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AI Gateway

The LeanMCP AI Gateway provides a unified API proxy for multiple LLM providers with built-in authentication, token tracking, and observability.

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Features

Multi-Provider Support

OpenAI, Anthropic, xAI (Grok), Fireworks, ElevenLabs

Drop-in Replacement

Use official SDKs or LangChain with minimal code changes

Authentication

Firebase JWT or API key authentication

Session Tracking

Track requests across sessions for observability

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Supported Providers

ProviderEndpointFeatures
OpenAI/v1/openai/*Chat, Vision, DALL-E, TTS, Structured Output
Anthropic/v1/anthropic/*Messages, Vision, Structured Output
xAI (Grok)/v1/xai/*Chat with Web Search
Fireworks/v1/fireworks/*Open-source models (Llama, etc.)
ElevenLabs/v1/elevenlabs/*Text-to-Speech

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Authentication

All requests require authentication via the Authorization header: 
Authorization: Bearer <your-token>
Supported token types:
  • Firebase JWT: Standard Firebase ID token from your app
  • API Key: LeanMCP API keys (prefixed with leanmcp_)

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Usage Examples

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OpenAI SDK

Use the OpenAI SDK by simply changing the baseURL: 
import OpenAI from 'openai';

const client = new OpenAI({
  baseURL: 'https://aigateway.leanmcp.com/v1/openai/v1',
  apiKey: 'your-leanmcp-token', // Firebase JWT or API key
});

// Streaming chat completion
const stream = await client.chat.completions.create({
  model: 'gpt-5.2',
  messages: [
    { role: 'user', content: 'Write a haiku about APIs.' }
  ],
  stream: true,
});

for await (const chunk of stream) {
  const content = chunk.choices[0]?.delta?.content || '';
  process.stdout.write(content);
}

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Anthropic SDK

import Anthropic from '@anthropic-ai/sdk';

const client = new Anthropic({
  baseURL: 'https://aigateway.leanmcp.com/v1/anthropic',
  apiKey: 'your-leanmcp-token',
});

const stream = await client.messages.stream({
  model: 'claude-sonnet-4-5',
  max_tokens: 300,
  messages: [
    { role: 'user', content: 'Write a haiku about cloud computing.' }
  ],
});

for await (const event of stream) {
  if (event.type === 'content_block_delta' && event.delta.type === 'text_delta') {
    process.stdout.write(event.delta.text);
  }
}

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LangChain (Python)

LangChain provides a powerful abstraction for building LLM applications. The AI Gateway works seamlessly with LangChain by simply changing the base_url parameter. 
from langchain_openai import ChatOpenAI
from langchain_core.messages import HumanMessage

# Create ChatOpenAI with gateway configuration
llm = ChatOpenAI(
    model="gpt-5.2",
    base_url="https://aigateway.leanmcp.com/v1/openai/v1",
    api_key="your-leanmcp-token",  # Firebase JWT or API key
    temperature=0.7,
)

# Basic chat completion
response = llm.invoke([
    HumanMessage(content="Write a haiku about APIs.")
])
print(response.content)

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Streaming with LangChain

from langchain_openai import ChatOpenAI
from langchain_core.messages import HumanMessage

llm = ChatOpenAI(
    model="gpt-5.2",
    base_url="https://aigateway.leanmcp.com/v1/openai/v1",
    api_key="your-leanmcp-token",
    streaming=True,
)

# Token-by-token streaming
for chunk in llm.stream([
    HumanMessage(content="Explain quantum computing in 3 sentences.")
]):
    print(chunk.content, end="", flush=True)

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Structured Output with Pydantic

from typing import List
from pydantic import BaseModel, Field
from langchain_openai import ChatOpenAI
from langchain_core.messages import HumanMessage

# Define Pydantic models
class Step(BaseModel):
    step_number: int = Field(description="The step number")
    title: str = Field(description="Brief title of the step")
    description: str = Field(description="Detailed description")

class Recipe(BaseModel):
    name: str = Field(description="Name of the recipe")
    cuisine: str = Field(description="Type of cuisine")
    prep_time_minutes: int = Field(description="Prep time in minutes")
    ingredients: List[str] = Field(description="List of ingredients")
    steps: List[Step] = Field(description="Cooking steps")

llm = ChatOpenAI(
    model="gpt-5.2",
    base_url="https://aigateway.leanmcp.com/v1/openai/v1",
    api_key="your-leanmcp-token",
    temperature=0,
)

# Get structured output
structured_llm = llm.with_structured_output(Recipe)
recipe: Recipe = structured_llm.invoke([
    HumanMessage(content="Give me a recipe for pasta carbonara.")
])

print(f"Recipe: {recipe.name}")
print(f"Ingredients: {recipe.ingredients}")

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Tool Calling with LangChain

from langchain_openai import ChatOpenAI
from langchain_core.messages import HumanMessage
from langchain_core.tools import tool

@tool
def get_weather(city: str, unit: str = "celsius") -> str:
    """Get the current weather for a city."""
    # Your weather API logic here
    return f"Weather in {city}: 22C, Sunny"

@tool
def calculate(expression: str) -> str:
    """Calculate a mathematical expression."""
    return f"Result: {eval(expression)}"

llm = ChatOpenAI(
    model="gpt-5.2",
    base_url="https://aigateway.leanmcp.com/v1/openai/v1",
    api_key="your-leanmcp-token",
    temperature=0,
)

# Bind tools to the model
tools = [get_weather, calculate]
llm_with_tools = llm.bind_tools(tools)

response = llm_with_tools.invoke([
    HumanMessage(content="What's the weather in London and calculate 25 * 4?")
])

# Process tool calls
for tool_call in response.tool_calls:
    print(f"Tool: {tool_call['name']}, Args: {tool_call['args']}")

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Multi-Model Chains

Orchestrate multiple providers in a single LangChain workflow: 
from langchain_openai import ChatOpenAI
from langchain_anthropic import ChatAnthropic
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.output_parsers import StrOutputParser

# Create both LLMs
openai_llm = ChatOpenAI(
    model="gpt-5.2",
    base_url="https://aigateway.leanmcp.com/v1/openai/v1",
    api_key="your-leanmcp-token",
)

anthropic_llm = ChatAnthropic(
    model="claude-sonnet-4-5",
    base_url="https://aigateway.leanmcp.com/v1/anthropic",
    api_key="your-leanmcp-token",
    max_tokens=300,
)

# Step 1: OpenAI generates content
generator_prompt = ChatPromptTemplate.from_messages([
    ("system", "Generate a short story premise (2-3 sentences)."),
    ("human", "Topic: {topic}"),
])

# Step 2: Anthropic critiques
critic_prompt = ChatPromptTemplate.from_messages([
    ("system", "Review and suggest one improvement for this story premise."),
    ("human", "Premise: {premise}"),
])

output_parser = StrOutputParser()

# Build chains
generator_chain = generator_prompt | openai_llm | output_parser
critic_chain = critic_prompt | anthropic_llm | output_parser

# Execute multi-model workflow
premise = generator_chain.invoke({"topic": "a robot learning to dream"})
critique = critic_chain.invoke({"premise": premise})

print(f"Generated: {premise}")
print(f"Critique: {critique}")
Requirements: Install LangChain packages:
pip install langchain-openai langchain-anthropic langchain-core

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curl Examples

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OpenAI Streaming

curl -N -X POST "https://aigateway.leanmcp.com/v1/openai/v1/chat/completions" \
  -H "Authorization: Bearer $AUTH_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.2",
    "messages": [{"role": "user", "content": "Hello!"}],
    "stream": true
  }'

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Anthropic Messages

curl -X POST "https://aigateway.leanmcp.com/v1/anthropic/v1/messages" \
  -H "Authorization: Bearer $AUTH_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5",
    "max_tokens": 300,
    "messages": [{"role": "user", "content": "Hello!"}]
  }'

curl -N -X POST "https://aigateway.leanmcp.com/v1/xai/v1/chat/completions" \
  -H "Authorization: Bearer $AUTH_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "grok-2-latest",
    "messages": [{"role": "user", "content": "What are the top tech news today?"}],
    "stream": true,
    "search_parameters": {"mode": "auto"}
  }'

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Fireworks (Llama)

curl -N -X POST "https://aigateway.leanmcp.com/v1/fireworks/inference/v1/chat/completions" \
  -H "Authorization: Bearer $AUTH_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "accounts/fireworks/models/llama-v3p1-8b-instruct",
    "messages": [{"role": "user", "content": "Explain quantum computing."}],
    "stream": true,
    "max_tokens": 100
  }'

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ElevenLabs TTS

curl -X POST "https://aigateway.leanmcp.com/v1/elevenlabs/v1/text-to-speech/21m00Tcm4TlvDq8ikWAM" \
  -H "Authorization: Bearer $AUTH_TOKEN" \
  -H "Content-Type: application/json" \
  -o "output.mp3" \
  -d '{
    "text": "Hello! This is a test.",
    "model_id": "eleven_monolingual_v1",
    "voice_settings": {"stability": 0.5, "similarity_boost": 0.5}
  }'

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Advanced Features

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Structured Output (OpenAI)

const response = await fetch('https://aigateway.leanmcp.com/v1/openai/v1/chat/completions', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${token}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    model: 'gpt-5.2',
    messages: [
      { role: 'user', content: 'Recommend 3 sci-fi movies from the 2010s.' }
    ],
    response_format: {
      type: 'json_schema',
      json_schema: {
        name: 'movie_recommendations',
        strict: true,
        schema: {
          type: 'object',
          properties: {
            recommendations: {
              type: 'array',
              items: {
                type: 'object',
                properties: {
                  title: { type: 'string' },
                  year: { type: 'number' },
                  genre: { type: 'string' },
                  reason: { type: 'string' },
                },
                required: ['title', 'year', 'genre', 'reason'],
              },
            },
          },
          required: ['recommendations'],
        },
      },
    },
  }),
});

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Session Tracking

Include a session ID to track requests across a conversation: 
curl -X POST "https://aigateway.leanmcp.com/v1/openai/v1/chat/completions" \
  -H "Authorization: Bearer $AUTH_TOKEN" \
  -H "Content-Type: application/json" \
  -H "leanmcp-session-id: my-session-123" \
  -d '{"model": "gpt-5.2", "messages": [...]}'

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Bring Your Own API Key

To use your own provider API key instead of platform keys: 
curl -X POST "https://aigateway.leanmcp.com/v1/anthropic/v1/messages" \
  -H "Authorization: Bearer $AUTH_TOKEN" \
  -H "x-provider-api-key: sk-ant-your-key" \
  -H "Content-Type: application/json" \
  -d '{...}'