Opik vs Langfuse in 2026 - The Two Open-Source Defaults, Compared

Opik and Langfuse are the two tools that come up when someone wants open-source LLM observability that does not cripple you when you self-host. Both are permissive-licensed. Both do tracing, evals and prompt management. Both let you run the real product on your own infrastructure for free. So the honest question is not “which is open source” - it is which one fits your budget, your ops capacity and your appetite for a newer tool. Opik is cheaper on the cloud and simpler to self-host at full features. Langfuse has the longer track record and the bigger install base. I have added Braintrust as the third option, because if evals are your actual center of gravity, neither of these is the most turnkey answer.

The short version

Tool	Best for	Cloud starting price	Self-host / license
Opik	Cheapest managed cloud, simplest full self-host	$19/mo (100k spans)	Free, Apache-2.0, full features
Langfuse	The established open-source default	$29/mo (100k units)	Free, MIT, near-complete
Braintrust	Turnkey evals and CI regression gates	$249/mo	Hybrid, Enterprise only

Opik: cheaper cloud, cleaner self-host

Opik is Comet’s open-source observability and eval platform, and it competes on terms. Its OSS build is Apache-2.0 with the full feature set self-hosted - unlimited spans, members and retention, no gates - and it is designed to self-host at Kubernetes scale without losing features. That is fewer moving parts than Langfuse’s four-service stack, which matters if your ops budget is thin.

On the cloud, Pro is $19/mo for 100k spans, the cheapest paid cloud of the major platforms, with $5 per additional 100k. The free cloud tier gives you 25k spans, up to 10 members and 60-day retention. It ships 60+ framework integrations, LLM-as-judge, code metrics, guardrails and an Agent Optimizer, and it is the fastest-growing project of its peers at roughly 20.8k GitHub stars. Comet has been around since 2017, so this is not a solo side project.

The gotcha is per-seat pricing at scale. The $19 headline is the small-team configuration, and the recurring complaint is that seat costs climb as the team grows. A few users report UI slowdown on very large projects, and cloud retention defaults to 60 days - longer costs extra. None of that undercuts the core value, but model the seat cost if you are a big team.

Langfuse: the established default with the ops tax

Langfuse is the tool most people already mean when they say “open-source observability.” It is MIT-licensed, and self-hosting is free with only three features enterprise-gated - tracing, evals, prompt management, human annotation and RBAC are all included. It runs about $101/mo managed at 1M events, and Core is $29/mo for 100k billable units with 90-day retention, a touch more than Opik’s cloud but with longer default retention.

The track record is the real argument for it. Langfuse was founded in 2022 in Berlin, went through YC W23, and had over 2,000 paying customers and 19 of the Fortune 50 using it at acquisition. If you want the tool with the deepest install base, this is it.

The catch is operational. Langfuse v3 moved to Postgres plus ClickHouse, Redis and S3-compatible storage - four services - and the migration is where self-hosters get stuck, with GitHub threads reporting memory errors and timeouts. Its OTLP support is HTTP only, no gRPC yet. And it is now a ClickHouse subsidiary after the January 2026 acquisition, which I would weigh for a multi-year bet. The Langfuse page walks through it.

Braintrust: if evals are the actual point

Both Opik and Langfuse do evals, but if regression testing is your center of gravity, Braintrust is more turnkey out of the box. Its autoevals library ships working scorers, and its CI/CD quality gates can block a merge on a statistically significant regression - not just log that quality dropped. Human review, automated scorers, tracing and datasets share one system, and there is no per-seat charge.

The trade-offs are real. Billing meters “processed data” in GB, counting every byte, with no hard spending cap, and the $0 Starter jumps straight to $249/mo. Self-host is hybrid-VPC only and Enterprise-only, and the Brainstore backend is closed - so it is not the free, open self-host that Opik and Langfuse both offer. Set up billing alerts on day one if you go this way.

Opik vs Langfuse: which should you pick?

• You want the cheapest managed cloud - Opik at $19/mo, ahead of Langfuse Core at $29/mo.
• You want the simplest full-featured self-host - Opik, which self-hosts the whole product without a four-service stack.
• You want the tool with the deepest track record and biggest install base - Langfuse, with over 2,000 paying customers and 19 of the Fortune 50.
• You are a large team sensitive to per-seat cloud pricing - model both, but Langfuse’s unlimited-users cloud tiers may age better than Opik’s per-seat model.
• Regression testing and CI gates are the real job - Braintrust, with billing alerts on from day one.

The honest truth is that both Opik and Langfuse are excellent, and you will not regret either. If budget and self-host simplicity lead, go Opik. If track record and install base lead, go Langfuse. If evals are the whole reason you are shopping, look at Braintrust before you commit to either. Every price and date here was read from each vendor’s own materials, verified on 26 July 2026, and this category ships breaking changes monthly, so we re-verify every 30 days.