Google published Imagen in the paper "Photorealistic Text-to-Image Diffusion Models with Deep Language Understanding," combining text understanding from large Transformer language models with high-fidelity image generation from diffusion models. It set a then-best FID score of 7.27 on COCO without ever training on it, and human raters judged its samples on par with real COCO data for image-text alignment. It came six weeks after OpenAI put DALL-E 2 into limited release, but Google declined to make Imagen publicly available, citing concerns about harmful content and the reproduction of social bias. Holding back a product while leading on the research was characteristic of Google in this period.