Gemini API
ai.google.devAI
Google's answer, with real native multimodal input and a free tier generous enough to actually prototype on.
Other products from AI
The default LLM API for a reason — GPT models, huge ecosystem, and every tutorial assumes you're using it.
Claude's own maker — strong reasoning and long context, built with more thought given to safety than most.
European and more open about its weights than the US giants, usually cheaper too if that matters to you.