Langfuse Cloud is the best AI observability platform: it publishes every tier, from a free Hobby plan with 50k units a month to Enterprise at $2,499 a month, and its core stays open source under the MIT license. LangSmith is #2 with 14-day and 180-day trace retention. Arize AX is #3 at a flat $50 a month. Opik is the cheapest paid cloud plan at $19 a month.
Hobby is free with 50k units a month; Core is $29, Pro is $199 and Enterprise is $2,499 a month, each with 100k units; Pro Teams add-on is $300 a month
Teams that want open-source tracing with a published price at every tier
Teams already on New Relic that want AI traces in the same platform
Pick by what you want
Best overall
Langfuse Cloud
Best for LangChain
LangSmith
Best flat-price managed tier
Arize AX
Best for Datadog shops
Datadog LLM Observability
Cheapest paid cloud plan
Opik
Best gateway logging
Helicone
The ranking
1
Langfuse Cloud
Answrs VerdictThe most fully published price and limit table here, backed by an open-source core.
Price: Hobby is free with 50k units a month; Core is $29, Pro is $199 and Enterprise is $2,499 a month, each with 100k units; Pro Teams add-on is $300 a monthExtra usage: Beyond the included units it is $8.00 per 100k units from 100k to 1M, falling to $6.00 per 100k at 50M and above; not available on HobbyData access: Hobby 30 days, Core 90 days, Pro and Enterprise 3 years; Hobby has 2 users and the paid plans have unlimited usersWhat it records: Structured logs of every request: the exact prompt, the response, token usage, latency, and any tool or retrieval stepsOwnership: ClickHouse acquired Langfuse; the post says it stays open source under its MIT license for core features and Langfuse Cloud continues as a standalone service
Langfuse Cloud lists Hobby as free with 50k units a month, Core at $29, Pro at $199 and Enterprise at $2,499 a month, each paid plan with 100k units. Extra usage is $8.00 per 100k units from 100k to 1M, falling to $6.00 per 100k at 50M and above, and is not available on Hobby. Data access is 30 days on Hobby, 90 days on Core and 3 years on Pro and Enterprise. ClickHouse acquired Langfuse; the post says the core stays open source under its MIT license and Langfuse Cloud continues as a standalone service.
Go ifTeams that want open-source tracing with a published price at every tier
Skip ifYou need extra usage on a free plan, since Hobby cannot buy more
Why #1 over #2: It publishes more tiers and limits than LangSmith, whose extended-trace fee is not listed.
2
LangSmith
Answrs VerdictPer-seat plans with 14-day and 180-day trace retention stated.
Price: Developer is $0 per seat a month with 1 seat; Plus is $39 per seat a month with unlimited seats; Enterprise is customBase traces: Up to 5k base traces a month on Developer and up to 10k on Plus, then pay as you goRetention: Base traces are kept 14 days and extended traces 180 days; the page does not tie retention to a planWithout LangChain: The quickstart wraps plain OpenAI, Anthropic and Gemini clients, and other providers use the @traceable decoratorNot published: The extended-trace upgrade fee and Enterprise allowances are not given on the pricing page
LangSmith Developer is $0 per seat a month with 1 seat, and Plus is $39 per seat a month with unlimited seats; Enterprise is custom. Developer includes up to 5k base traces a month and Plus up to 10k, then pay as you go. Base traces are kept 14 days and extended traces 180 days. Its quickstart wraps plain OpenAI, Anthropic and Gemini clients, so LangChain is not required. The extended-trace upgrade fee is not published.
Go ifTeams building agents on LangChain tooling that also want seat-based pricing
Skip ifYou want a flat price instead of per-seat billing
Why #2 over #3: It states retention for both trace types, while Arize AX ties retention to its plans only.
3
Arize AX
Answrs VerdictA flat monthly price with spans, ingestion and retention all listed.
Price: AX Free is $0 and AX Pro is $50 a month; AX Enterprise is customAX Free limits: 25k trace spans, 1 GB ingestion and 15 days retention a month, with unlimited usersAX Pro limits: 50k trace spans, 10 GB ingestion and 30 days retention a month, with unlimited usersDeployment: AX Free and Pro are SaaS; AX Enterprise is SaaS or self-hostedBuilt on: Arize AX is a managed enterprise platform built on the same open standards as Phoenix
Arize AX Free is $0 and AX Pro is $50 a month, with unlimited users on both. Free covers 25k trace spans, 1 GB ingestion and 15 days retention a month; Pro covers 50k spans, 10 GB and 30 days. AX Enterprise is custom and can be SaaS or self-hosted. Arize describes AX as a managed enterprise platform built on the same open standards as Phoenix.
Go ifTeams that want a managed platform with a flat $50 tier and unlimited users
Skip ifYou need more than 15 days of retention on the free tier
Why #3 over #4: It lists spans, ingestion and retention in one table, while Phoenix lists no price.
4
Arize Phoenix
Answrs VerdictOpenTelemetry-native tracing and evals, but no published price.
Price: Not published on the Arize pricing page, which lists no Phoenix price or limitsTracing: Records step-by-step runs including model calls, retrieval and tool use; traces arrive over OpenTelemetry (OTLP)Evaluation: Scores traces and spans with LLM-based evaluators, code-based checks or human labelsStandards: Built on top of OpenTelemetry and powered by OpenInference instrumentationNot stated: The docs page we read names no license and does not say whether it can be self-hosted
Arize Phoenix has no price or limits on the Arize pricing page. Its docs say it records step-by-step runs, including model calls, retrieval and tool use, over OpenTelemetry (OTLP), and scores traces with LLM-based evaluators, code-based checks or human labels. It is built on OpenTelemetry and OpenInference. The docs page we read names no license and does not say whether it can be self-hosted.
Go ifEngineers who want OpenTelemetry-based tracing and evaluation from the same maker as Arize AX
Skip ifYou need a published price or limits before you start
Why #4 over #5: It is built on open standards, while Datadog bills per LLM span on its own platform.
5
Datadog LLM Observability
Answrs VerdictBilled per LLM span only, with three price levels published.
Price: Free tier is $0 a month; Pro starts at $160 a month on an annual commitment, $200 month-to-month or $240 on-demandIncluded: Free has up to 40K LLM spans a month with 15-day trace retention; Pro includes 100K LLM spans a monthExtra spans: Pro extra LLM spans are $3.50 per 10K on annual billing, $4.20 month-to-month or $5 on-demand; tool, workflow and retrieval spans are not billedName: The pricing page labels it Agent Observability (LLM Observability) and the docs call it Agent ObservabilityFeatures: End-to-end tracing, cost and latency dashboards, sensitive data scanning and prompt-injection detection
Datadog LLM Observability is $0 on Free with up to 40K LLM spans a month and 15-day trace retention. Pro starts at $160 a month on an annual commitment, $200 month-to-month or $240 on-demand, with 100K LLM spans included. Extra spans are $3.50 per 10K on annual billing. Only LLM spans are billed, not tool, workflow or retrieval spans. The pricing page labels the product Agent Observability (LLM Observability), and it is unavailable on the US-FED site.
Go ifTeams already on Datadog that want LLM traces next to their APM data
Skip ifYou are on the US-FED site, where the pricing page says it is unavailable
Why #5 over #6: It puts LLM traces next to existing Datadog data, while Braintrust is a separate tool.
6
Braintrust
Answrs VerdictClear data and score allowances, with the highest listed entry price among flat plans.
Price: Starter is $0 a month and Pro is $249 a month; Enterprise is customStarter limits: 1 GB processed data and 10K scores a month, 14-day retention, unlimited usersPro limits: 5 GB processed data and 50K scores a month, then 30-day retention with $0.50 per GB a month beyondOverage: Starter extra data is $4 per GB; Pro extra data is $3 per GBTracing: Turns every production request into a searchable trace, with a filterable logs table
Braintrust Starter is $0 a month and Pro is $249 a month; Enterprise is custom. Starter includes 1 GB of processed data and 10K scores a month with 14-day retention and unlimited users. Pro includes 5 GB and 50K scores a month with 30-day retention, then $0.50 per GB a month beyond. Extra data is $4 per GB on Starter and $3 per GB on Pro. Its docs describe turning every production request into a searchable trace.
Go ifTeams that want logs and scoring in one place and do not mind a higher entry price
Skip ifYou want a paid plan under $100 a month
Why #6 over #7: It publishes score allowances, which Helicone does not list.
7
Helicone
Answrs VerdictGateway-first logging with published tiers, but an unexplained ownership notice.
Price: Hobby is free; Pro is $79 a month and Team is $799 a month; Enterprise is contact salesHobby limits: 10,000 requests a month, 1 GB storage, 7-day retention and 1 seatPro and Team: Pro keeps data 1 month with unlimited seats; Team keeps it 3 months with 5 organizationsGateway: The AI Gateway is an OpenAI-compatible API with access to 100+ models and automatic loggingOwnership: The pricing page says Helicone is no longer part of Mintlify and gives no further details
Helicone Hobby is free with 10,000 requests a month, 1 GB storage, 7-day retention and 1 seat. Pro is $79 a month and Team is $799 a month, and Enterprise is contact sales. Pro keeps data 1 month with unlimited seats; Team keeps it 3 months with 5 organizations. Its AI Gateway is an OpenAI-compatible API with access to 100+ models and automatic logging. The pricing page says Helicone is no longer part of Mintlify and gives no further details.
Go ifTeams that want request logging through an OpenAI-compatible gateway
Skip ifYou need clarity on the company after the ownership notice
Why #7 over #8: It logs through a gateway, while Weave focuses on agent traces and evaluations.
8
Weights & Biases Weave
Answrs VerdictPublished ingestion allowances, shown on the CoreWeave pricing page.
Price: Free is $0 a month; Pro starts at $60 a month billed monthly; Enterprise is customWeave ingestion: Free has 1 GB a month and Pro has 1.5 GB a month; extra is $0.10 per MB on Pro and $0.20 per MB on EnterpriseSeats and storage: Free has up to 5 model seats and 5 GB; Pro has up to 10 seats and 100 GBEligibility: Pro is for early-stage teams with fewer than 50 employeesTracing: End-to-end observability for agent behavior, with traces organized into sessions and turns
Weights & Biases Weave pricing is shown on a CoreWeave page: Free is $0 a month, Pro starts at $60 a month billed monthly, and Enterprise is custom. Weave ingestion is 1 GB a month on Free and 1.5 GB on Pro; extra is $0.10 per MB on Pro and $0.20 per MB on Enterprise. Free has up to 5 model seats and 5 GB of storage, and Pro has up to 10 seats and 100 GB. Pro is for early-stage teams with fewer than 50 employees.
Go ifTeams already using Weights & Biases for experiments that want traces and evals alongside
Skip ifYour company has 50 or more employees and wants the Pro plan
Why #8 over #9: It publishes ingestion allowances, while Opik counts spans.
9
Opik
Answrs VerdictThe lowest paid cloud price on the list, at $19 a month.
Price: Open Source self-hosted is $0; Free Cloud is $0; Pro Cloud is $19 a month; Enterprise is customFree Cloud: 25k spans a month, up to 10 team members and 60 days of span retentionPro Cloud: 100k spans a month with extra at $5 per 100k, up to 50 team members, and retention extendable to 400 days for $29 per 100k spansTracing: Full execution trees with inputs, outputs, timing and metadata, plus cost tracking and 30+ frameworksPage conflict: The pricing FAQ says all plans have unlimited team members, which conflicts with the plan table
Opik from Comet is $0 self-hosted or on Free Cloud, and Pro Cloud is $19 a month. Free Cloud has 25k spans a month, up to 10 team members and 60 days of retention. Pro has 100k spans with extra at $5 per 100k, up to 50 team members, and retention extendable to 400 days for $29 per 100k spans. The pricing FAQ says all plans have unlimited team members, which conflicts with the plan table.
Go ifTeams that want the lowest listed cloud price and a self-hosted option
Skip ifYou need the team-member limit settled in writing
Why #9 over #10: It has the lowest paid cloud price on the list and a self-hosted option, while New Relic lists no separate AI price.
10
New Relic AI Monitoring
Answrs VerdictShares the platform free tier and lists no separate AI price.
Free tier: 100 GB a month of data ingest and one free full platform userPaid users: Standard is $10 for the first user and $99 for each additional user, with a maximum of 5Data ingest: $0.40 per GB beyond the free 100 GB on the original data optionFeatures: Tracing of agent and tool calls, model comparison on cost, performance and quality, token cost alerts and MCP request monitoringAI pricing: The AI monitoring page says usage-based pricing and that you can start with 100 GB and 1 user free; it lists no separate AI price
New Relic AI Monitoring shares the platform pricing: 100 GB a month of data ingest and one free full platform user. Standard is $10 for the first user and $99 for each additional user, with a maximum of 5, and ingest beyond the free 100 GB is $0.40 per GB on the original data option. The AI monitoring page lists agent and tool call tracing, model comparison on cost, performance and quality, token cost alerts and MCP request monitoring, but no separate AI price.
Go ifTeams already on New Relic that want AI traces in the same platform
Skip ifYou want a price specific to AI monitoring
How we ranked these
We ranked AI observability platforms by how fully each maker publishes price, limits and retention for tracing LLM and AI applications, then by what its own pages say it records, using only pages we read. Where a price or limit is not published we say so, and ownership notes repeat only what the maker or acquirer states. Facts are taken from each maker's own published information; check the official site before you buy.
Questions people ask
What is the best AI observability platform?
Langfuse Cloud is our top pick: it publishes every tier, from a free Hobby plan to Enterprise at $2,499 a month, and its core stays open source under the MIT license after the ClickHouse acquisition. LangSmith and Arize AX follow.
Which AI observability platform has the cheapest paid plan?
Opik Pro Cloud is listed at $19 a month, then Langfuse Core at $29 a month and Arize AX Pro at $50 a month. LangSmith Plus is priced per seat at $39 a month.
Is there a free AI observability tool?
Yes. Langfuse Hobby has 50k units a month, Arize AX Free has 25k trace spans, Datadog LLM Observability has up to 40K LLM spans, Braintrust Starter is $0 and Opik is $0 self-hosted or on Free Cloud.
Which platforms do not publish a price?
Arize Phoenix has no price or limits on the Arize pricing page, and New Relic lists no separate price for AI monitoring. Enterprise tiers at most makers are custom.
Listed monthly price of the cheapest paid plan that is not per seat (Datadog on an annual commitment; Weights & Biases Weave starts at) at a glance
Opik19 USD
Langfuse Cloud29 USD
Arize AX50 USD
Weights & Biases Weave60 USD
Helicone79 USD
Datadog LLM Observability160 USD
Braintrust249 USD
Listed monthly price of the cheapest paid plan that is not per seat (Datadog on an annual commitment; Weights & Biases Weave starts at), as published by each maker. Picks without a published figure are left off.
