Compare · 15 platforms

Agent observability and evaluation platforms compared

Langfuse, LangSmith, Arize, Braintrust, Helicone and ten more, side by side on tracing, evals, runtime controls, licence and pricing. Every value was checked against the vendor's own pages on 20 October 2026.

Prefactor is an agent evaluation platform for teams building AI agents: it observes every agent run from development to production, evaluates whether the agent did its job, and shows how to improve it.

Compare capabilities →Compare any two
§01 / THE SHORT ANSWERtl;dr: which, and when
TL;DR

Which agent observability and evaluation platform should you use?

It depends on three things: where your traces are allowed to live, which stack you already run, and whether you need to act on a bad run or only find it afterwards. To score every agent run in production and act on a failing one (hold it for approval, block the action or stop the run), Prefactor; Galileo and Maxim AI also offer guardrails during a run. For free self-hosting, Langfuse (MIT) and Opik (Apache-2.0) are the open-source options. On LangChain, LangSmith. If you already run Datadog, Splunk or Dynatrace, each now sells its own agent product (Splunk through Galileo, Dynatrace through Arize). For an experiment-led eval loop, Braintrust.

Which platform to look at, by need (20 October 2026)
If you needLook at
Scoring production agent runs and acting on failuresPrefactor: every run is scored, and runtime policies, approval holds and a kill switch act on what the scores find.
Blocking or holding an agent action during the runPrefactor, Galileo (Agent Control) and Maxim AI (Bifrost guardrails, Enterprise). Several others offer partial, model-call-only controls.
Open source, free to self-hostLangfuse (MIT) or Opik (Apache-2.0). Arize Phoenix is source-available under the Elastic License. Prefactor publishes its deterministic evals package under Apache-2.0.
Building on LangChain or LangGraphLangSmith, built by the LangChain team. Prefactor also has a native LangChain SDK.
An experiment-led eval loopBraintrust, organised around datasets, experiments and an analysis agent.
Already on Datadog, Splunk or DynatraceDatadog Agent Observability; Galileo (now Splunk Agent Observability); Arize (now part of Dynatrace).
Pydantic AI and full-stack OpenTelemetryPydantic Logfire. Prefactor also accepts OpenTelemetry.
An open-source eval library firstConfident AI, makers of DeepEval.
Catching issues in real user conversationsRaindrop, which classifies production events into signals and issues.
Simulating agents, including voice, before releaseMaxim AI. Prefactor has a native LiveKit SDK for evaluating voice agents in production.
Classic ML models and LLM apps in one placeFiddler.
§02 / WHAT CHANGEDas of: 20 October 2026

Which agent observability vendors changed owners?

As of 20 October 2026, five of the 15 have changed hands since 2025. Ownership affects roadmaps, pricing and how long a product stays as it is.

Ownership and status changes
VendorWhenWhat changed
W&B WeaveMay 2025Weights & Biases acquired by CoreWeave; W&B hosted accounts moved to CoreWeave Forge in September 2026
LangfuseJanuary 2026Acquired by ClickHouse; licence and self-hosting unchanged, per Langfuse
HeliconeMarch 2026Acquired by Mintlify and moved to maintenance mode; new cloud sign-ups disabled. On 19 October 2026 Helicone said it is no longer part of Mintlify, with no new owner named
GalileoMay 2026Acquired by Cisco; sold as Splunk Agent Observability since 7 August 2026
ArizeOctober 2026Acquisition by Dynatrace completed on 1 October 2026; Phoenix and AX continue
§03 / CAPABILITIESby question: who does what

Which platform has which capability?

Each answer covers all 16 platforms on this page: the 15 compared vendors and Prefactor, which publishes it. Answers are generated from the vendor research. Green means the vendor documents it, amber means it is limited (for example to model calls, one plan or a preview), and grey means no or not stated.

Which platforms can block or hold a live agent action?

As of 20 October 2026, 3 of the 16 platforms on this page can block or hold a live agent action: Prefactor, Galileo and Maxim AI. 8 do so in part: LangSmith, Arize, Helicone, Datadog, Fiddler, Logfire, Opik and W&B Weave. 5 do not: Langfuse, Braintrust, HoneyHive, Confident AI and Raindrop.

Which platforms evaluate production traffic automatically?

As of 20 October 2026, 15 of the 16 platforms on this page score live production traffic automatically: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Logfire, Opik, Raindrop, Maxim AI and W&B Weave. 1 does so in part: Helicone.

Which platforms trace multi-step agent runs and tool calls?

As of 20 October 2026, 15 of the 16 platforms on this page trace multi-step agent runs, including tool calls and nested spans: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Logfire, Opik, Raindrop, Maxim AI and W&B Weave. 1 does so in part: Helicone.

Which platforms run offline evals on datasets?

As of 20 October 2026, 14 of the 16 platforms on this page run offline evals on datasets and experiments: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Logfire, Opik, Maxim AI and W&B Weave. 2 do so in part: Helicone and Raindrop.

Which platforms support LLM-as-a-judge scoring?

As of 20 October 2026, 14 of the 16 platforms on this page support LLM-as-a-judge scoring: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Logfire, Opik, Maxim AI and W&B Weave. 2 do so in part: Helicone and Raindrop.

Which platforms support code-based evaluators?

As of 20 October 2026, 14 of the 16 platforms on this page support code-based evaluators: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Logfire, Opik, Maxim AI and W&B Weave. 1 does so in part: Raindrop. One does not: Helicone.

Which platforms support human review and annotation?

As of 20 October 2026, 12 of the 16 platforms on this page support human review and annotation: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Opik, Maxim AI and W&B Weave. 4 do so in part: Helicone, Fiddler, Logfire and Raindrop.

Which platforms include prompt versioning and a playground?

As of 20 October 2026, 12 of the 15 platforms on this page include prompt versioning and a playground: Langfuse, LangSmith, Arize, Braintrust, Helicone, HoneyHive, Confident AI, Datadog, Logfire, Opik, Maxim AI and W&B Weave. 1 does so in part: Galileo. 2 do not: Fiddler and Raindrop. Prefactor evaluates how prompts perform in live runs rather than providing a prompt playground or registry.

Which platforms track the cost of LLM and agent calls?

As of 20 October 2026, 15 of the 16 platforms on this page track cost per call or run: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Helicone, Galileo, HoneyHive, Confident AI, Datadog, Logfire, Opik, Raindrop, Maxim AI and W&B Weave. 1 does so in part: Fiddler.

Which platforms support OpenTelemetry?

As of 20 October 2026, 15 of the 16 platforms on this page accept or export OpenTelemetry traces: Prefactor, Langfuse, LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Logfire, Opik, Raindrop, Maxim AI and W&B Weave. 1 does so in part: Helicone.

Which platforms include a gateway or proxy?

As of 20 October 2026, 4 of the 15 platforms on this page include a gateway or proxy in the request path: Braintrust, Helicone, Logfire and Maxim AI. 2 do so in part: Arize and Opik. 9 do not: Langfuse, LangSmith, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Raindrop and W&B Weave. Prefactor instruments agents through SDKs and OpenTelemetry, so it adds no gateway to the request path.

Which agent observability platforms are open source?

As of 20 October 2026, 3 of the 15 platforms on this page publish their platform as open source: Langfuse, Helicone and Opik. 12 do so in part: LangSmith, Arize, Braintrust, Galileo, HoneyHive, Confident AI, Datadog, Fiddler, Logfire, Raindrop, Maxim AI and W&B Weave. Prefactor publishes its deterministic agent evals package under Apache-2.0; the platform itself is hosted.

Which platforms can be self-hosted?

As of 20 October 2026, 10 of the 15 platforms on this page can be self-hosted: Langfuse, LangSmith, Arize, Helicone, Galileo, HoneyHive, Fiddler, Opik, Maxim AI and W&B Weave. 4 do so in part: Braintrust, Confident AI, Logfire and Raindrop. One does not: Datadog. Prefactor is hosted, with enterprise deployments in the customer's region or environment.

Which platforms trace LLM calls?

As of 20 October 2026, all 16 platforms on this page trace LLM calls.

§04 / PRICINGas of: 20 October 2026

How much do agent observability platforms cost?

As of 20 October 2026, in US dollars, as listed on each vendor's pricing page. Vendors meter on different units (spans, traces, events, gigabytes, seats), so compare on your own volumes.

Pricing by platform, 20 October 2026
PlatformPricing
LangfuseHobby is free with 50k units a month and 30 days of data, and self-hosting is free. Core is $29 a month for 100k units, then $8 per 100k. Pro is $199 a month, and Enterprise is $2,499 a month or custom.
LangSmithDeveloper is free for one seat and 5k base traces a month. Plus is $39 per seat a month with 10k base traces; the overage rate is not published. Enterprise is a custom annual contract.
ArizeAX Free is $0 for 25k spans a month with 15-day retention. AX Pro is $50 a month for 50k spans with 30-day retention. AX Enterprise is custom and is the only self-hosted AX option. Phoenix is free to self-host.
BraintrustStarter is free with 1 GB of processed data, 10K scores and 14-day retention. Pro is $249 a month with 5 GB and 50K scores. Every plan includes unlimited users. Enterprise, the only plan with self-hosting, is custom.
HeliconeHobby is free with 10K requests, Pro is $79 a month and Team $799 a month, with Enterprise custom. New cloud sign-ups have been disabled since March 2026, so new customers cannot start on any plan.
GalileoSplunk lists Agent Observability from $100 a month per 1.2 million spans a year, billed annually, with a Luna model allowance. No free tier is listed. On-premises deployment is available.
HoneyHiveThe Developer tier is free with 10,000 events a month, 30-day retention and up to 5 users. There is no published self-serve paid plan; Enterprise, including self-hosting, is quote-based.
Confident AIFree covers 2 seats and 1 GB-month of trace data. Starter is $200 a month per organisation with unlimited seats, and Team is $2,000 a month. Enterprise is custom.
DatadogFree covers 40K LLM spans a month with 15-day retention. Pro is $160 a month billed annually for 100K LLM spans, then $3.50 per 10K. Only LLM spans are billed; tool and agent spans are not.
FiddlerA free plan covers guardrails only, through a demo request. The Developer plan is $0.002 per trace. Enterprise, which adds VPC and on-premises deployment, is quote-based.
LogfirePersonal is free with 10M records a month. Team is $49 a month and Growth $249 a month, each with 10M records included, then $2 per extra million. Enterprise is custom.
OpikSelf-hosting is free with unlimited spans. Free Cloud covers 25k spans a month and 10 users. Pro Cloud is $19 a month for 100k spans, then $5 per 100k. Enterprise is custom.
RaindropHobby is free with 1,000 events a month. Pro is $299 a month plus $0.003 per event up to 1M events. Enterprise is custom.
Maxim AIDeveloper is free for up to 3 seats and 10k logs a month. Professional is $29 per seat a month and Business $49 per seat a month. Enterprise, the only plan with in-VPC hosting, is custom.
W&B WeaveForge Free includes 1 GB of Weave ingestion a month. Forge Pro starts at $60 a month with 1.5 GB, for teams under 50 people; the pricing page lists extra ingestion at $0.10 per MB. Enterprise is custom.
PrefactorDev is free with 5,000 spans a month. Startup is $49 a month and Scaleup $199 a month. Enterprise is custom above 4 million spans a month.
§05 / THE PLATFORMSprofiles: what each is, who it suits

What is each platform?

Publishes this page

What is Prefactor?

Prefactor is an agent evaluation platform for teams building AI agents: it observes every agent run from development to production, evaluates whether the agent did its job, and shows how to improve it.

Best for: Teams running agents in production who need every run scored against what the agent was meant to do, and the ability to hold or stop an action when evaluation flags it.

Open source: Partly. Its deterministic evals package is Apache-2.0; the platform is hosted.

Acts during a run: Yes. Runtime policies can block, throttle, sandbox or escalate an agent's tool calls and data access before they run, approval routing holds risky actions for a person, and a kill switch stops a run, an agent or a team.

PlatformPricingOpen-source evals

What is Langfuse?

Langfuse is an open-source LLM engineering platform for tracing, evaluating and versioning prompts in LLM and agent applications, available as a hosted cloud service or self-hosted for free.

Status: Acquired by ClickHouse; licence and self-hosting unchanged, per Langfuse

Best for: Teams that want an open-source, self-hostable platform combining tracing, prompt versioning and offline and online evaluation for LLM and agent applications.

Open source: Yes. The repository is MIT-licensed, apart from add-on features in its ee folders that need a licence key. Self-hosting on Docker or Kubernetes is free.

Acts during a run: No. Langfuse evaluates runs after they happen. Its documentation says run-time protection comes from separate libraries, and Langfuse scores those measures afterwards.

Langfuse websiteLangfuse vs ArizeLangfuse vs BraintrustLangfuse vs Confident AILangfuse vs DatadogLangfuse vs FiddlerLangfuse vs GalileoLangfuse vs HeliconeLangfuse vs HoneyHiveLangfuse vs LangSmithLangfuse vs LogfireLangfuse vs Maxim AILangfuse vs OpikLangfuse vs RaindropLangfuse vs W&B Weave

What is LangSmith?

LangSmith is LangChain's commercial platform for tracing, monitoring and evaluating LLM agents, with prompt versioning, agent deployment, an LLM gateway in beta and Engine, an agent that drafts fixes from production traces.

Best for: Teams building on LangChain or LangGraph, or wanting tracing, evaluation, prompt versioning and agent deployment from one vendor, with self-hosting available on an Enterprise contract.

Open source: Partly. The client SDKs are MIT-licensed and the LangChain frameworks are open source, but the LangSmith platform is proprietary. Self-hosting requires an Enterprise contract.

Acts during a run: Partly. The LLM Gateway, in public beta since July 2026, can cap spend, restrict models and redact personal data in model calls. It does not cover tool calls; LangChain describes tool and MCP gateways as planned.

LangSmith websiteLangSmith vs ArizeLangSmith vs BraintrustLangSmith vs Confident AILangSmith vs DatadogLangSmith vs FiddlerLangSmith vs GalileoLangSmith vs HeliconeLangSmith vs HoneyHiveLangSmith vs LangfuseLangSmith vs LogfireLangSmith vs Maxim AILangSmith vs OpikLangSmith vs RaindropLangSmith vs W&B Weave

What is Arize?

Arize is an AI observability and evaluation vendor with two products: Phoenix, a source-available tool you self-host for free, and Arize AX, a commercial platform for continuous production evals, monitoring and alerting.

Status: Acquisition by Dynatrace completed on 1 October 2026; Phoenix and AX continue

Best for: Teams wanting OpenTelemetry-based tracing and evaluation with a free self-hosted option (Phoenix) and a path to a hosted platform with continuous online evals, monitors and alerting (AX), including organisations already using Dynatrace.

Open source: Partly. Phoenix's code is public under the Elastic License 2.0, which is source-available rather than open source: you can self-host and modify it but not offer it to others as a hosted service. AX is commercial.

Acts during a run: Partly. Arize AX documents guards built on the Guardrails AI framework that run in your own code around model calls. There is no documented approval or policy layer for agent tool actions.

Arize websiteArize vs BraintrustArize vs Confident AIArize vs DatadogArize vs FiddlerArize vs GalileoArize vs HeliconeArize vs HoneyHiveArize vs LangfuseArize vs LangSmithArize vs LogfireArize vs Maxim AIArize vs OpikArize vs RaindropArize vs W&B Weave

What is Braintrust?

Braintrust is a hosted AI evaluation and observability platform covering tracing, offline experiments, online scoring, human review and prompt versioning, with an LLM gateway in preview and Loop, an in-product analysis agent.

Best for: Teams that want one hosted product for offline experiments, online scoring, human review and prompt iteration, with broad SDK and agent framework coverage.

Open source: Partly. The platform is proprietary. Its SDKs, the Autoevals scoring library and its Terraform deployment modules are open source.

Acts during a run: No. Online scoring, alerts and Patterns judge traces after they are logged. Braintrust does not document blocking, guardrails or approvals on live agent actions.

Braintrust websiteBraintrust vs ArizeBraintrust vs Confident AIBraintrust vs DatadogBraintrust vs FiddlerBraintrust vs GalileoBraintrust vs HeliconeBraintrust vs HoneyHiveBraintrust vs LangfuseBraintrust vs LangSmithBraintrust vs LogfireBraintrust vs Maxim AIBraintrust vs OpikBraintrust vs RaindropBraintrust vs W&B Weave

What is Helicone?

Helicone is an open-source (Apache-2.0) LLM observability platform and AI gateway that logs model requests through a proxy or SDKs. It has been in maintenance mode since March 2026 and is not taking new cloud sign-ups.

Status: Acquired by Mintlify and moved to maintenance mode; new cloud sign-ups disabled. On 19 October 2026 Helicone said it is no longer part of Mintlify, with no new owner named

Best for: Existing Helicone users or teams wanting a self-hostable, Apache-2.0 LLM request logger and gateway with cost tracking, who accept that the product has been in maintenance mode since March 2026 and that its ownership is in flux.

Open source: Yes. The main repository is Apache-2.0 and can be self-hosted. Its separate Rust AI gateway is GPL-3.0 and has not been updated since November 2025.

Acts during a run: Partly. Its gateway can block prompt injection and jailbreak attempts, for OpenAI models only, and apply rate limits. There are no approvals or policies on agent tool actions.

Helicone websiteHelicone vs ArizeHelicone vs BraintrustHelicone vs Confident AIHelicone vs DatadogHelicone vs FiddlerHelicone vs GalileoHelicone vs HoneyHiveHelicone vs LangfuseHelicone vs LangSmithHelicone vs LogfireHelicone vs Maxim AIHelicone vs OpikHelicone vs RaindropHelicone vs W&B Weave

What is Galileo?

Galileo is an evaluation, observability and guardrail platform for LLM and agent applications. Cisco acquired it in May 2026, and since August 2026 it has been sold as Splunk Agent Observability.

Status: Acquired by Cisco; sold as Splunk Agent Observability since 7 August 2026

Best for: Teams already using, or moving to, Splunk Observability Cloud who want agent evaluation, production monitoring and runtime guardrails alongside infrastructure telemetry, including on-premises or air-gapped deployments.

Open source: Partly. The platform is proprietary. Its Python and TypeScript SDKs and Agent Control, its run-time guardrail layer, are open source under Apache-2.0.

Acts during a run: Yes. Agent Control checks model and tool inputs and outputs during a run and can block prompt injection, personal data leaks and harmful content using rules set in one place, without changes to agent code.

Galileo websiteGalileo vs ArizeGalileo vs BraintrustGalileo vs Confident AIGalileo vs DatadogGalileo vs FiddlerGalileo vs HeliconeGalileo vs HoneyHiveGalileo vs LangfuseGalileo vs LangSmithGalileo vs LogfireGalileo vs Maxim AIGalileo vs OpikGalileo vs RaindropGalileo vs W&B Weave

What is HoneyHive?

HoneyHive is a hosted agent observability and evaluation platform built on OpenTelemetry, covering tracing, offline experiments, online evaluations, human annotation, monitoring and prompt versioning.

Best for: Teams, including those in regulated industries, that want a hosted, OpenTelemetry-based platform combining agent tracing, offline and online evaluation, human annotation and monitoring, with a self-hosted option on Enterprise.

Open source: Partly. Its SDKs and tools are MIT-licensed; the platform itself is proprietary.

Acts during a run: No. HoneyHive does not document blocking, guardrails or approvals on live agent actions. Its Policies feature sets evaluation and monitoring standards, not run-time enforcement.

HoneyHive websiteHoneyHive vs ArizeHoneyHive vs BraintrustHoneyHive vs Confident AIHoneyHive vs DatadogHoneyHive vs FiddlerHoneyHive vs GalileoHoneyHive vs HeliconeHoneyHive vs LangfuseHoneyHive vs LangSmithHoneyHive vs LogfireHoneyHive vs Maxim AIHoneyHive vs OpikHoneyHive vs RaindropHoneyHive vs W&B Weave

What is Confident AI?

Confident AI is an evaluation and observability platform built around DeepEval, its open-source evaluation framework, covering offline evals, tracing with online evals, human annotation, simulation and red teaming.

Best for: Teams that want a code-first, open-source evaluation framework (DeepEval) with a hosted platform for regression testing, online evals on production traces, human annotation and red teaming.

Open source: Partly. DeepEval and the confident-trace SDK are Apache-2.0. The Confident AI platform is proprietary, and self-hosting requires an Enterprise licence.

Acts during a run: No. Confident AI does not document blocking or approval of live agent actions. Its threshold checks run on recorded production data over a trailing 24-hour window.

Confident AI websiteConfident AI vs ArizeConfident AI vs BraintrustConfident AI vs DatadogConfident AI vs FiddlerConfident AI vs GalileoConfident AI vs HeliconeConfident AI vs HoneyHiveConfident AI vs LangfuseConfident AI vs LangSmithConfident AI vs LogfireConfident AI vs Maxim AIConfident AI vs OpikConfident AI vs RaindropConfident AI vs W&B Weave

What is Datadog?

Datadog Agent Observability, formerly LLM Observability, is Datadog's module for tracing, evaluating and running experiments on LLM applications and agents, alongside Datadog's APM and infrastructure data.

Best for: Teams already using Datadog for APM and infrastructure who want LLM and agent traces, evaluations and costs in the same platform, correlated with backend services.

Open source: Partly. The platform is proprietary SaaS; instrumentation SDKs such as dd-trace-py are open source. There is no self-hosted option.

Acts during a run: Partly. Agent Observability monitors and evaluates but does not block. Blocking prompts, responses and tool calls needs AI Guard, a separate Datadog product in limited availability, billed per token scanned.

Datadog websiteDatadog vs ArizeDatadog vs BraintrustDatadog vs Confident AIDatadog vs FiddlerDatadog vs GalileoDatadog vs HeliconeDatadog vs HoneyHiveDatadog vs LangfuseDatadog vs LangSmithDatadog vs LogfireDatadog vs Maxim AIDatadog vs OpikDatadog vs RaindropDatadog vs W&B Weave

What is Fiddler?

Fiddler is a commercial observability, evaluation and guardrails platform that covers classic ML models, LLM applications and agents in one place.

Best for: Enterprises, often in regulated sectors, that want one vendor for monitoring both traditional ML models and LLM/agent applications, with self-hosted deployment and low-latency guardrails.

Open source: Partly. The platform is proprietary; its Python client and Claude Code plugin are Apache-2.0.

Acts during a run: Partly. Fiddler Guardrails score content in real time for your application to act on, and can block inline through a third-party AI gateway. There are no approvals or tool-call policies.

Fiddler websiteFiddler vs ArizeFiddler vs BraintrustFiddler vs Confident AIFiddler vs DatadogFiddler vs GalileoFiddler vs HeliconeFiddler vs HoneyHiveFiddler vs LangfuseFiddler vs LangSmithFiddler vs LogfireFiddler vs Maxim AIFiddler vs OpikFiddler vs RaindropFiddler vs W&B Weave

What is Logfire?

Pydantic Logfire is an OpenTelemetry-based observability platform from the team behind Pydantic, tracing whole applications, including LLM and agent calls, with evals, prompt versioning and an AI gateway built in.

Best for: Python-heavy teams, especially those using Pydantic AI, who want LLM and agent traces in the same OpenTelemetry view as the rest of their application, with evals, prompt versioning and a gateway from one vendor.

Open source: Partly. The SDKs, pydantic-evals and Pydantic AI are MIT-licensed; the Logfire platform is closed source. Self-hosting is Enterprise only.

Acts during a run: Partly. Model calls routed through its AI gateway can be flagged, redacted or blocked, and spend caps stop requests over budget. Tool actions outside the gateway are not covered.

Logfire websiteLogfire vs ArizeLogfire vs BraintrustLogfire vs Confident AILogfire vs DatadogLogfire vs FiddlerLogfire vs GalileoLogfire vs HeliconeLogfire vs HoneyHiveLogfire vs LangfuseLogfire vs LangSmithLogfire vs Maxim AILogfire vs OpikLogfire vs RaindropLogfire vs W&B Weave

What is Opik?

Opik is an open-source (Apache-2.0) tracing, evaluation and monitoring platform for LLM applications and agents from Comet, available self-hosted or as a hosted cloud.

Best for: Teams that want an open-source, self-hostable tracing and evaluation stack with online LLM-as-judge rules, prompt optimisation and broad framework coverage, and a low-cost cloud option.

Open source: Yes. The core platform, including tracing, evaluation, the UI, backend and SDKs, is Apache-2.0 and free to self-host.

Acts during a run: Partly. Opik guardrails run as a blocking check that your code must call and handle. There are no approval workflows for agent actions.

Opik websiteOpik vs ArizeOpik vs BraintrustOpik vs Confident AIOpik vs DatadogOpik vs FiddlerOpik vs GalileoOpik vs HeliconeOpik vs HoneyHiveOpik vs LangfuseOpik vs LangSmithOpik vs LogfireOpik vs Maxim AIOpik vs RaindropOpik vs W&B Weave

What is Raindrop?

Raindrop is a hosted monitoring platform for AI agents in production that classifies events with custom signals, groups recurring failures into issues and compares changes on live traffic.

Best for: Teams with an agent already in production who want to find recurring failures in real user interactions, track defined behaviours over time and compare changes on live traffic, rather than run pre-release eval suites.

Open source: Partly. Its local debugger, Workshop, and several SDKs are MIT-licensed; the Raindrop Cloud platform is proprietary.

Acts during a run: No. Raindrop analyses events after they arrive and alerts on issues. It does not document blocking, guardrails or approvals on live agent actions.

Raindrop websiteRaindrop vs ArizeRaindrop vs BraintrustRaindrop vs Confident AIRaindrop vs DatadogRaindrop vs FiddlerRaindrop vs GalileoRaindrop vs HeliconeRaindrop vs HoneyHiveRaindrop vs LangfuseRaindrop vs LangSmithRaindrop vs LogfireRaindrop vs Maxim AIRaindrop vs OpikRaindrop vs W&B Weave

What is Maxim AI?

Maxim AI is a hosted platform for simulating, evaluating and tracing AI agents, including voice agents, sold alongside Bifrost, its Apache-2.0 AI gateway.

Best for: Teams that want pre-release simulation (including voice agents) and evaluation run by product and engineering together, with production tracing and an optional self-hosted gateway in the same vendor.

Open source: Partly. The Bifrost gateway and the SDKs are Apache-2.0; the simulation, evaluation and observability platform is proprietary.

Acts during a run: Yes, through the Bifrost gateway: guardrails check inputs, outputs and MCP tool-call arguments and results, and can block, redact or transform content. Guardrails are a Bifrost Enterprise feature.

Maxim AI websiteMaxim AI vs ArizeMaxim AI vs BraintrustMaxim AI vs Confident AIMaxim AI vs DatadogMaxim AI vs FiddlerMaxim AI vs GalileoMaxim AI vs HeliconeMaxim AI vs HoneyHiveMaxim AI vs LangfuseMaxim AI vs LangSmithMaxim AI vs LogfireMaxim AI vs OpikMaxim AI vs RaindropMaxim AI vs W&B Weave

What is W&B Weave?

W&B Weave is a tracing, evaluation and monitoring toolkit for LLM applications and agents from Weights & Biases, now part of CoreWeave and sold through CoreWeave Forge.

Status: Weights & Biases acquired by CoreWeave; W&B hosted accounts moved to CoreWeave Forge in September 2026

Best for: Teams already using Weights & Biases or CoreWeave for model training who want LLM and agent tracing, evaluations and production monitoring in the same platform.

Open source: Partly. The Weave repository is Apache-2.0, but self-hosting Weave needs a W&B licence and an existing W&B platform deployment.

Acts during a run: Partly. Guardrails are scorers called from Python application code that can block or modify inputs and outputs. The TypeScript SDK does not support them, and there are no approvals on agent actions.

W&B Weave websiteW&B Weave vs ArizeW&B Weave vs BraintrustW&B Weave vs Confident AIW&B Weave vs DatadogW&B Weave vs FiddlerW&B Weave vs GalileoW&B Weave vs HeliconeW&B Weave vs HoneyHiveW&B Weave vs LangfuseW&B Weave vs LangSmithW&B Weave vs LogfireW&B Weave vs Maxim AIW&B Weave vs OpikW&B Weave vs Raindrop

§06 / COMPARE ANY TWOhead to head: pair by pair

How do two platforms compare directly?

Each pair page compares the two vendors neutrally, with a capability table generated from the same research as this page and Prefactor shown alongside for reference.

§07 / WHERE PREFACTOR FITSdisclosure: we publish this page

Where does Prefactor fit?

Prefactor is an agent evaluation platform for teams building AI agents: it observes every agent run from development to production, evaluates whether the agent did its job, and shows how to improve it. It can also act on what it finds during the run: runtime policies on tool calls and data access, approval holds for risky actions, and a kill switch scoped to a run, an agent or a team. Among the 15 platforms above, only Galileo and Maxim AI offer comparable controls on live agent actions.

It has gaps too: no prompt playground or prompt registry, a hosted platform with self-hosting only for enterprise deployments, SOC 2 Type II still in progress, and a free tier of 5,000 spans a month, smaller than several above. If those matter more than acting on a failing run, one of the other platforms is the better fit.

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§08 / HOW WE REVIEWEDchecked: 20 October 2026

How was this comparison made?

Each vendor was researched on 20 October 2026 against its own documentation, pricing page, changelog and GitHub repositories, with third-party sources used only for ownership changes. A capability counts as yes only where the vendor documents it, partial where it is limited (for example to model calls, one plan or a preview), and no where it is absent or not stated. The full dataset, with a source link for every value, is available as JSON. Vendors ship quickly; check anything decisive on their own pages.

§09 / QUESTIONSfaq: common questions

Common questions about agent observability platforms

What is the best agent observability and evaluation platform?
There is no single best one; the right choice depends on hosting, stack and whether you need to act during a run. As of 20 October 2026, Prefactor suits teams that need every production run scored and the ability to hold or stop a failing action, Langfuse and Opik suit teams that want open source and free self-hosting, LangSmith suits LangChain teams, and Braintrust suits an experiment-led eval loop. Galileo and Maxim AI are the other platforms here that can act during a run.
What is Prefactor?
Prefactor is an agent evaluation platform for teams building AI agents: it observes every agent run from development to production, evaluates whether the agent did its job, and shows how to improve it. It can also act on what it finds: runtime policies on tool calls and data access, approval holds for risky actions, and a kill switch for a run, an agent or a team. As of 20 October 2026, its free tier includes 5,000 spans a month.
What is the difference between agent observability and agent evaluation?
Observability records what an agent did: every model call, tool call and step, with inputs, outputs, timing and cost. Evaluation judges whether it did the job, using LLM judges, code checks or human review, before release and on production traffic. Most platforms on this page now do both. Prefactor is built around evaluation and acting on the result; others differ in how far they go and whether they can act on a failing score.
Which agent observability platforms are open source?
As of 20 October 2026, Langfuse (MIT, apart from licensed add-ons), Comet Opik (Apache-2.0) and Helicone (Apache-2.0, in maintenance mode) publish their platforms as open source. Arize Phoenix is source-available under the Elastic License 2.0. Prefactor publishes its deterministic agent evals package under Apache-2.0, and most others open-source their SDKs only.
Which platforms can block a bad agent action?
As of 20 October 2026, Prefactor (runtime policies, approval holds and a kill switch), Galileo (Agent Control, which checks model and tool inputs and outputs) and Maxim AI (guardrails in its Bifrost gateway, Enterprise plan). Several others offer partial controls, mostly on model calls or content. The rest evaluate after the fact.
Which agent observability vendors were acquired?
Weights & Biases (Weave) by CoreWeave in 2025; Langfuse by ClickHouse in January 2026; Helicone by Mintlify in March 2026, which put it into maintenance mode; Galileo by Cisco in May 2026, now Splunk Agent Observability; and Arize by Dynatrace, completed on 1 October 2026. Prefactor is independent.
Which agent observability platform has the largest free tier?
As of 20 October 2026, self-hosting Langfuse or Opik is free with no usage cap beyond your own infrastructure. On hosted plans, Logfire's free plan includes 10M records a month, Langfuse's Hobby plan 50k units, Datadog's 40K LLM spans, Arize AX and Opik Cloud 25k spans each, and Prefactor's Dev tier 5,000 spans. Units differ, so compare on your own volumes.
Is Helicone still available?
Helicone's open-source code can still be self-hosted, but as of 20 october 2026 new cloud sign-ups have been disabled since March 2026 and the product has been in maintenance mode, limited to patches, bug fixes and new model support. On 19 October 2026 it said it is no longer part of Mintlify; no new owner has been named.

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