url4

More accurate AI than any single model. The open protocol for AI model ensembles.

Install

pip install url4

Quick Start

import asyncio
from url4 import Council

async def main():
    council = Council("claude-haiku|gpt-4o-mini")
    result = await council.ask("What causes auroras?")
    print(result.response)

asyncio.run(main())

What It Does

url4 queries multiple AI models in parallel and synthesizes their responses into a single, more accurate answer. Like an ensemble in machine learning — but for LLMs.

# Weighted ensemble with custom synthesis instruction
council = Council("0.5*claude-opus|0.3*gpt-4o|0.2*gemini-pro!synthesize the most accurate answer")
result = await council.ask("What is dark matter?")

# Streaming output
async for chunk in council.ask_stream("Explain quantum computing"):
    print(chunk, end="", flush=True)

# Cost estimation before running
estimate = council.estimate("any prompt")
print(f"Estimated cost: ${estimate.total_cost:.4f}")

Features

• Multi-model ensembles — query any combination of Claude, GPT, Gemini, Llama, Mistral, DeepSeek
• Weighted synthesis — control how much each model contributes
• Streaming — stream the synthesis output token by token
• Caching — responses are cached locally so repeated queries are free
• Nested councils — councils of councils for multi-level synthesis
• Progressive reduce — synthesize at checkpoints as models respond
• Cost estimation — estimate costs before executing
• CLI — url4 ask "claude|gpt-4o" "your question"
• Eval harness — benchmark councils against HLE and other datasets

CLI

url4 ask "claude-haiku|gpt-4o-mini" "What is 2+2?"
url4 estimate "claude-opus|gpt-4o" "anything"
url4 models
url4 cache-stats

API Keys

Set the API keys for the providers you want to use:

export ANTHROPIC_API_KEY=sk-ant-...
export OPENAI_API_KEY=sk-...
export OPENROUTER_API_KEY=sk-or-...  # optional: routes to 200+ models

If you have Claude Code installed, url4 can use it as a zero-config fallback — no API keys needed.

The Protocol

url4 is a URL-based grammar for composing AI queries:

claude-haiku|gpt-4o!What is the meaning of life?

Sources left of !, prompt right of !. Pipe | separates sources. Weights with *, nesting with []:

0.5*claude-opus|0.3*[gpt-4o|gemini!draft]|0.2*deepseek!final synthesis

Full spec: url4.ai/spec.html

License

Apache 2.0