LangSmith vs Arize Phoenix: 2026 comparison

LangSmith and Arize Phoenix in brief

LangSmith and Arize Phoenix help you inspect agent execution and compare results through testing. Both provide web access, an API and a free offering. Their operating frameworks differ clearly: LangSmith is a closed source freemium tool with mixed data hosting, while Phoenix has open code and local hosting. The published feature lists also distinguish LangSmith’s cost and response time monitoring from Phoenix’s explicitly stated response evaluation. Your choice depends on which information you need to track and the hosting and software framework you prefer.

LangSmith : LangSmith examines agent steps and compares results across versions. It serves people who want to create test datasets and monitor the costs and response times of their agents.

Arize Phoenix : Arize Phoenix lets teams developing agents examine execution steps and evaluate response quality. It also supports comparing prompt versions and building datasets to use when testing their systems.

Both meet the same need, which makes the comparison useful. We compare them on 10 verifiable criteria, using the same data as their profiles, collected from official sites.

Comparison table

Criterion by criterion

For each criterion: why it matters, each one's value and who has the edge. A criterion without data on both sides is not decided.

Free tier

A free tier lets you test the tool on your own examples before paying anything. LangSmith : yes. Arize Phoenix : yes. A tie on this point.

Entry price

The first paid plan, per month, gives the minimum cost of regular use; higher plans cost more. LangSmith : $39 per month. Arize Phoenix : not published. Cannot be decided: data missing on one side.

Public API

An API lets you connect the tool to your software, an automation tool or an AI agent. LangSmith : yes. Arize Phoenix : yes. A tie on this point.

Data export

Being able to get your content back avoids lock-in the day you want to switch tools. LangSmith : yes. Arize Phoenix : yes. A tie on this point.

Data hosting

Where data is stored matters for GDPR and client data: the EU or local processing make compliance simpler. LangSmith : several regions. Arize Phoenix : on device. Edge: Arize Phoenix.

Interface languages

More interface languages make the tool easier to roll out across an international team. LangSmith : not published. Arize Phoenix : 1. Cannot be decided: data missing on one side.

Platforms

The more platforms (web, desktop, mobile, extension), the better the tool fits your daily routine. LangSmith : web browser and API. Arize Phoenix : web browser and API. A tie on this point.

Open source

Public code lets you audit the tool, self-host it and keep using it if the publisher changes course. LangSmith : no. Arize Phoenix : yes. Edge: Arize Phoenix.

Track record

A tool launched several years ago has a longer history: less risk of sudden shutdown, more user feedback. LangSmith : launched in 2023. Arize Phoenix : launched in 2023. A tie on this point.

Recognition

The number of reference community lists citing the tool shows how well known it is among practitioners. LangSmith : cited in 3 lists. Arize Phoenix : cited in 2 lists. Edge: LangSmith.

In charts

Our analysis

LangSmith, published by LangChain Inc., lists inspection of agent steps, comparison of results across versions and creation of test datasets. It also documents monitoring of costs and response times. Arize Phoenix, from Arize AI, Inc., describes inspection of execution steps, evaluation of response quality, comparison of prompt versions and preparation of test datasets. Both launched in 2023 and serve a common need to observe behavior and compare outcomes. These feature lists identify relevant differences in emphasis. They do not establish which tool evaluates more accurately, monitors more reliably or provides capabilities that are absent from the other record.

LangSmith uses a freemium model and publishes an entry price of USD 39 per month for Plus, per user, excluding additional consumption. The consumption exclusion means this figure is not a guaranteed total cost. Phoenix uses an open source model, with no published entry price in the supplied record. Both have free offerings, but their limits are not detailed. Their access and transparency scores are 85 and 81 out of 100, respectively, and do not measure quality. LangSmith ranks second out of eighteen and Phoenix fourth, with three and two community list appearances. Those indicators cannot determine your actual budget.

LangSmith lists closed code and mixed data hosting. Phoenix lists open code and local hosting. This is a material distinction if software openness and hosting location guide your decision, but it does not describe all privacy protections. Their documented exports also differ. LangSmith offers CSV, JSONL and an OpenAI fine-tuning preparation format. Phoenix lists Parquet and DataFrame. These outputs let you assess compatibility with existing processes, without proving that either supports a complete migration or exports every type of stored information. Detailed retention policies and data access arrangements are not included in the supplied records for either tool.

LangSmith fits a daily monitoring routine that combines agent steps, version comparisons, costs and response times. Phoenix fits work centered on execution inspection, evaluation and test datasets within a local hosting framework. Both have web interfaces and APIs, although the records do not measure integration effort. LangSmith’s interface languages are undisclosed; Phoenix lists one language and explicitly excludes French. Free offering limits, performance and detailed operating conditions are also unspecified. Your export requirements and hosting preferences therefore provide firmer selection criteria than scores alone. They connect directly to documented differences without requiring assumptions about either tool’s practical quality.

Depending on your situation

The right choice depends on use. For a few common situations, here are the criteria that matter and who wins (LangSmith value / Arize Phoenix value).

Personal use on a tight budget

Neither stands out on the criteria for this situation (free tier (yes / yes), entry price ($39 per month / not published), and interface languages (not published / 1)): decide with a trial.

Business use with client data

Here, Arize Phoenix has the edge: it wins 1 of the 3 criteria that matter in this situation, namely data hosting (several regions / on device), data export (yes / yes), and track record (launched in 2023 / launched in 2023).

Integration with your software

Here, Arize Phoenix has the edge: it wins 1 of the 3 criteria that matter in this situation, namely public api (yes / yes), open source (no / yes), and platforms (web browser and API / web browser and API).

Which one to choose?

Choose LangSmith if…

• you value recognition (cited in 3 lists)

LangSmith is a logical choice when you need explicitly documented cost and response time monitoring alongside agent inspection and version comparisons. Its CSV, JSONL and OpenAI fine-tuning preparation exports may fit your workflow. The published Plus price supports an initial budget estimate, provided you account for per user billing and the additional consumption excluded from the stated monthly amount.

Choose Arize Phoenix if…

• you value data hosting (on device)
• you value open source (yes)

Arize Phoenix fits a preference for open code, local hosting and explicit response evaluation functions. It also suits processes built around Parquet or DataFrame outputs and test datasets. You should account for the stated absence of French in the interface and the unpublished entry price. The documented free offering does not establish the full extent of access or any broader pricing terms.

Strengths and limits of each

LangSmith

• + Free tier to try it
• + Cheaper than its category median
• + Public API

Arize Phoenix

• + Free tier to try it
• + Public API
• + Public source code

The best test is still yours: take three real tasks from your day and give them to both for a week.

What about the others?

If neither suits you, look at Langfuse, Opik, Overmind, MLflow, Respan, and Prisma AIRS AI Gateway — Portkey.

Related comparisons:

• Langfuse vs LangSmith
• Langfuse vs Arize Phoenix

Conclusion

LangSmith documents cost and response time monitoring, a per user subscription price and defined exports. Phoenix emphasizes open code, local hosting and evaluation. Your operating framework and the information you need to inspect or retrieve should guide the choice. Access and transparency scores do not compare software quality. For budgeting, pay particular attention to LangSmith’s additional consumption and the pricing information that remains unpublished for Phoenix in the supplied record.