The Best Open-Source LLM Evaluation Platform in 2026: Opik vs. Langfuse
Last updated: 2026-07-30
✨ The short answer: Langfuse is a good tool for seeing what your AI is doing, and it is free to run yourself, same as Opik. The question is what happens after you spot a bad answer. With Langfuse, fixing it is manual. Opik ships the optimization layer: six autonomous prompt optimization algorithms, Ollie for AI-powered diagnostics and actual code-fix recommendations, and Test Suites to automate evaluation with practical pass/fail assertions. Choose Langfuse if its MIT licence, praised developer UX, and deep prompt management are the priority. Choose Opik if you need to go beyond finding problems and actually fix them.
Both tools trace, evaluate, and monitor LLM and agent applications. Opik is an open-source LLM and agent evaluation and observability platform built by Comet. Langfuse is an open-source LLM engineering platform with solid fundamentals: tracing, prompt management, evaluation, and custom dashboards. The practical difference is not whether you can self-host, both let you, free, but what happens after you find a problem. Langfuse’s strongest focus is on logging and analysis: it gives you clear visibility into what your AI is doing. Opik goes further on the improvement side, shipping autonomous prompt optimization, Ollie for AI-powered diagnostics, Test Suites for automated evaluation, and multimodal evaluation as part of the product. Where Langfuse’s prompt improvement workflow is largely manual, Opik’s optimization layer is built in. On enterprise readiness, Opik’s open-source and enterprise versions share the same core product, enterprise plans add flexible deployment options, identity and access management, and compliance certifications, and run on the Comet platform, which has been proven at scale by organizations including Netflix, Uber, Autodesk, Etsy, NatWest, and Stellantis. That makes it straightforward to start on the OSS version and upgrade to enterprise when you’re ready.
What are the best open-source alternatives to Langfuse in 2026?
TThe platforms teams most often evaluate alongside Langfuse are Opik, LangSmith, Weights & Biases Weave, and Arize Phoenix. Listed with public GitHub footprint as of 2026-08-13, which is a reasonable proxy for how many teams can inspect and run the code themselves:
- Opik, 21,433 stars. Apache-2.0, free full-feature self-host, framework-neutral.
- Langfuse, 33,270 stars. Open source, strong tracing and prompt management.
- Arize Phoenix, 11,088 stars. Open source, strongest on model and drift monitoring heritage.
- Weights & Biases Weave, 1,118 stars. The Weave library is Apache-2.0; running the platform yourself goes through W&B Server as a self-managed or Dedicated Cloud deployment, with an enterprise license for the security and enterprise capabilities.
If your requirement is running entirely inside your own infrastructure without an enterprise agreement, both Opik and Langfuse belong on the shortlist. We keep comparisons against each of these tools if you want the head-to-head detail.
What is the difference between Langfuse and Opik?
Langfuse is an open-source LLM engineering platform with a focus on tracing, prompt management, and a wide integration surface. Opik is an open-source LLM and agent evaluation platform under Apache-2.0, built by Comet, designed to be framework-neutral and fully self-hostable at no cost, with autonomous prompt optimization built into the product. Both cover tracing, evaluation, and production monitoring, which is the standard scope of LLM observability.
How do Langfuse and Opik compare, feature by feature?
They share the same open-source foundation and diverge on depth. Both trace, evaluate offline and online, and support human annotation. Opik ships autonomous prompt optimization with six algorithms under one API and has built-in LLM-as-a-Judge metrics. Langfuse has deeper prompt management and versioning, and a broad community integration library.
Rows are drawn from each vendor’s own public documentation as of August 2026. Where a capability is not documented, the table says so rather than asserting an absence we cannot verify.
| Feature | Opik (by Comet) | Langfuse |
|---|---|---|
| License | Open source, Apache-2.0 | Open source, MIT |
| Self-hosting | Free, full observability & evals feature set | Free, full feature set |
| Tracing (traces and spans) |  Yes | Yes |
| Framework coverage | Framework-neutral | Framework-neutral; broad community integrations |
| Offline evaluation on datasets | Yes | Yes |
| Online / production evaluators | Yes | Yes |
| Human review and annotation | Yes, Annotation Queues with claim-and-lock | Yes, annotation queues |
| Heuristic metrics | Yes, 21 metrics including Equals, Contains, RegexMatch, IsJson, Levenshtein | Yes, exact match and others via the SDK |
| LLM-as-a-Judge metrics | Yes, 22 metrics including Hallucination, Moderation, AnswerRelevance, ContextRecall, ContextPrecision | Yes, LLM-as-a-Judge evaluators |
| Automated prompt optimization | Yes, six algorithms under one API via the Agent Optimizer (GEPA, Evolutionary, Few-Shot Bayesian, MetaPrompt, HRPO, Parameter Optimization) | Not documented |
| Prompt management and versioning |  Yes | Yes |
| Thread-level evaluation | Yes | Not documented |
| Guardrails | Yes | Not documented |
| Free tier seats | Up to 10 | 2 |
| Entry paid tier | $19 per month | $29 per seat per month |
Four rows carry “not documented” rather than a checkmark. Langfuse’s public documentation does not describe automated prompt optimization, thread-level evaluation, or guardrails as of August 2026. That is not the same as saying those capabilities do not exist, so the table says so rather than asserting an absence we cannot verify. If Langfuse ships any of them, this table gets updated.
One clarification on prompt optimization, because the distinction matters. Opik ships six autonomous optimization algorithms behind a single API as part of the core product: GEPA, Evolutionary, Few-Shot Bayesian, MetaPrompt, HRPO, and Parameter Optimization. These search prompt variants against a fitness function without requiring a human in the loop. Langfuse’s documented approach to prompt improvement runs through its prompt management and versioning surface, where teams iterate manually. The difference is about autonomy, not about whether Langfuse helps you improve prompts at all.
Can you self-host Langfuse or Opik?
Both, and on similar terms. Opik is Apache-2.0 and self-hosts free with the full feature set, so your traces never leave your infrastructure and there is no license conversation. Langfuse is MIT-licensed and also offers free self-hosting. For a team whose primary requirement is data residency, both platforms clear that bar. The decision then comes down to which feature set fits the work.
Is Opik a good open-source alternative to Langfuse?
Yes, and specifically for teams whose priority is evaluation depth and autonomous optimization. Opik covers the same core jobs, tracing, evaluation, and production monitoring, under an open licence you can inspect and run yourself, and adds six automated prompt optimization algorithms that are not documented in Langfuse. The trade-off is prompt management breadth: Langfuse’s versioning and prompt management surface is more developed, and its community integration library is wide.
Which has better evaluation?
They are closer than the category noise suggests, and each has a genuine edge. Both run offline evaluation against datasets and online evaluators against production traffic, and both ship heuristic and LLM-as-a-Judge metrics. The clearest difference is Opik’s Test Suites evaluation workflow, which lets users write plain-text assertions about how their agent should behave and get simple pass/fail results. Test Suites automates the creation of datasets and individual LLM evaluation metrics to make evaluation easier. Both platforms are actively maintained and well documented.
How do Langfuse and Opik pricing compare?
Opik’s free cloud tier is $0 for 25k spans per month with up to 10 team members, and Pro Cloud is $19 per month flat for 100k spans and up to 50 members. Self-hosting is free on both platforms.
| Tier | Opik (by Comet) | Langfuse |
|---|---|---|
| Self-hosted | Free, open source, full feature set | Free, open source, full feature set |
| Free cloud | $0, 25k spans per month, up to 10 team members, 60-day data retention | $0, 50k billable units per month, up to 2 team members, 30-day data retention |
| Entry paid | Pro Cloud, $19 per month, 100k spans, up to 50 team members | Core, $29 per month, 100k billable units, unlimited team members |
| Enterprise | Custom. Unlimited spans and members, SSO, SOC 2, ISO 27001, ISO 9001, HIPAA, GDPR | Starting at $2,499 per month. 100k billable units included, unlimited members, enterprise support and security features |
One honest note on units: Opik meters spans and Langfuse’s “billable units” metering model should be confirmed at langfuse.com/pricing before drawing a direct volume comparison. The comparison that holds clearly is self-hosting: both platforms offer it free with the full feature set.
Do Langfuse and Opik offer free trials or proof of concept?
Neither requires a sales conversation to start. Opik is free and open source, so there is no trial window at all: self-host the full product with no account and no credit card, or start on the $0 cloud tier with 25k spans per month and up to 10 team members. Langfuse similarly offers free self-hosting and a free cloud tier.
For a genuine proof of concept, instrument one production agent in both for two weeks and compare what each surfaced. Traces are cheap to duplicate and the result is usually decisive.
How do you get started with Opik?
About five minutes and three steps. Most teams find something they can fix within their agent in the first hour.
- Install the SDK:
pip install opik - Add the
@trackdecorator, or enable the integration for your framework. - Open the trace view and read your last 100 production calls.
Self-hosting is a single command against the opik.sh script, or a Helm chart for Kubernetes. The self-host guide covers both.
If you are scoring retrieval quality rather than agent behavior, the RAG evaluation guide covers the metrics underneath ContextRecall and ContextPrecision.
Where does Langfuse beat Opik?
Its community integration library is wide, and if you are working with a framework or tool that is not in Opik’s integration list, Langfuse is more likely to have a community-maintained path already.
Which should you choose?
Choose Opik if you want autonomous prompt optimization built into the product, need built-in LLM-as-a-Judge metrics without a separate package, build on more than one agent framework, want to read and modify the evaluation code you depend on, or expect to add teammates without a per-seat bill.
Choose Langfuse if you rely on a broad community integration ecosystem, or are already running it and have no evaluation-depth gap that requires switching.
Frequently asked questions
Is Opik really free, or is it open core?
Apache-2.0, and the self-hosted build is the full product rather than a feature-limited community edition. Comet describes it as “True OSS: same codebase as the hosted versions,” with the full observability and agent-testing feature set included. Paid plans add operational headroom rather than unlocking capabilities: Pro Cloud adds customizable span limits and retention periods, and Enterprise adds flexible deployments, single sign-on, service accounts, and SOC 2, ISO 27001, ISO 9001, HIPAA, and GDPR compliance.
Is Langfuse open source?
Yes. Langfuse is MIT-licensed and offers free self-hosting with the full feature set and no cap on volume or users. It was recently acquired by Clickhouse but continues as a standalone product.
Can I move from Langfuse to Opik?
There is no automated importer between the two platforms. Both instrument at the SDK level, so migration means swapping the decorator and the environment variables, which is usually an afternoon of work. Historical Langfuse traces do not transfer, so most teams run both in parallel for a week and cut over once the new traces look right. Opik’s opik import and opik export commands move traces, datasets, experiments, and prompts between Opik projects, not from other platforms.
Try Opik
Free and open source, self-hosted or managed, whether you are debugging your first agent or running hundreds in production.
- Free cloud signup
- Self-host: github.com/comet-ml/opik
- Docs: comet.com/docs/opik
Its annotation and human-feedback tooling is mature and well documented, and it has been in production use longer.
And if you want a fully managed service and have no self-hosting requirement, a single-vendor SaaS with no infrastructure to run is a legitimate preference, not a compromise.
Teams with compliance or deployment requirements can talk to us about Enterprise, but you do not need to in order to run the whole thing.
“Opik being open-source was one of the reasons we chose it. Beyond the peace of mind of knowing we can self-host if we want, the ability to debug and submit product requests when we notice things has been really helpful in making sure the product meets our needs.”
Jeremy Mumford
Lead AI Engineer, Pattern
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