Perimattic

LLM Observability Cost Calculator

Compare what Langfuse, LangSmith and Datadog would cost for your trace volume, spans per trace, team size and retention. Prices come from each vendor's own pricing page, checked 1 October 2026, and every rate is editable.

Compare costsHow vendors charge
  • Free, no sign-up
  • 3 vendors compared
  • Prices checked 1 October 2026
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Describe your workload

Enter monthly volumes. Results update as you type.

Volume

One trace = one request or agent run.

Model calls, tool calls and retrieval steps inside one trace.

For example one faithfulness score per answer.

Team & retention

Enter your workload and press Compare costs to see estimated monthly cost for each vendor, the plan that fits, and what each one meters.
Pricing assumptions and sources (checked 1 October 2026)

Defaults are published list prices. Rates marked “reported” are not shown on the vendor's main pricing page and come from a secondary source; check them before relying on the total. Edit any value to use your own quote.

Sources: Langfuse pricing, Langfuse billable units, LangSmith pricing, Datadog Agent Observability.

What You Get

How LLM observability tools charge

The three vendors meter different things, which is why the same workload can cost very different amounts.

Langfuse: units

Every trace, observation (span or generation) and evaluation score counts as one unit. Long agent traces use more units than simple chatbot calls.

LangSmith: traces and seats

One trace is one run of your application, however many steps it has. Paid plans add a fee per seat, so team size matters as much as volume.

Datadog: LLM spans

Agent Observability bills LLM spans per month, with a free tier and a Pro plan. Longer retention is an add-on.

Retention changes the plan

Keeping traces longer moves you to a different plan or rate on every vendor. Regulated teams often need months or years, not days.

Self-hosting

The open-source Langfuse core can be self-hosted for free, and LangSmith offers self-hosting on Enterprise. Infrastructure and staff time are not included here.

Editable assumptions

Every rate is editable, with the source and check date shown, so you can plug in a quote or a negotiated price.
Choosing a tool

Price is only part of the decision

The cheapest tool for your volume may not fit your stack or your obligations. LangSmith fits teams built on LangChain, Langfuse fits teams that want open source or self-hosting, and Datadog fits teams already running Datadog for infrastructure. All three accept OpenTelemetry, so you can trial more than one without rewriting instrumentation.

Regulated teams should also ask how traces become audit evidence. That is the gap Perimattic AI Suite is built for, and LangSmith vs Langfuse compares the two most common open choices.

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FAQ

Frequently asked questions

How much does Langfuse cost?

Langfuse Cloud has a free Hobby plan with 50,000 units a month, and paid plans at $29 (Core), $199 (Pro) and $2,499 (Enterprise) per month, each with 100,000 units included. Extra usage starts at $8 per 100,000 units and gets cheaper with volume. A unit is a trace, an observation (span or generation) or a score. Self-hosting the MIT-licensed open-source core is free apart from your infrastructure.

How much does LangSmith cost?

LangSmith’s Developer plan is free for one seat with 5,000 base traces a month. Plus costs $39 per seat per month with 10,000 base traces included, and usage above that is billed per 1,000 traces. Base traces are kept for 14 days and extended traces for 180 days at a higher rate. Enterprise pricing, including self-hosting, is custom.

How much does Datadog LLM Observability cost?

Datadog now sells the product as Agent Observability. Its pricing page lists a free tier for up to 40,000 LLM spans a month with 15-day retention and a Pro tier at $160 a month that includes 100,000 LLM spans, with more usage billed per 10,000 spans. Longer retention is an add-on. Annual and monthly commitments are priced differently.

Why do the three tools give such different totals for the same workload?

They meter different things. Langfuse counts every trace, observation and score, so traces with many spans cost more. LangSmith counts traces and charges per seat. Datadog counts LLM spans. A workload with long agent traces and a small team often favours LangSmith; a large team with simple traces often favours Langfuse. That is why it is worth modelling your own numbers.

Does this include the cost of self-hosting?

No. The open-source Langfuse core has no licence fee, but you pay for servers, databases, storage and the engineering time to run them. Use the self-host vs SaaS cost calculator to estimate that side.

How much does Perimattic AI Suite cost?

Perimattic AI Suite is in early access and does not publish a price list yet. Pricing is agreed with each early-access team based on the use case and deployment, so it is not included in the comparison.

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Need Expert Help?

Choosing an observability stack for regulated AI?

Perimattic AI Suite traces, evaluates and costs every model call and agent step, and turns that telemetry into evidence mapped to HIPAA, SOC 2, the EU AI Act and DORA.

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