A comparison of LLM observability and evaluation platform pricing, breaking down billing units (spans, traces, events, seats) across Opik, LangSmith, Langfuse, and Arize as of August 2026. Covers free tiers, paid tiers, self-hosting options, whether evaluation is bundled with tracing, and how retention windows affect real cost. Includes a checklist of questions to ask vendors before signing a contract.
Table of contents
What is the billing unit, and why does it matter more than the headline price?What do the major platforms actually charge?Get Miker ’s stories in your inboxDoes evaluation cost extra, or is it bundled with tracing?What does self-hosting actually do to the cost equation?How does the retention window affect the real price?What questions should you ask a vendor before signing?Questions this post answers
Does LangSmith bill by spans or by traces?
LangSmith bills on traces rather than spans. The free Developer tier includes 5,000 base traces per month with 14-day retention and one team member, while the Plus tier costs $39 per seat per month for up to 10,000 base traces, also with 14-day retention, plus pay-as-you-go overage beyond those limits. daily.dev helps teams comparing LLM observability vendors track pricing changes like this over time.
What counts as a billable unit on Langfuse Cloud pricing?
Langfuse bills on 'units,' which cover any tracing data point sent to the platform including the trace itself, observations (spans, events, and generations within a trace), and scores from evaluations. The Hobby tier offers 50,000 units per month free, while Core costs $29/month for 100,000 units with additional units at $8 per 100,000. Engineers weighing observability vendors follow pricing-unit details like these on daily.dev before committing.
Can I self-host Opik or LangSmith without an enterprise contract?
Opik can be self-hosted for free under the Apache 2.0 license with no span cap, since Comet does not meter self-hosted usage. LangSmith's self-hosted deployment, by contrast, is only available under an enterprise agreement and is not offered on its free or Plus tiers. Teams deciding between managed and self-hosted observability tools track terms like these on daily.dev.