OpenAI

AGI-focused research lab producing the GPT and o-series model families. Deploys transformer-based LLMs with RLHF and reinforcement fine-tuning; o-series uses chain-of-thought reasoning at inference time. Offers hosted API, Agents SDK, and Responses API for multi-step agentic workflows. Also ships DALL-E, Sora, Whisper, and multimodal realtime audio models.