Quick answer: ML experiment tracking + LLM observability (W&B Weave).
Weights & Biases (W&B) is an experiment tracking and ML observability platform built by Weights & Biases, Inc. It helps machine learning teams log, visualize, and compare experiments across training runs, datasets, and model configurations. The platform provides dashboards for tracking metrics, hyperparameters, and artifacts in real-time, making it easier to identify what drives model performance. W&B also offers Weave, an LLM observability tool that captures traces of LLM applications—logging inputs, outputs, latency, and costs—enabling debugging and optimization of complex AI workflows. The platform integrates with popular ML frameworks like PyTorch, TensorFlow, and Hugging Face. W&B operates on a freemium model, with free tier access for teams and paid plans for advanced features, making it accessible for startups and enterprises alike.