Opik vs Braintrust in 2026 - Cheapest Open Source vs Best Turnkey Evals

Opik and Braintrust get compared a lot because they answer the same broad need - score whether your LLM app is any good, and catch it when it gets worse. But they come at it from opposite ends. Opik leads with open source and low cost. Braintrust leads with turnkey regression testing. One is the cheapest, most permissive option in the category; the other is the most complete eval workflow out of the box, with a billing model you have to watch. Neither is strictly better - it depends on what you are optimizing for. I have added Langfuse as the third reference point, because it is the open-source default a lot of teams end up on.

The short version

Tool	Best for	Self-host	License	Starting price
Opik	Cheapest managed cloud, permissive OSS	Full, no gates	Apache-2.0	Free / $19/mo
Braintrust	Turnkey evals and CI regression gates	Hybrid, Enterprise only	SDKs open, backend closed	Free / $249/mo
Langfuse	Open-source observability default	Full, free	MIT	Free / $29/mo

Opik: open source without the asterisk, and the cheapest cloud

Opik is Comet’s open-source observability and eval platform. It captures multi-step traces - LLM calls, tool executions, agent activity - and layers on datasets, experiments, LLM-as-judge and code-based metrics, online evaluation, Guardrails and an Agent Optimizer. But the reason to pick it is not any single feature. It is the terms. Opik’s OSS build is Apache-2.0, and Comet states the self-hosted version ships the full feature set with unlimited spans, members and retention, and no feature gates. That is the most permissive license in this set - more so than Phoenix’s Elastic License.

On the cloud, the number that matters: Pro is $19/mo for 100k spans, the cheapest paid tier of the major eval platforms, with $5 per additional 100k. The free cloud tier gives you 25k spans, up to 10 members and 60-day retention. Opik is also the fastest-growing project of its peers, at roughly 20.8k GitHub stars, and it is backed by Comet, an established ML-platform company since 2017 with about $63M raised.

The honest gotcha is per-seat pricing at scale. The $19 headline is the small-team configuration. The recurring complaint is that seat costs climb as your team grows, and a few users report UI slowdown on very large projects. Neither undercuts the core value, but a big team should model the seat cost first. Opik also treats OpenTelemetry as one ingestion path among 60+ integrations, not the native architecture - fine for most stacks, worth knowing if you are standardizing strictly on OTel.

Braintrust: the most turnkey regression testing, watch the meter

Braintrust started with evals and built observability around them, and it shows. Most tools in this category are observability-first with evals bolted on. Braintrust is the reverse, and it is the one platform where human review, automated scorers, LLM-as-judge, tracing and datasets share one system wired to your test pipeline. The autoevals library ships working scorers out of the box - exact match, embedding similarity, LLM-as-judge factuality - and the CI/CD quality gates can block a merge when a change causes a statistically significant regression. Not just log that quality dropped - actually stop the bad code from shipping. There is no per-seat charge either; users are unlimited on every tier. It is well funded, with an $80M Series B led by Iconiq in February 2026 at a roughly $800M valuation.

The gotcha is the billing meter. Braintrust bills “processed data” in GB, counting every byte of inputs, outputs, prompts, metadata, traces and spans, and there is no hard spending cap. The $0 Starter jumps straight to $249/mo with nothing in between. And the meter punishes exactly the workloads that most need observability - verbose multi-step agents and big RAG contexts burn the GB allowance fastest. Self-hosting is not an escape hatch either: it is a hybrid, Enterprise-only arrangement where the Brainstore backend stays closed. Set up billing alerts on day one, or the $249 plan will not stay $249.

Langfuse: the open-source middle ground

If Opik’s appeal is openness and Braintrust’s is turnkey evals, Langfuse is where a lot of teams land as the general-purpose open-source default. It is MIT-licensed and self-hosts free with only three features enterprise-gated, it is framework-agnostic, and at 1M events a month it runs about $101/mo managed. The trade-off versus Braintrust is that for full regression testing you assemble more of the orchestration yourself - Braintrust hands you that orchestration ready-made. The trade-off versus Opik is mostly license flavor and the four-service self-host stack (Postgres plus ClickHouse, Redis and S3). If your center of gravity is observability with evals attached rather than evals-first, Langfuse is the safer default.

Opik vs Braintrust: which should you pick?

• Regression testing and blocking bad merges is the whole point - Braintrust, with billing alerts on from day one. Nothing else here is this turnkey for CI quality gates.
• You want open source that actually means open source, self-hosted with every feature - Opik under Apache-2.0, no gates.
• You want the cheapest managed cloud - Opik at $19/mo, an order of magnitude under Braintrust’s $249 floor. Just model the per-seat cost if your team is large.
• You run verbose agents or big RAG contexts on a tight budget - avoid Braintrust’s uncapped byte meter; Opik’s span-based pricing or Langfuse self-host is more predictable.
• You want a general open-source observability platform with evals attached - Langfuse, if you can run the four-service self-host.

The honest summary: Braintrust is the better tool if evals and CI gates are your job and you will watch the meter. Opik is the better deal if openness and cost drive the decision - permissive license, full-featured self-host, cheapest cloud. Both are genuinely good; they are just optimized for different buyers. Pick the axis that matters most to you and the answer falls out.

Every price and date here was read from each vendor’s own materials and verified on 26 July 2026. This category ships breaking changes monthly, so we re-verify every 30 days.