Which AI providers can I use?

Four — OpenAI, Anthropic, Groq and OpenRouter. You can save a key for each and switch between them. Groq and OpenRouter have genuinely free tiers; OpenAI and Anthropic are paid.

They split into two classes, and the app treats those classes differently throughout.

The paid pair.

• OpenAIKeys begin sk-..., from platform.openai.com. Models offered: GPT-5 mini (the default), GPT-5.1, and GPT-4o mini.
• AnthropicKeys begin sk-ant-..., from console.anthropic.com. Models offered: Claude Haiku 4.5 (the default), Sonnet 5, Opus 5, plus the previous-generation Opus 4.8 and Sonnet 4.6.

The free pair.

• GroqKeys begin gsk_..., from console.groq.com. Runs open models very fast, with a free tier. Also the provider used for voice transcription, which is a separate reason to have a Groq key even if your main provider is elsewhere.
• OpenRouterKeys begin sk-or-..., from openrouter.ai. One key in front of many models, several of which cost nothing.

One thing the tiles get wrong. The OpenAI tile is labelled "OpenAI (GPT-4o / GPT-4o-mini)" and the Groq tile mentions Mixtral. Both labels are stale — the model list underneath each is the accurate one, and it is what actually gets called.