Braintrust vs Weights & Biases (2026)
Updated March 9, 2026
Overview
Braintrust is an LLM evaluation and observability platform. Compare its evals, tracing, pricing, pros and cons, and alternatives.
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.
- Experiments comparing prompts and models
- Code-based and LLM-as-judge scorers
- Datasets built from production traces
- Production logging and tracing
- 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
- Unlimited users on every plan, including free
- Production traces, datasets, and experiments connect in one eval workflow
- Framework-agnostic SDKs across multiple languages
- Loop agent drafts scorers and datasets from your own data
Cons
- Processed data and scores bill separately, and both grow with eval volume
- 14-day retention on Starter and 30 days on Pro
- Gateway is in public preview with no SLA
- Self-hosting and custom data export are Enterprise only
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
Braintrust or Weights & — which should you choose?
Choose Braintrust if you wantChoose if you want
- Iterating on prompts with production data
- Running evaluations across model versions
- Building golden datasets from production traffic
- Human review of LLM outputs
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 Braintrust and Weights & Biases on your own traffic
Respan lets you trace LLM and agent calls across any model or framework, A/B test prompts on production traffic, and route requests across 1,000+ models through one gateway.
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