9 Best LLM Observability Tools of 2026

1. 1

   Langfuse

   Open-source LLM engineering platform for tracing, prompt management and evaluations, available as a cloud service or self-hosted.

   9.1overall

   Open-source LLM engineering platform for tracing, prompt management and evaluations, available as a cloud service or self-hosted.

   Best forTeams that want open-source tracing with unlimited users at a low monthly price

   Adoption data

   50,000+ companiesLangfuse says more than 50,000 companies use its platform, and its site lists use by 21 of the Fortune 50.

   Langfuse, Langfuse: Open Source Agent Evals and Observability (2026): “50,000+ companies using Langfuse”

   Langfuse has the strongest published adoption among dedicated LLM observability tools: its site says more than 50,000 companies use it, that it processes more than 90 billion observations a month and that 21 of the Fortune 50 are users. It covers tracing, prompt management, datasets and evaluations, and it accepts data from Python and JavaScript SDKs, OpenTelemetry and proxy gateways such as LiteLLM. Pricing is simple at the low end. The Hobby plan is free with 50k units a month, and Core costs $29 a month for 100k units, unlimited users and 90 days of data, with extra usage at $8 per 100k units. Pro at $199 adds 3 years of data access, SOC 2 and ISO 27001 reports and a HIPAA-ready region. The core is open source, so teams can self-host it for free. ClickHouse acquired Langfuse in January 2026, and Langfuse already ran on ClickHouse for its data layer.

   Strengths

   • +Largest published company count in this comparison at 50,000+
   • +Unlimited users from the $29 Core plan
   • +Pro plan keeps 3 years of data for $199 a month

   Limitations

   • −SSO enforcement and fine-grained RBAC need the $300 a month Teams add-on
   • −Hobby plan is limited to 2 users and 30 days of data
   • −Enterprise plan starts at $2,499 a month

   SummaryLangfuse is the best choice for most teams shipping LLM features because it reports 50,000+ companies using it and charges $29 a month for unlimited users. Teams that need SSO enforcement should budget for the $300 Teams add-on.

2. 2

   LangSmith

   LangChain's platform for observing, evaluating and deploying LLM agents, usable with or without LangChain frameworks.

   8.8overall

   LangChain's platform for observing, evaluating and deploying LLM agents, usable with or without LangChain frameworks.

   Best forTeams building agents with LangChain or LangGraph

   Adoption data

   35% of the Fortune 500LangChain said in its October 2025 Series B announcement that 35 percent of the Fortune 500 use its services and that its frameworks have 90 million combined monthly downloads.

   LangChain, LangChain raises $125M to build the platform for agent engineering (2025): “Today, langchain and langgraph have a combined 90M monthly downloads, and 35 percent of the Fortune 500 use our services.”

   LangSmith is LangChain's commercial platform, and the company behind it publishes the broadest enterprise footprint in this group: in its October 2025 funding announcement it said 35 percent of the Fortune 500 use its services and that commercial LangSmith trace volume had grown 12 times year over year. The product covers tracing, evaluation and deployment for agents and works whether or not you build on the LangChain libraries. The free Developer plan gives one seat and 5k base traces a month. Plus costs $39 per seat per month, includes 10k base traces and adds access to deployment features, and usage beyond that is pay-as-you-go. Base traces are kept 14 days, and teams that need longer history can upgrade traces to the 180-day extended tier for an extra fee. Enterprise adds custom SSO, ABAC and RBAC. The trade-off is cost at scale, because both seats and traces add to the bill.

   Strengths

   • +Broadest published enterprise use in this comparison
   • +Tight fit with LangChain and LangGraph agents
   • +Startup program offers up to $10,000 in credits

   Limitations

   • −Per-seat pricing gets expensive for large teams
   • −Base traces are kept only 14 days
   • −Usage beyond included traces is pay-as-you-go, so bills vary with volume

   SummaryLangSmith is the best choice for teams building on LangChain or LangGraph because it traces those agents natively and LangChain reports use at 35 percent of the Fortune 500. Large teams should model seat costs at $39 each before committing.

3. 3

   Arize AX

   Arize's managed platform for agent observability and evaluation, built alongside its open-source Phoenix project.

   8.5overall

   Arize's managed platform for agent observability and evaluation, built alongside its open-source Phoenix project.

   Best forTeams that want an open-source start with Phoenix and a managed upgrade path

   Adoption data

   3M+ monthly downloadsArize reports more than 3 million monthly downloads of Phoenix, its open-source observability and evaluation project.

   Arize AI, Arize Phoenix: Open-source LLM tracing and evaluation (2026): “3M+ Downloads Monthly”

   Arize sells two related products: Phoenix, an open-source tracing and evaluation tool, and Arize AX, the managed platform. Phoenix is where the published adoption sits, with Arize reporting more than 3 million monthly downloads and more than 22 million monthly downloads of its OpenTelemetry instrumentation. AX Free costs nothing and includes 25k spans, 1 GB of ingestion and 15 days of retention, with unlimited users and evals. AX Pro costs $50 a month and raises that to 50k spans, 10 GB and 30 days. Both plans include Signal, which surfaces issues in production traffic and proposes fixes, at 10 and 25 issues a month. Enterprise plans are custom. Arize raised a $70 million Series C in February 2025. The span allowance on Pro is modest, so agent-heavy teams should estimate span counts per run before choosing a tier.

   Strengths

   • +Low $50 entry price with unlimited users
   • +Free open-source Phoenix for local or self-hosted use
   • +Phoenix reports 3M+ monthly downloads

   Limitations

   • −Pro includes only 50k spans, which busy agents can use up quickly
   • −Free plan keeps data only 15 days
   • −Enterprise pricing is not published

   SummaryArize AX is the best choice for teams that want to start free on open-source Phoenix and move to a managed service at $50 a month. Watch the 50k span allowance on Pro if your agents emit many spans per run.

4. 4

   Opik

   Comet's open-source platform for agent tracing, test suites and evaluation, offered as free software or a hosted cloud.

   8.5overall

   Comet's open-source platform for agent tracing, test suites and evaluation, offered as free software or a hosted cloud.

   Best forBudget-conscious teams that want generous span limits and long retention

   Adoption data

   23.3k GitHub starsThe Opik open-source repository on GitHub had 23,300 stars when we checked in November 2026.

   GitHub (comet-ml/opik), comet-ml/opik repository (2026): “Stars 23.3k stars”

   Opik is Comet's LLM and agent observability product, and it has the lowest paid entry price on this list. The open-source edition is free and, according to Comet, runs the same codebase as the hosted versions. Free Cloud covers up to 10 team members and 25k spans a month with 60-day retention, which is longer than most free tiers here. Pro Cloud costs $19 a month for up to 50 team members and 100k spans, with extra spans at $5 per 100k and an option to extend retention to 400 days at $29 per 100k spans. Features include agent tracing and analysis, test suites with assertions, an agent playground and more than 40 LLM-as-a-judge metrics. The project's README says Opik is built to log over 40 million traces a day. Its adoption evidence is the GitHub repository, with 23.3k stars, rather than a published customer count, so adoption is scored below the vendors that disclose customers.

   Strengths

   • +Cheapest paid plan in this comparison at $19 a month
   • +Open-source version uses the same codebase as the hosted service
   • +60-day retention even on the free cloud plan

   Limitations

   • −Adoption figure is GitHub stars, not a customer count
   • −Pro Cloud caps teams at 50 members
   • −Longer retention costs extra per 100k spans

   SummaryOpik is the best choice for small teams on a budget because Pro Cloud costs $19 a month for 100k spans and 60 days of retention. Teams that need a vendor with published enterprise customer counts may prefer Langfuse or LangSmith.

5. 5

   Datadog LLM Observability

   Datadog's agent and LLM monitoring product, which links LLM spans to APM, infrastructure and user sessions in the Datadog platform.

   8.4overall

   Datadog's agent and LLM monitoring product, which links LLM spans to APM, infrastructure and user sessions in the Datadog platform.

   Best forCompanies already running Datadog APM

   Adoption data

   6,500+ AI integration customersDatadog said on its first-quarter 2026 earnings call that more than 6,500 customers send data through one or more of its AI integrations; this covers all AI integrations, not only LLM Observability.

   Datadog (earnings call transcript published by The Motley Fool), Datadog (DDOG) Q1 2026 Earnings Call Transcript (2026): “We now have over 6,500 customers sending data for 1 or more of AI integrations.”

   Datadog LLM Observability, now presented as Agent Observability, is the natural pick for teams whose services already report to Datadog. It shares one tracer with Datadog APM, so an LLM call can be followed into the service, host and user session around it. The billing model is friendlier than it first looks: Datadog bills only LLM spans, and tool, workflow, agent, embedding and retrieval spans are free. The Free plan covers up to 40k LLM spans and Pro costs $160 a month for up to 100K, both with 15-day retention and unlimited context and evals. Datadog does not publish a customer count for this product, but on its first-quarter 2026 call it said more than 6,500 customers send data through its AI integrations and that span volume in LLM Observability nearly tripled quarter over quarter. That figure covers several AI products, so adoption is scored a step below the leaders.

   Strengths

   • +One tracer and workflow shared with the rest of Datadog
   • +Only LLM calls are billed, not every span in an agent run
   • +Backed by a public company with SEC-filed results

   Limitations

   • −$160 a month entry price is the second highest here
   • −15-day default retention
   • −Most value depends on already paying for Datadog

   SummaryDatadog LLM Observability is the best choice for teams already on Datadog because it ties LLM spans to APM and infrastructure data with one tracer. Teams without Datadog will find cheaper dedicated tools above.

6. 6

   Braintrust

   Evaluation and observability platform for production AI, with tracing, scorers, datasets and playgrounds.

   7.7overall

   Evaluation and observability platform for production AI, with tracing, scorers, datasets and playgrounds.

   Best forAI-native product teams that run evals on every change

   Braintrust is built around evaluation: experiments, scorers, datasets and playgrounds sit at the center, with tracing to feed production data back into tests. Its customers page features teams at Cloudflare and Box, and it raised an $80 million Series B led by ICONIQ in February 2026, but it does not publish a customer or user count, so its adoption score is conservative. The Starter plan is free with 1 GB of processed data, 10k scores, 14-day retention and $10 of model credits. Pro costs $249 a month and includes 5 GB of processed data at $3 per extra GB, 50k scores at $1.50 per extra thousand, 30-day retention, $100 of model credits, RBAC and custom charts. Every plan includes unlimited users, projects and experiments. Pro is the most expensive entry tier on this list, though qualifying startups can get it free for 6 to 12 months.

   Strengths

   • +Deepest focus on evals, scorers and experiments in this group
   • +Unlimited users on every plan
   • +Qualifying startups can get Pro free for 6 to 12 months

   Limitations

   • −Highest paid entry price here at $249 a month
   • −No published customer or user count
   • −Starter keeps data only 14 days

   SummaryBraintrust is the best choice for AI-native teams that gate releases on evals because scores, datasets and experiments are its core and every plan has unlimited users. The $249 Pro entry price is high for small teams.

7. 7

   Pydantic Logfire

   Observability platform from the Pydantic team that stores AI traces, evals, logs and metrics in one SQL-queryable table.

   7.6overall

   Observability platform from the Pydantic team that stores AI traces, evals, logs and metrics in one SQL-queryable table.

   Best forPython teams that want AI and application telemetry in one place

   Logfire comes from the team behind the Pydantic library and takes a general observability approach: AI traces, logs, metrics, eval results and prompt versions all land in one table that you query with Postgres-compatible SQL. It has native SDKs for Python, TypeScript and Rust and accepts standard OpenTelemetry from anything else, and Pydantic lists support for more than 26 agent frameworks. Pricing uses one record-based meter. Every plan includes 10M records a month, and the Personal plan is free and hard-capped at $0 with 3 projects and 30-day retention. Team costs $49 a month, adds unlimited agent, service and host monitoring, AI output evaluations with human review and 5 seats, and charges $2 per million extra records up to a cap you set. Pydantic does not publish a Logfire customer count, so adoption is scored conservatively.

   Strengths

   • +One meter covers AI, application and infrastructure telemetry
   • +Hard spending caps prevent surprise bills
   • +AI output evaluations and human review on Team

   Limitations

   • −No published customer or user count
   • −Team plan includes only 5 seats
   • −Fewer prompt management features than dedicated LLM tools

   SummaryPydantic Logfire is the best choice for Python teams that want LLM traces and application telemetry in one SQL table because it meters both on a single record count. Teams that need deep prompt management should look higher on the list.

8. 8

   Helicone

   Open-source LLM request logging and gateway with caching, rate limits and fallbacks.

   7.3overall

   Open-source LLM request logging and gateway with caching, rate limits and fallbacks.

   Best forTeams that want request-level logging through a gateway

   Adoption data

   6.3k GitHub starsHelicone's open-source repository on GitHub had 6,300 stars when we checked in November 2026.

   GitHub (Helicone/helicone), Helicone/helicone repository (2026): “Stars 6.3k stars”

   Helicone logs LLM traffic at the request level and doubles as a gateway, with caching, rate limits and automatic fallbacks between providers. The Hobby plan is free with 10,000 requests, 1 GB of storage and one seat. Pro costs $79 a month plus usage-based charges, with a 7-day free trial, and adds unlimited seats, alerts, reports and HQL, Helicone's query language. Team costs $799 a month and adds 5 organizations, SOC 2 and HIPAA compliance and a dedicated Slack channel. Data retention runs from 7 days on Hobby to 1 month on Pro and 3 months on Team. Helicone's adoption evidence is its open-source GitHub repository, with 6.3k stars, and its homepage currently carries a banner saying it is no longer part of Mintlify with details to come. That ownership change is worth watching before a long commitment, and it is one reason Helicone ranks last here.

   Strengths

   • +Gateway features such as caching and fallbacks sit beside logging
   • +Unlimited seats on Pro
   • +Startups under 2 years old can get 50 percent off the first year

   Limitations

   • −Usage-based charges apply on top of the $79 Pro fee
   • −Site banner says Helicone is no longer part of Mintlify, with details pending
   • −Thinner evaluation tooling than Braintrust or Langfuse

   SummaryHelicone is the best choice for teams that want LLM logging and a gateway with caching and fallbacks in one service, from $79 a month. Confirm the company's ownership and roadmap before signing a long contract.

9. 9

   W&B Weave

   Weights & Biases' toolkit for tracing, evaluating and monitoring AI applications, now sold within CoreWeave's platform.

   7.3overall

   Weights & Biases' toolkit for tracing, evaluating and monitoring AI applications, now sold within CoreWeave's platform.

   Best forTeams already tracking model training in Weights & Biases

   Weave is the LLM side of Weights & Biases, which CoreWeave acquired in May 2025, and its pricing now sits on a CoreWeave Forge pricing page alongside inference and sandbox products. The free plan includes AI application tracing, evaluations and scorers, plus experiment tracking and a model registry, with 1 GB a month of Weave data ingestion. Pro starts at $60 a month billed monthly with a 30-day free trial, includes 1.5 GB of ingestion and charges $0.10 per extra MB, and adds unlimited teams, team-based access controls and service accounts. Ingestion counts trace metadata and full LLM inputs and outputs, so teams logging long prompts should estimate data volume carefully. The main reason to pick Weave is that traces and evaluations live next to model training runs. Neither W&B nor CoreWeave publishes a Weave customer count, so adoption is scored conservatively.

   Strengths

   • +Traces and evals sit next to training runs in the same account
   • +30-day free trial of Pro
   • +Backed by CoreWeave, a public company

   Limitations

   • −Ingestion overage at $0.10 per MB adds up fast for verbose traces
   • −No published customer count for Weave
   • −Pricing page now mixes Weave with CoreWeave inference and sandbox products

   SummaryW&B Weave is the best choice for teams already using Weights & Biases because LLM traces and evals sit beside their training experiments. Teams starting fresh will find lower overage rates elsewhere.

Questions or corrections: editorial@statlyst.com · Disclosure