8 LangSmith alternatives for startups: open source, self-hosted and cheaper (2026)

This post compares eight LangSmith alternatives on license, self-hosting, price and features. For each alternative to LangSmith, it lists what the tool adds and what it lacks.

The short answer

• Open source and free to self-host: Langfuse, AcruxCore, Opik, MLflow and Laminar.
• Tracing, prompts, evals and a gateway in one open-source tool: AcruxCore or MLflow.
• Evals first, hosted for you: Braintrust.

LangSmith competitors at a glance

License and hosting

Tool	License	Self-host	Hosted free plan	Cheapest paid plan	Data kept on the paid plan
LangSmith	Closed source	Enterprise plan only	Developer: 5,000 traces, 1 seat, 14 days	Plus: $39 per seat a month	14 days
Langfuse	MIT core; enterprise (ee/) folders commercial	Free	Hobby: 50,000 units, 2 users, 30 days	Core: $29 a month, unlimited users	90 days
AcruxCore	Apache-2.0	Free	Free; span content kept 90 days	None; the hosted plan is free	Not applicable
Opik	Apache-2.0	Free	25,000 spans a month, 10 members, 60 days	Pro: $19 a month, 50 members	60 days
MLflow	Apache-2.0	Free	None outside Databricks	Through Databricks	You decide
Laminar	Apache-2.0	Free	1 GB, 1 seat, 7 days	Starter: $30 a month, unlimited seats	30 days
Arize Phoenix	Elastic License 2.0	Free	Arize AX Free: 25,000 spans, 15 days	Arize AX Pro: $50 a month	30 days
Braintrust	Closed source	Enterprise plan only	1 GB, unlimited users, 14 days	Pro: $249 a month	30 days
W&B Weave	SDK Apache-2.0; server not published	Needs W&B Self-Managed and a Weave license	1 GB a month, 5 seats	Pro: from $60 a month, 10 seats	Not published

Features

Tool	Prompt versions	Gateway (your model calls pass through it)	Evals on datasets	Evals on live traffic	Status in 2026
LangSmith	Yes	Beta	Yes	Yes	Active
Langfuse	Yes	No	Yes	Yes	Active; owned by ClickHouse since January 2026
AcruxCore	Yes	Yes	Yes	Yes	Active; public since August 2026
Opik	Yes	Beta, for development and testing	Yes	Yes	Active
MLflow	Yes	Yes	Yes	Yes	Active; a Linux Foundation project
Laminar	No	No	Yes	Signals (rules in plain English)	Active
Arize Phoenix	Yes	No	Yes	Yes	Active
Braintrust	Yes	Yes, hosted, in public preview	Yes	Yes	Active
W&B Weave	Partial	No	Yes	Yes	Active; W&B is owned by CoreWeave

A unit on Langfuse is one trace, one step inside a trace, or one score. A span is one step inside a trace. Opik, Phoenix and Braintrust count spans or gigabytes, so their free plans are not directly comparable with LangSmith's 5,000 traces. Closed source means the vendor publishes no server code.

Why teams look for a LangSmith alternative

• Every seat costs money. The Plus plan costs $39 per seat a month. Three people pay $117 a month before they pay for extra traces.
• Traces are kept 14 days. Base traces on Free and Plus are deleted after 14 days. Extended traces are kept 180 days for an extra fee.
• Self-hosting needs Enterprise. LangSmith self-hosting is an add-on to the Enterprise plan. Self-hosted LangSmith runs on Kubernetes with ClickHouse, PostgreSQL and Redis. It needs a license key from sales.
• The platform is not open source. The SDKs are MIT. The server ships only as container images that need a license key.

LangSmith does not need LangChain for tracing. Its traceable decorator and its OpenTelemetry endpoint work with any code.

Sources: LangSmith pricing, billing, self-hosting and OpenTelemetry pages.

How we picked

• The tool does LangSmith's core jobs: tracing, and at least one of prompts or evals.
• The tool is active today. Each tool had a release or a commit in October 2026.
• The price is public, or the tool is free to self-host.
• Every fact comes from the vendor: the pricing page, the docs, the license file or the repository's compose file, read on 17 October 2026. We do not use other comparison lists as sources.

Open-source LangSmith alternatives (free to self-host)

These five tools use a license approved by the Open Source Initiative. You can run every one of them on your own servers without paying.

1. Langfuse

Langfuse vs LangSmith: Langfuse is open source and free to self-host, and LangSmith is neither.

Best for: teams that want the open-source tool with the largest community for tracing, prompts and evals.

	Langfuse	LangSmith
License	MIT core; enterprise (ee/) folders under a commercial license	Closed source
Self-host	Free: web, worker, Postgres, ClickHouse, Redis, S3 storage	Enterprise plan only
Cheapest paid plan	Core: $29 a month, 100,000 units, unlimited users, 90 days	Plus: $39 per seat a month, 10,000 traces, 14 days
Gateway	No	Beta

Where Langfuse differs

• Langfuse charges one flat price for the whole team on Core. LangSmith charges per seat.
• Langfuse keeps data 90 days on Core. LangSmith keeps base traces 14 days on Plus.
• Langfuse has the largest community here: 35,957 GitHub stars.
• Datasets, experiments, LLM-as-judge on live traces and review queues are all in the free self-hosted version.

Limits of Langfuse

• Langfuse has no gateway. The Langfuse docs use LiteLLM as the gateway.
• A self-hosted install runs four data stores: Postgres, ClickHouse, Redis and S3.
• Audit logs, project-level roles and retention controls need an enterprise license, even when you self-host.

We compared both tools on one app in Langfuse vs LangSmith.

Sources: license, pricing, self-host pricing, compose file, ClickHouse acquisition.

2. AcruxCore

AcruxCore vs LangSmith: both cover prompts, tracing and evals. AcruxCore is Apache-2.0 and free to self-host, and its gateway sends your model calls to the provider.

Best for: small teams that want prompts, a gateway, traces and evals in one self-hosted app.

	AcruxCore	LangSmith
License	Apache-2.0, no enterprise folder	Closed source
Self-host	Free: Postgres, Redis, API, worker, web	Enterprise plan only
Cheapest paid plan	None; the hosted plan is free to use	Plus: $39 per seat a month
Gateway	Yes	Beta

Where AcruxCore differs

• The gateway is part of the product. It holds your provider keys, caches responses, falls back to a second model, and stops calls at a spend budget or a rate limit.
• You define the tools a model can call and keep versions of them. AcruxCore runs a tool when your code calls its API.
• Roles and the audit log are free in every AcruxCore install. LangSmith keeps custom roles for Enterprise.
• Self-hosting needs two data stores, Postgres and Redis, with no ClickHouse.

Limits of AcruxCore

• The AcruxCore repository went public in August 2026 and has 11 GitHub stars.
• AcruxCore has no SAML or OIDC single sign-on. Sign-in is email or Google.
• The gateway supports OpenAI, Anthropic, Gemini and OpenAI-compatible APIs. The SDKs are Python and TypeScript only.

Our longer comparison is AcruxCore vs LangSmith.

Sources: license, compose file, pricing.

3. Opik

Opik vs LangSmith: Opik is Apache-2.0 from end to end and has the cheapest paid plan here.

Best for: teams that want open-source evals and automatic prompt optimization.

	Opik	LangSmith
License	Apache-2.0	Closed source
Self-host	Free: MySQL, Redis, ClickHouse, ZooKeeper, MinIO, three app services	Enterprise plan only
Cheapest paid plan	Pro: $19 a month, 100,000 spans, up to 50 members, 60 days	Plus: $39 per seat a month
Gateway	Beta, for development and testing	Beta

Where Opik differs

• Opik ships an optimizer package that rewrites prompts and agents for you, with six optimization algorithms.
• Opik has guardrails for PII, topics and prompt injection.
• Opik's free cloud plan allows 10 members. LangSmith's free plan allows 1 seat.

Limits of Opik

• The self-hosted version has no user management.
• A self-hosted install runs five data stores: MySQL, Redis, ClickHouse, ZooKeeper and MinIO.
• The Opik docs describe the Opik gateway as beta, for development and testing.

Our comparison: AcruxCore vs Opik.

Sources: README and license, pricing, self-hosting, compose file, gateway, optimizer.

4. MLflow

MLflow vs LangSmith: MLflow is an Apache-2.0 ML platform with tracing, a prompt registry, judges and a gateway in one server.

Best for: teams that already run MLflow for classic machine learning.

	MLflow	LangSmith
License	Apache-2.0, Linux Foundation	Closed source
Self-host	Free: pip install mlflow and mlflow server on SQLite; Postgres and S3 storage for production	Enterprise plan only
Cheapest paid plan	No public price; the managed version comes with Databricks	Plus: $39 per seat a month
Gateway	Yes	Beta

Where MLflow differs

• MLflow can run as one Python process with a SQLite file, with no Docker.
• The gateway splits traffic by weight, falls back to another model, and rejects calls over a USD budget.
• Judges can score live traces with no code change, and review queues assign traces to people.
• The same server holds your training runs and model registry.

Limits of MLflow

• MLflow has no hosted plan of its own. The managed version needs a Databricks workspace.

Our comparison: AcruxCore vs MLflow.

Sources: license, GenAI docs, self-hosting, compose file, managed MLflow.

5. Laminar

Laminar vs LangSmith: Laminar is open-source tracing built for agents, with SQL over your traces.

Best for: teams that run agents with many steps, or agents that use a browser.

	Laminar	LangSmith
License	Apache-2.0; Signals and alerts need a license key when self-hosted	Closed source
Self-host	Free: Postgres, ClickHouse, Quickwit, frontend, app server	Enterprise plan only
Cheapest paid plan	Starter: $30 a month, 3 GB, unlimited seats, 30 days	Plus: $39 per seat a month, 14 days
Gateway	No	Beta

Where Laminar differs

• Laminar replays a browser agent's session as video, next to the matching steps of the trace.
• You can query traces, spans and metrics with SQL.
• Signals are rules written in plain English, such as "agent is stuck in a loop". Laminar checks every trace against these rules.

Limits of Laminar

• Laminar has no prompt management, so you need another tool to version prompts.
• Laminar's free cloud plan keeps data 7 days, and Starter keeps data 30 days.

Our comparison: AcruxCore vs Laminar.

Sources: repository, compose file, pricing.

Source-available: Arize Phoenix

6. Arize Phoenix

Phoenix vs LangSmith: Phoenix is free to self-host with no feature limits. Its license, the Elastic License 2.0, is not approved by the Open Source Initiative.

Best for: engineers who want free self-hosted tracing and evals built on OpenTelemetry.

	Arize Phoenix	LangSmith
License	Elastic License 2.0	Closed source
Self-host	Free: one container, SQLite or Postgres	Enterprise plan only
Cheapest paid plan	Arize AX Pro: $50 a month, 50,000 spans, unlimited users, 30 days	Plus: $39 per seat a month
Gateway	No	Beta

Where Phoenix differs

• The Elastic License forbids selling Phoenix to others as a hosted service. Running Phoenix for your own team is allowed.
• Self-hosting takes one container, or pip install arize-phoenix and phoenix serve, with SQLite.
• Tracing uses OpenInference, Arize's OpenTelemetry conventions, so any OpenTelemetry language can send spans.
• Prompts have versions and tags, and the playground replays a traced model call.

Limits of Phoenix

• The hosted plans are small: 25,000 spans on Free and 50,000 on Pro.
• On the hosted Arize AX plans, single sign-on and audit logs need Enterprise.

Our comparison: AcruxCore vs Phoenix.

Sources: license, self-hosting, compose file, pricing.

Hosted, closed-source alternatives

Braintrust and W&B Weave publish no server code, like LangSmith. Self-hosting either one needs an enterprise contract.

7. Braintrust

Braintrust vs LangSmith: both are closed source and hosted. Braintrust charges a flat price with unlimited users, and LangSmith charges per seat.

Best for: teams whose main work is evals and experiments.

	Braintrust	LangSmith
License	Closed source; SDKs Apache-2.0	Closed source; SDKs MIT
Self-host	Enterprise only; your data stays in your cloud, Braintrust hosts the UI	Enterprise only
Cheapest paid plan	Pro: $249 a month, 5 GB, unlimited users, 30 days	Plus: $39 per seat a month
Gateway	Yes, hosted, in public preview	Beta

Where Braintrust differs

• Loop is an agent inside Braintrust. It reads your logs and experiments, then edits prompts, scorers and datasets after you approve.
• The gateway caches responses for up to 7 days and falls back to another provider on errors.
• Braintrust gives Pro free for 6 to 12 months to startups that qualify. LangSmith gives up to $10,000 in credits to startups with venture funding.

Limits of Braintrust

• Braintrust's free plan keeps data 14 days.
• Prompt environments need Pro.
• The Braintrust gateway has no uptime guarantee (SLA) while it is in preview.

Our comparison: AcruxCore vs Braintrust.

Sources: pricing, self-hosting, gateway, Loop.

8. W&B Weave

Weave vs LangSmith: Weave puts LLM traces and evals next to Weights & Biases experiment tracking.

Best for: teams that already use Weights & Biases.

	W&B Weave	LangSmith
License	SDK Apache-2.0; the trace server is not published	Closed source
Self-host	Needs W&B Self-Managed, a Weave license from W&B support, Kubernetes and a ClickHouse cluster	Enterprise plan only
Cheapest paid plan	Pro: from $60 a month, 10 seats, 1.5 GB of traces a month	Plus: $39 per seat a month
Gateway	No	Beta

Where Weave differs

• One subscription covers W&B experiment tracking and Weave traces.
• Monitors run LLM-judge checks, such as hallucination, on every production trace.
• The playground compares models side by side, using provider keys stored as team secrets.

Limits of Weave

• Pro includes 1.5 GB of traces a month.
• The pricing page does not state how long traces are kept.

Sources: pricing, README, self-managed Weave, monitors, CoreWeave acquisition.

Tools other lists still recommend

Older lists of LangSmith alternatives still include these five tools. Their status on 17 October 2026:

• Helicone was acquired by Mintlify in March 2026. The service runs in maintenance mode: it gets security fixes, bug fixes and new models, but no new features. (source)
• Portkey was acquired by Palo Alto Networks in May 2026. The open-source gateway repository has had no merged code since 25 May 2026. (source)
• Humanloop shut down on 8 September 2025. (source)
• Traceloop announced in March 2026 that it is joining ServiceNow. Its OpenLLMetry library stays open source and active. (source)
• Galileo was acquired by Cisco and is now sold as Splunk Agent Observability. It is closed source. (source)

Which LangSmith alternative should you pick?

Best LangSmith alternative for a startup

• AcruxCore if you want one self-hosted app for prompts, gateway, traces and evals, and the hosted plan is free to use.
• Opik if you want a paid cloud plan: $19 a month for up to 50 members.
• Langfuse if you want the largest open-source community and $29 a month for unlimited users.

Best free LangSmith alternative

• AcruxCore, MLflow or Arize Phoenix to self-host without ClickHouse. AcruxCore runs on Postgres and Redis. MLflow and Phoenix each run as one Python process on SQLite. Phoenix's license forbids selling it as a hosted service.
• Opik for a free cloud plan that keeps data 60 days for up to 10 members.

Self-hosted LangSmith alternatives for regulated teams

• Langfuse and Opik keep every trace on your servers. Both also need ClickHouse, an analytics database you must run and back up.
• AcruxCore keeps every trace on your servers on Postgres and Redis.
• MLflow keeps every trace on your servers on Postgres and an S3-compatible store.

LangSmith alternatives for enterprises

• Braintrust Enterprise adds SAML single sign-on, custom roles and an SLA.
• Langfuse Enterprise adds audit logs, automatic user provisioning (SCIM) and an uptime SLA.

FAQ

Is LangSmith open source?

No. The LangSmith SDKs are MIT-licensed, but the platform has no public source code. The self-hosted version ships as container images that need a license key.

Is LangSmith free?

The Developer plan is free for 1 seat and 5,000 base traces a month, kept for 14 days. The Plus plan costs $39 per seat a month. (pricing)

Can you self-host LangSmith?

Only on the Enterprise plan. Self-hosting is an add-on to that plan and needs a license key from sales. It runs on Kubernetes with ClickHouse, PostgreSQL and Redis.

Does LangSmith need LangChain?

Not for tracing. The traceable decorator and the OpenTelemetry endpoint work without LangChain.

What is the best open-source LangSmith alternative?

Langfuse has the most GitHub stars of the open-source alternatives: 35,957. AcruxCore and MLflow add a gateway to tracing, prompts and evals. Opik adds automatic prompt optimization.

Related posts

• Langfuse vs LangSmith: one app run end to end on both.
• 9 LLM observability tools tested hands-on: nine tools tested hands-on, with screenshots of each.
• AcruxCore vs Langfuse vs LangSmith: the same app run on all three.
• LangSmith hands-on walkthrough: every LangSmith screen, step by step.
• 8 best Langfuse alternatives for startups: the same comparison, starting from Langfuse.
• Quickstart: sign up for AcruxCore and send a first trace.
• Self-hosting AcruxCore: the docker compose setup.