OpenRouter, Ollama, vLLM, anything that speaks the OpenAI HTTP API. Self-hosted models work too.
API key
quota / cost —
!
ChatGPT Plus and Claude.ai are not API keys.The €20/mo ChatGPT subscription and the €18/mo Claude.ai subscription are for the chat apps only. To plug a model into your agent, you need an API key — separate billing, pay-per-token. The voice agent will explain in plain English if you ask.