MLflow vs Weights & Biases (2026)
Updated March 27, 2026
Overview
MLflow is an open-source AI engineering platform for agents, LLMs, and ML models, with tracing, evals, prompt management, and an AI gateway.
Weights & Biases (W&B) is the leading experiment tracking and ML operations platform, now extended to LLM applications. W&B Traces provides observability for LLM pipelines, while W&B Weave offers evaluation and production monitoring. The platform also supports model training tracking, hyperparameter sweeps, and artifact management, making it a comprehensive MLOps solution.
Key features
Core capabilities each platform advertises.
- OpenTelemetry-based tracing for LLMs and agents
- 50+ built-in eval metrics and LLM judges
- Prompt versioning and automatic prompt optimization
- AI Gateway with routing, rate limiting, and fallbacks
- Agent server for deploying agents on FastAPI
- ML experiment tracking
- Model and dataset versioning
- Collaborative dashboards
- Sweeps for hyperparameter tuning
- Prompt monitoring and evaluation
Strengths and tradeoffs
What each tool does well, and the limitations to keep in mind.
Pros
- Apache 2.0 license with Linux Foundation governance
- Tracing, evals, prompts, and a gateway in one open-source project
- Covers classic ML and GenAI in the same platform
- Managed options on Databricks, SageMaker AI, and Azure ML
- Auth and role-based access built into the open-source server
Cons
- Self-hosting means running the tracking server, database, and artifact store yourself
- Auth and role-based access are opt-in and need configuring on self-hosted servers
- Managed versions bill through a cloud platform's compute rather than a standalone plan
- The broader ML scope can mean more to learn for teams that only need LLM tooling
Pros
- Free tier for personal projects and academic research provides excellent value
- Comprehensive experiment tracking and model versioning capabilities
- Strong visualization tools help teams understand model performance
- Acquisition by CoreWeave provides infrastructure synergies and stability
Cons
- Pricing can become expensive for large teams and enterprises
- Additional storage costs can add up quickly for data-intensive workflows
- Learning curve for advanced features may slow initial adoption
- Platform complexity may be overkill for simple ML projects
MLflow or Weights & — which should you choose?
Choose MLflow if you wantChoose if you want
- Tracing and evaluating LLM apps and agents
- Versioning and optimizing prompts
- Routing LLM traffic through a self-hosted gateway
- Tracking classic ML experiments alongside GenAI work
- Running AI tooling inside Databricks
Choose Weights & if you wantChoose if you want
- ML experiment tracking and comparison
- Model training run management
- Team collaboration on ML projects
- Hyperparameter optimization
- Model registry and versioning
Compare MLflow and Weights & Biases on your own traffic
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