Langfuse

Langfuse covers the full LLM engineering loop — tracing/observability, prompt versioning and a playground, datasets, and both offline (SDK/UI) and online (LLM-as-judge) evaluation — as one integrated product rather than a bundle of point tools. Instrumentation is framework-agnostic: native OpenTelemetry ingestion plus SDKs for Python and JavaScript, so it isn't tied to LangChain the way LangSmith is (https://langfuse.com/docs/opentelemetry/get-started, https://langfuse.com/docs/observability/sdk/overview). The core (everything outside the ee/ directories) is MIT-licensed and the self-hosted Open Source tier has no usage caps or feature gates on the core observability/eval/prompt features — you can run the whole non-enterprise product on Docker Compose or Kubernetes for free (https://langfuse.com/pricing-self-host, https://raw.githubusercontent.com/langfuse/langfuse/main/LICENSE). Cloud pricing is usage-based (billed per ingested trace/observation/score, a "unit"), not per-seat, so adding engineers to a team doesn't move the bill — a real structural difference from seat-billed competitors like LangSmith. The project is large and active: 33,767 GitHub stars, 3,649 forks, and releases shipping multiple times a week (v4.21.0 and v3.225.5 both cut on 2026-08-26) (https://api.github.com/repos/langfuse/langfuse, https://github.com/langfuse/langfuse/releases).

Langfuse is no longer an independent company. ClickHouse acquired it on 2026-01-16, alongside a $400M Series D funding round for ClickHouse led by Dragoneer Investment Group (https://clickhouse.com/blog/clickhouse-acquires-langfuse-open-source-llm-observability, https://clickhouse.com/blog/202602-newsletter). In Langfuse's own announcement, the founders say the deal came together while they had term sheets in hand for a Series A, and frame it as continuity: "no planned changes to licensing," "Langfuse Cloud keeps running as-is," and "the whole Langfuse team will join ClickHouse to continue building Langfuse" (https://langfuse.com/blog/joining-clickhouse) — this is the vendor's own characterization, not independently verified. The GitHub repo's copyright line now reads "Copyright (c) 2023-2026 ClickHouse, Inc." (https://raw.githubusercontent.com/langfuse/langfuse/main/LICENSE). Independent commentary eight months post-close (an OpenObserve competitor comparison, so read with that in mind) corroborates that the practical outcome so far has been unremarkable: MIT core intact, self-hosting still works at production scale, Cloud endpoints unchanged (https://openobserve.ai/blog/langsmith-alternatives/). For a buyer, the relevant question isn't whether this was handled well — it was — but that Langfuse's roadmap now answers to ClickHouse rather than to an independent board, which matters on a multi-year horizon even though nothing has changed operationally yet.

Cloud: free Hobby tier (50k billable units/month, 2 users, 30-day data retention, no card required); Core at $29/month (100k units included, unlimited users, 90-day retention); Pro at $199/month (3-year retention, SOC2/ISO27001 reports, HIPAA BAA available, plus an optional $300/month Teams add-on for SSO/RBAC); Enterprise at $2,499/month (audit logs, SCIM, custom rate limits, uptime SLA). Additional usage beyond included units is graduated: $8/100k units from 100k–1M, dropping to $6/100k above 50M (https://langfuse.com/pricing). A "unit" is any trace, observation (span/event/generation), or score ingested — worth modeling against your actual trace volume before comparing sticker prices, since a chatty agent can rack up units fast. Self-hosting is free and unlimited on the Open Source (MIT) tier; the Self-Hosted Enterprise tier is custom-priced, bundled with a ClickHouse Cloud/BYOC commercial plan, and is what actually unlocks project-level RBAC, data retention policies, audit logs and SOC2/ISO27001 reports when self-hosting (https://langfuse.com/pricing-self-host) — so a security-conscious team that wants to self-host AND get compliance reports ends up paying either way.

The repository license is MIT for everything outside ee/, web/src/ee/, and worker/src/ee/; those directories carry a separate Langfuse/ClickHouse Enterprise License that forbids copying, merging, publishing, distributing, sublicensing or selling without a paid Enterprise License, though you may modify and run it for development/testing without a subscription (https://raw.githubusercontent.com/langfuse/langfuse/main/ee/LICENSE). GitHub reports the repo's overall license as "Other/NOASSERTION" rather than a clean MIT badge, for exactly this reason (https://api.github.com/repos/langfuse/langfuse — license.spdx_id: NOASSERTION). In practice this means: tracing, evaluation, prompt management and datasets are all free and self-hostable; enterprise SSO enforcement, project-level RBAC, SCIM, audit logs and server-side data masking are gated behind either the Pro/Teams-and-up Cloud tiers or a paid Self-Hosted Enterprise license (https://langfuse.com/pricing-self-host).

Langfuse publishes a public status page with incident history (https://status.langfuse.com/history). Looking at May–August 2026: incidents are frequent but consistently minor and short — mostly ingestion/evaluation latency degradations and delayed processing in specific regions, each resolved same-day, plus one broader ClickHouse Cloud infrastructure incident on 2026-07-01 that Langfuse's own status page links out to (https://statuspage.incident.io/clickhousecloud/incidents/01KT1G25S9PBKM7VJEB146680G). There's no record of extended outages or data loss in that window. This is a reasonable trail for a data-intensive ingestion product, but note it reflects Cloud only — self-hosted deployments carry their own operational risk that this page says nothing about.

Founded by Marc Klingen, Clemens Rawert and Max Deichmann, who built Langfuse during Y Combinator's W23 batch starting from a self-hosted Postgres-backed tool and rearchitected onto ClickHouse for v3 as usage grew (https://www.ycombinator.com/companies/langfuse, https://langfuse.com/blog/joining-clickhouse). As of January 2026 the team joined ClickHouse as part of the acquisition rather than remaining a standalone company; headcount and any changes since are not established from public sources.