Together AI is a cloud platform for running, fine-tuning, and deploying open-source large language models at scale. It offers inference APIs for over 100 models (Llama 4, Mistral, Qwen, DeepSeek, etc.) with industry-leading speed and OpenAI-compatible endpoints. Unique features include custom model fine-tuning with proprietary ISP technique, dedicated GPU clusters, and a playground for prompt exploration. Used by researchers, enterprises, and developers who want control over their AI stack without managing GPU infrastructure.