_API_KEY"],
        default_headers={"HTTP-Referer": "https://my-app.com", "X-Title": "migration-test"},
    )

    start = time.monotonic()
    or_response = or_client.chat.completions.create(
        model=new_model,
        messages=[{"role": "user", "content": prompt}],
        max_tokens=200, temperature=0,
    )
    or_latency = (time.monotonic() - start) * 1000

    return {
        "openrouter": {
            "model": or_response.model,
            "content": or_response.choices[0].message.content[:100],
            "tokens": or_response.usage.prompt_tokens + or_response.usage.completion_tokens,
            "latency_ms": round(or_latency),
        },
    }

# Test
result = compare_migration(
    "What is 2+2?",
    old_model="gpt-4o",
    new_model="openai/gpt-4o",
)
print(json.dumps(result, indent=2))

Feature Flag Migration

import os

USE_OPENROUTER = os.environ.get("USE_OPENROUTER", "false").lower() == "true"

def get_llm_client():
    """Feature flag for gradual migration."""
    if USE_OPENROUTER:
        return OpenAI(
            base_url="https://openrouter.ai/api/v1",
            api_key=os.environ["OPENROUTER_API_KEY"],
            default_headers={"HTTP-Referer": "https://my-app.com", "X-Title": "my-app"},
        )
    else:
        return OpenAI(api_key=os.environ["OPENAI_API_KEY"])

def get_model_id(model: str) -> str:
    """Map model IDs based on current backend."""
    if USE_OPENROUTER and "/" not in model:
        MODEL_MAP = {"gpt-4o": "openai/gpt-4o", "gpt-4o-mini": "openai/gpt-4o-mini"}
        return MODEL_MAP.get(model, f"openai/{model}")
    return model

Error Handling

Enterprise Considerations

• Migration from direct provider to OpenRouter requires only 3 lines of code change
• Use feature flags for gradual migration (10% -> 50% -> 100%)
• Run comparison tests on critical prompts before full migration
• OpenRouter adds ~50-100ms overhead; use streaming to mask perceived latency
• Keep direct provider keys active during migration for quick rollback
• Update monitoring dashboards for OpenRouter-specific metrics (generation_id, provider used)

References

• Examples | Errors
• Quickstart | OpenAI Compatibility