Datadog LLM Observability vs Lunary
Both are observability & tracing tools. Here is how they actually differ on price, billing model and deployment.
Datadog LLM Observability
LLM tracing bolted onto the Datadog APM platform. Bills per LLM span rather than per trace, which is the single most misunderstood thing about it - agentic workloads can burn the 40,000-span free tier in a day.
Lunary
A lightweight Apache-2.0 observability platform aimed at RAG pipelines and chatbots. The fastest path from nothing to basic tracing, with a free tier metered daily rather than monthly - which catches people out.
| Datadog LLM Observability | Lunary | |
|---|---|---|
| Category | Observability & Tracing | Observability & Tracing |
| Our rating | 3/5 | 3/5 |
| Starting price | $160/mo | Around $20-30/mo |
| Billing meter | span | event |
| Free plan | Yes | Yes |
| Free self-hosting | No or paid tier only | Yes, free |
| Best for | Teams already standardised on Datadog for infrastructure and APM, running LLM features inside a larger system, who value one pane of glass over best-in-class eval tooling and can model their span volume accurately. | Small teams shipping RAG pipelines or chatbots who want basic tracing working this afternoon, and who will either stay small or self-host before volume becomes expensive. |
Our verdict on Datadog LLM Observability
Datadog LLM Observability is the obvious pick if Datadog is already your monitoring platform, and a poor one otherwise. The correlation story is real - being able to trace an LLM latency spike down through the service, host and database in one product is something no AI-native competitor matches. The eval tooling is competent but not the reason you would buy it. The thing that decides this product is billing. Datadog charges per LLM span, not per trace, and that distinction is where teams get hurt. A simple completion is 3 to 5 spans, but an agentic workflow with tool calls, retrieval and reasoning chains is commonly 20 to 50. Estimate your bill from requests and you will be wrong by more than an order of magnitude. Model span volume first, then decide.
Full Datadog LLM Observability review →Our verdict on Lunary
Lunary is a good starter tool that knows what it is. It is optimised for RAG pipelines and chatbots rather than trying to be a complete AI engineering platform, it is Apache 2.0 and self-hostable, and it is among the fastest things in the category to get running. Radar - which buckets responses against criteria you define - is a genuinely useful idea for spotting patterns that individual traces hide. Two caveats matter. The free tier is 1,000 events per day rather than per month, which is a meaningfully tighter constraint than the headline suggests and will not survive a real chatbot for long. And published pricing is inconsistent across sources in a way we could not resolve, with figures ranging from around $20 to $200 a month depending on where you look. Against Langfuse it is lighter on nearly every axis, and Langfuse is the better default for most teams. Lunary earns its place when speed to first trace matters more than depth.
Full Lunary review →Frequently Asked Questions
What is the main difference between Datadog LLM Observability and Lunary?
Datadog LLM Observability: Teams already standardised on Datadog for infrastructure and APM, running LLM features inside a larger system, who value one pane of glass over best-in-class eval tooling and can model their span volume accurately. Lunary: Small teams shipping RAG pipelines or chatbots who want basic tracing working this afternoon, and who will either stay small or self-host before volume becomes expensive. Both sit in Observability & Tracing, so the decision usually comes down to billing model and deployment rather than raw capability.
Which is cheaper, Datadog LLM Observability or Lunary?
It depends entirely on your workload shape, because they meter differently - Datadog LLM Observability bills on span and Lunary bills on event. Published starting prices are $160/mo and Around $20-30/mo respectively, but those numbers are not comparable until you apply them to the same traffic. Use our cost calculator to model both against your own request volume and span count.
Can I self-host Datadog LLM Observability or Lunary?
Datadog LLM Observability: No or paid tier only. Lunary: Yes, free. Free self-hosting means no licence fee, not no cost - you still own the infrastructure, upgrades and on-call.