Weights & Biases Weave: LLM Tracing Inside an Experiment-Tracking House
Your ML team already logs training runs and model artifacts in Weights & Biases — do LLM apps need a second, separate vendor? W&B Weave brings LLM-app observability into the experiment-tracking house: decorate any function with @weave.op and every call is traced with lineage, plus datasets, scorers, evaluate() experiments, and live production monitors sharing the same org, auth, and dashboards as classical ML.
01.The Problem: You Already Live in W&B — Do You Need a Second House?
Start with a situation many teams had in 2024.
Your company does classical ML. Model training runs are logged everywhere the same way:
- every experiment has a run with hyperparameters, metrics curves, and system stats;
- every trained model and dataset is a versioned artifact in the registry;
- dashboards, alerts, accounts, and permissions all exist already, in Weights & Biases.
Then someone ships an LLM copilot. And the observability conversation starts over from zero: a new category of tools (Topics 289–293), a new vendor, a new login, a new trace store, a new dataset copy, new questions from security about data residency.
So the question becomes
Does LLM-app telemetry really need its own separate house — or can it move into the one your ML org already maintains?
That second option is exactly the bet behind Weave — launched 2024 by Weights & Biases, the LLM-app layer of a platform that today sits under the CoreWeave umbrella following the 2025 W&B acquisition.
And to make the whole topic concrete, one plain definition first: LLM-app observability means recording what every model call and agent step received, returned, cost, and produced — so you can debug and measure it later.
Weave within the W&B house
Weave within the W&B house
Weave is LLM-app tracing/evals sharing a platform spine with classic W&B experiment tracking — attractive to teams whose ML group already lives in W&B for models and datasets.
Unlock Topic #292: Weights & Biases Weave: LLM Tracing Inside an Experiment-Tracking House
You are viewing a preview. The full in-depth technical walkthrough, worked derivations, and code notebooks for this concept, along with self-assessment quizzes, are available with Pro or Lifetime Access.
Failure modes, high-throughput bottlenecks, and real FAANG implementation decisions.
Interactive system topology diagrams, live parameter simulators, and downloadable SVG charts.
Staff-level multiple-choice quiz questions with instant feedback and answer explanations.
Firebase Google authentication automatically syncs your completed topics and quiz scores.
How clear and actionable was this distributed systems breakdown?