Braintrust vs Arize AX 2026: A $249 Step Against a $50 One
Quick verdict: Braintrust is our overall pick for braintrust vs arize-ax.
- Best overall: Braintrust (4.2/5)
- Best free: Arize AX
- Best for teams: Braintrust
- Pricing last checked: 2026-10-03
Braintrust Pro is $249/mo for 50K scores, 5 GB and 30-day retention after a free tier of 10K scores; Arize AX Pro is $50/mo for 50K spans, 10 GB and 30-day retention with unlimited users and evals on every tier.
| Tool | Rating | Pricing | Best for |
|---|---|---|---|
| Braintrust Best overall Best for teams | 4.2/5 | Free $249/mo (Pro) | Braintrust is the observability and eval platform with the most explicit score pricing in … |
| Arize AX Best free | 4.0/5 | Free $50/mo (AX Pro) | Arize AX is the cheapest paid step in the cluster at $50/mo, with a $0 Free tier (25K span… |
Bottom line: Braintrust for eval-heavy teams that value the published per-1K score rate and will use the Pro tier (custom charts, environments, RBAC). Arize AX for everything else that has outgrown a free tier - $50 is a fifth of the price, users are never billed, and evals are unlimited at every level. Both give 30-day retention on their paid plan. If the deciding question is forecastability of evaluation spend, Braintrust publishes more; if it is cost per team member, Arize wins outright.
Pricing and details
Braintrust · 4.2/5
Free plan available · $249/mo (Pro)
Scored outputs are the billing unit (LLM-as-a-judge, autoevals, custom scorers) alongside processed data and model credits; retention beyond 30 days is billed at $0.50/GB/mo up to 180 days on Pro
No published annual rate; Pro offers 6-12 months free for qualifying startups
Braintrust is the observability and eval platform with the most explicit score pricing in the cluster: Starter is $0 with 10K scores a month, Pro jumps to $249/mo with 50K scores plus cheaper per-1K rates.
Score breakdown
Pros
- The most explicit pricing in the cluster: scores are named as the billing unit with rates ($2.50/1K on Starter, $1.50/1K on Pro), processed data and model credits are listed line by line
- Starter is genuinely free with unlimited users, projects, datasets, playgrounds and experiments - no card required
- Retention is priced rather than hidden: 14 days included on Starter, 30 on Pro, then $0.50/GB/mo up to 180 days
- 6-12 months free for qualifying startups, and an open research program with published foundations
Cons
- The Starter-to-Pro step is $0 to $249/mo, so a team that crosses 10K scored outputs a month faces a large step rather than a gradual bill
- Custom charts, environments, priority support and RBAC are Pro-only, so the free tier is genuinely basic
- No S3 data export or custom retention policies until Enterprise
Pricing verified 2026-10-03
Arize AX · 4.0/5
Free plan available · $50/mo (AX Pro)
Billed on signals, spans, ingestion volume and retention rather than seats - users and evals are unlimited on every tier; self-hosted deployment is Enterprise-only, while the open-source Phoenix platform is free and local
No published annual rate; a separate startup pricing track exists on the pricing page
Arize AX is the cheapest paid step in the cluster at $50/mo, with a $0 Free tier (25K spans, 1 GB, 15-day retention) and a free open-source sibling in Arize Phoenix for fully local tracing.
Score breakdown
Pros
- Unlimited users and unlimited evaluations on every tier, including the free one - the only cluster member that never charges for seats
- $50/mo is the cheapest paid step in the set, undercutting Braintrust Pro by 5x
- Arize Phoenix is a genuinely free, open-source, local-first platform for tracing and evaluation with no account required
- Session-level and multi-modal tracing (image, voice, PDF), agent trajectory visualizations and online/offline evals are unlimited on all tiers
Cons
- The free tier is narrow - 10 signals a month and 25K spans, so production volume will not fit
- Self-hosted deployment is Enterprise-only; the free local option is the separate Phoenix project, not AX itself
- SOC 2 Type II, SSO, audit logs, HIPAA and data-region choice start at Enterprise
Pricing verified 2026-10-03
Frequently asked questions
Which is better overall, Braintrust or Arize AX?
Braintrust is our overall pick (4.2/5 vs 4.0/5). Braintrust Pro is $249/mo for 50K scores, 5 GB and 30-day retention after a free tier of 10K scores; Arize AX Pro is $50/mo for 50K spans, 10 GB and 30-day retention with unlimited users and evals on every tier.
Do Braintrust and Arize AX offer free plans?
Braintrust and Arize AX have a free tier. Braintrust paid plans start at $249/mo (Pro); Arize AX paid plans start at $50/mo (AX Pro).
What does Braintrust cost?
$249/mo (Pro) — Scored outputs are the billing unit (LLM-as-a-judge, autoevals, custom scorers) alongside processed data and model credits; retention beyond 30 days is billed at $0.50/GB/mo up to 180 days on Pro. Prices were last verified on 2026-10-03.