LLM API cost attribution playbook for production SaaS teams

TL;DR If your SaaS product calls multiple LLM providers, the invoice from OpenAI, Anthropic, Gemini, Bedrock, or OpenRouter is not enough. You need attribution at the feature, tenant, assistant, thread, model, and provider level. Otherwise every product experiment turns into one blended AI bill. A practical LLM cost attribution stack has four layers: One OpenAI-compatible gateway endpoint so apps route through a shared control point. Scoped API keys per app, customer, assistant, or workfl...