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Fiddler AI vs Langfuse

Two fact sheets from our own research, side by side — pricing, platforms, API access and status re-checked by us rather than quoted from the vendors.

The short answer

Free plan
Both have one
Public API
Both have one
Higher Trust score
Fiddler AI — 90 vs 80 for Langfuse
Best fit
Fiddler AI: Enterprises needing audit trails and governance over AI agents in regulated industries · Langfuse: Engineering teams running LLM apps or agents in production who need traces and cost tracking
Status
Both up at our last check — Fiddler AI Oct 15, 2026, Langfuse Oct 29, 2026

From our own records as of each tool's last check. Anything we have not confirmed is left out rather than guessed. How we verify

Fiddler AIEnterprise control plane for AI: guardrails, observability and governance for LLM agents and ML modelsLangfuseOpen-source LLM engineering platform for tracing agents, versioning prompts, running evals and tracking cost, hosted or self-hosted.

Side by side

FactFiddler AILangfuse
CategoryLLM Observability & EvaluationLLM Observability & Evaluation
Pricing modelFreemiumFreemium
Starts at—$29/mo
Public APIYesYes
Trust score90 / 10080 / 100
PlatformsWeb, APIWeb, API
CompanyFiddler AILangfuse GmbH
Launched20182023
Last verifiedOct 15, 2026Oct 29, 2026

What our research says

Fiddler AI

One of the longer-standing model-monitoring vendors, rebuilt around agent observability and inline guardrails with credible enterprise deployment options. Self-serve depth is limited: the free tier is guardrails-only and anything serious routes through the sales motion.

Pros

  • Guardrails run on its own models without external LLM API calls, keeping latency and data exposure down
  • Covers classic ML monitoring and agentic tracing in one platform
  • Deployment options include SaaS, VPC, GovCloud and on-premises
  • Named enterprise customers such as Mastercard and the U.S. Navy

Cons

  • Per-trace pricing makes high-volume costs hard to predict without modeling
  • Most differentiating capabilities sit behind the Enterprise tier

Langfuse

Langfuse is a strong default for teams that want tracing, prompt versioning and evaluations in one open-source tool, with the option to keep data on their own infrastructure. Teams that only want a hosted logging proxy with no SDK work, or that need guaranteed enterprise SSO without paying for add-ons, may find simpler or more bundled options.

Pros

  • MIT-licensed core that can be self-hosted without usage limits
  • Covers tracing, prompt management, evaluation and dashboards in one product
  • Generous free cloud tier and unlimited users from the $29 Core plan
  • OpenTelemetry support and SDKs for Python and JavaScript

Cons

  • Usage above the included 100k units is billed extra, so busy apps pay more than the headline price
  • Free tier keeps only 30 days of data and two users
  • Enterprise SSO and RBAC require the $300 Teams add-on on Pro or the Enterprise plan

Which one fits

Choose Fiddler AI if you need

  • Enterprises needing audit trails and governance over AI agents in regulated industries
  • Platform teams unifying monitoring of predictive ML and LLM systems
  • Security teams enforcing PII and jailbreak policy at inference time

Choose Langfuse if you need

  • Engineering teams running LLM apps or agents in production who need traces and cost tracking
  • Organisations that must self-host observability data for compliance
  • Teams that want prompts, datasets and evals tied to the same traces

Fiddler AI vs Langfuse: the questions people ask

Is Fiddler AI cheaper than Langfuse?

Langfuse starts at $29/mo. Fiddler AI has a free tier; what its paid plans cost is not confirmed by us yet.

Does Fiddler AI or Langfuse have a free tier?

Both: Fiddler AI has a free tier, and Langfuse has a free tier.

Which has a public API, Fiddler AI or Langfuse?

Both ship a public API, so either can be built on; the fact table above shows the platforms each one runs on.

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