LiteLLM

LiteLLM is the open-source standard for putting one interface in front of every LLM provider. It ships as two pieces: a Python SDK for application code and a gateway/proxy you deploy in front of your infrastructure, both speaking the OpenAI format across 100+ provider integrations including Azure, Bedrock, Gemini, OpenAI, and Anthropic. The gateway layer is what production teams come for - per-key spend tracking, budgets, rate limiting, load balancing, and automatic fallbacks when a provider degrades. The project reports 240M+ Docker pulls and over 1,000 GitHub contributors. Where OpenRouter is a hosted multi-model API, LiteLLM is the self-hosted equivalent you control end to end, and the two pair well in a fallback chain.