Comparison
Winnow vs Braintrust
Braintrust is the best pure eval and observability platform. We built Winnow to cover the stages after eval ends: online experiments with real stats, gates and bandits that turn a winning result into a safe rollout, and an agent that reasons about whether you should ship.
The matrix below includes the rows where Braintrust leads. If we were covering every stage of the lifecycle as well as they cover eval, the comparison would not be interesting.
The full matrix
Green check: full support. Yellow dash: partial or competing approach. Blank: not available.
| Feature | Winnow | Braintrust |
|---|---|---|
| Evaluation & datasets | ||
Offline eval suites Both ship the three-primitive (data, task, scores) API. | ||
LLM-as-judge scorers | ||
Golden datasets with versioning | ||
Playground (grid prompt/model compare) Braintrust leads here today. Winnow ships "The Construct" in this release. | ||
Trace-ingestion ergonomics Braintrust's trace upload has fewer sharp edges; Winnow requires SDK init. | ||
| Online experimentation | ||
A/B tests on prompts, models, configs Online experiments are the feature Braintrust does not have. | ||
mSPRT (anytime-valid sequential) | ||
Welch / Bayesian / CUPED | ||
Power analysis on every experiment | ||
SRM (sample-ratio mismatch) detection | ||
Multi-armed bandits | ||
| Shipping & safety | ||
Feature gates (boolean rollouts) | ||
Dynamic configs (typed JSON) | ||
Guardrails with severity levels | ||
Automatic kill switch on breach | ||
| Agents & reasoning | ||
Autonomous optimization agent | ||
Structured second opinion with evidence pointers | ||
could_be_wrong_if refutation conditions | ||
MCP server for IDE agents | ||
| Performance, storage, and deploy | ||
Self-hosted option | ||
Warehouse-grade analytics for cross-experiment | ||
Brainstore-class trace query performance Braintrust publishes specific latency numbers for Brainstore. Winnow is fast but has no equivalent public benchmark yet. | ||
llms.txt for LLM-consumable docs | ||
| Pricing & plans | ||
Free tier that is actually usable Winnow Free: 5M runs/mo. Braintrust Free: 1M traces/mo. | ||
Mid-tier under $150/seat Winnow Pro is $99/seat. Braintrust jumps $0 to $249/seat. | ||
Per-seat pricing with unlimited seats on free/pro | ||
Three contrasts that hold against any eval-and-trace tool.
Numbers that earn their color
Confidence intervals on every comparison, anytime-valid, plus advanced Bayesian, CUPED, and SRM detection, and an explicit "no data" state instead of a fabricated zero. A 2% move never gets to masquerade as signal.
Failures become your next evals
Root-cause a failing production cluster, then promote it (human-gated, with a corrected answer) straight into the golden set, so the eval library keeps compounding.
Whole-trajectory metrics
Trajectory efficiency, redundancy, tool-use and step-reasoning accuracy, measured as eval criteria with a CI on the offline-to-online delta, and traffic separated by human vs agentic vs bot origin.
Pricing side-by-side
Winnow Pro
$99/seat/mo
Free: $0, 5M runs/mo, 3 agent second opinions/mo
- Evals, experiments, gates, guardrails, bandits
- 50 agent second opinions/mo · standard depth
- 25M runs/mo · 100M on Team
- Self-hosted option on Enterprise
Braintrust Pro
$249/seat/mo
Free: 1M traces/mo
- LLM eval + observability
- Playground with grid compare
- Brainstore trace storage
- No online experiments or gates
Honest positioning
Pick Winnow when
- You need real online experiments with p-values and confidence intervals
- Feature gates, bandits, or guardrails are part of how you ship
- You want an agent that reasons about whether to ship, with refutation conditions
- Self-hosting is on the table
- $249/seat is more than the budget allows
Pick Braintrust when
- Pure LLM eval and tracing is the whole job
- The Playground grid is a critical authoring surface for your team
- Brainstore trace query latency is load-bearing for your workflow
- You are not running online A/B tests and do not plan to
Start with eval. Close the loop when you are ready.
The Free tier covers 5M runs/mo and includes 3 agent second opinions so you can try the reasoning surface before upgrading.