LLM Gateway Architecture: When You Need One and How to Get Started

The monthly cloud invoice came in $12K higher than expected and nobody can explain it. Engineering added Opus for a summarization feature... Product had QA testing vision with GPT-4o... the data team switched from Sonnet to a fine-tuned model on Bedrock three weeks ago and forgot to mention it. This is the database connection problem, replayed for LLMs. Every service talking directly to an external provider, no abstraction layer, no visibility, no fallback. You solved this for database connections a decade ago with connection pools. The LLM gateway is the same pattern, and most mid-market engineering teams don't have one yet. What an LLM Gateway Actually Does An LLM gateway sits between your application code and your model providers. Instead of each service importing the OpenAI SDK or the Anthropic SDK or the Bedrock client and calling providers directly, every request routes through a single layer. Your code talks to the gateway. The gateway talks to the providers. Think API gateway (