A1111 is an open-source web UI for Stable Diffusion, created in August 2022, which offers a beginner-friendly interface with built-in common workflows such as text-to-image and image-to-image. However, its reliability has been criticized and it lacks cutting-edge features like Flux. On the other hand, ComfyUI, launched in January 2023, is a more powerful and flexible version of A1111, allowing users to define workflows down to the node level in a flowchart-like UI and offering more flexibility and customizability. With its strong momentum and pace of development, ComfyUI is likely more future-proof, but also has a steeper learning curve. Both tools can be used simultaneously for different purposes, with A1111 suitable for rapid prototyping and ComfyUI for serving complex workflows in production. Running both on Modal's serverless infrastructure allows users to avoid installation headaches and only pay for GPU time used.