Braintrust delivers an elegant dev playground for AI development. Arize offers two complementary platforms that mirror Braintrust’s dev-speed while also adding muscle in several areas.
Key Differences
Self-Hosting & Cost
Key differences with self-hosting and cost:
- Arize Phoenix: one-command Docker, no usage caps.
- Arize AX: single-tenant VPC or on-prem with 99.9 % SLA
- Braintrust: “hybrid” Enterprise deployment—UI/control plane stays SaaS while customers run Brainstore and API servers, plus seat/eval/retention fees and a capped free tier (1 M spans, 10 k scores, 14-day retention)
Instrumentation & Agent Support
Phoenix’s OpenInference auto-instruments popular frameworks, producing OTel spans for every tool call and agent step in sub-second latency. Braintrust accepts OTel but supplies no semantic conventions or auto-instrumentors, so developers embed its SDK/proxy manually. Both Phoenix and Arize AX also visualize multi-agent graphs, session flows and token & cost tracking.
Evaluation Workflows
Phoenix/AX benchmark evaluators against labeled “golden” datasets and can auto-score tens of millions of outputs daily with full logs for failure debugging. While Braintrust offers online-eval sampling/logs, it does not offer an OSS eval framework or benchmarking.
Production Monitoring & Insights
Arize AX augments Phoenix’s basics with custom dashboards, alert rules, Slack/PagerDuty routing, and AI Copilot insight discovery. Braintrust ships none of these; teams must refresh the UI manually.
Human-In-the-Loop
Both Arize AX and Phoenix include annotation queues that attach ratings or corrected answers to live or historical traces, then automatically recompute metrics. Braintrust has a manual Review screen and no queueing or reconciliation.
Enterprise Readiness & Scale
Arize AX adds HIPAA, ISO 27001, SOC-2 Type II, SAML/SSO, audit logs, VPC/on-prem options, and petabyte storage – on a platform architected for scale. Braintrust lists SOC-2 but not HIPAA and is run by ~30 staff.
Feature Comparison
| Capability | Phoenix (OSS) | Arize AX | Braintrust |
| Open source code | ✅ | – | ❌ |
| One-click Docker deploy | ✅ | ✅ | ❌ (hybrid) |
| Agent tracing | ✅ | ✅ | ❌ |
| Agent graphs | ✅ | ✅ | ❌ |
| Multi-agent session view | ✅ | ✅ | ❌ |
| Token & cost tracking | ✅ | ✅ | ✅ |
| Auto-instrumentation (OpenInference) | ✅ | ✅ | ❌ |
| Multi-modal spans | ✅ | ✅ | ✅ |
| Custom metrics builder | ✅ | ✅ | ❌ |
| Copilot AI insights | ❌ | ✅ full | ❌ |
| Dashboards & alerts | 🔸 | ✅ | ❌ |
| Annotation queues | ✅ | ✅ | ❌ |
| Offline evals | ✅ | ✅ | ✅ |
| Online evals (millions/day) | ✅ | ✅ | ⚠️ logs |
| Bias tracing / explainability | ✅ | ✅ | ❌ |
| AI trace search / cohort slicing | 🔸 | ✅ | ❌ |
| Data export & DB sync | UI & SDK | Unlimited + Arize DB | ✅ |
| SSO / RBAC / Audit | – | ✅ | SOC-2 only |
| HIPAA, VPC / on-prem | – | ✅ | ❌ |
| Pricing | Free | Usage-based (no seat/eval tax) | Seat + eval + retention fees |
How To Choose
- Startups & fast prototypers → Spin up Phoenix for free, keep your data local, enjoy open-standard spans, built-in evals, and basic dashboards.
- Growth-stage, enterprises and regulated orgs → Flip the switch to Arize AX for petabyte scale, HIPAA, audit trails, and Copilot-powered insights—without rewiring instrumentation.
- Braintrust users will love its agent playground and slick UI, but may run into headaches if they need annotation queues, automated alerts, or enterprise controls.