Five platforms, five different billing units, and one shared question: what does a month of production traffic actually cost on each. LangSmith bills $39/seat on Plus and meters everything else in LangChain Standard Units at $1.00, with base traces retaining 14 days and extended traces 180. Langfuse bills trace units - 50K free on Hobby, 100K included on the $29 Core plan and $8 per extra 100K - and can be self-hosted at any tier. Braintrust bills scored outputs: 10K a month free, then $2.50 per 1,000 on Starter, with 50K at $1.50 per 1,000 once you move to Pro at $249. Arize AX bills signals, spans and ingestion rather than seats - free at 25K spans and 1 GB, $50/mo for 50K spans and 10 GB, and unlimited users and evals on every tier. Helicone bills requests: 10,000 free on Hobby, then $79/mo for Pro with usage-based pricing on top of every paid tier. All prices read from the vendor pages on 2026-10-03.Arize AX is the seat-free option: every tier carries unlimited users, and you pay for signals, spans and ingestion instead of headcount. Helicone is the drop-in option - the lightest install and the narrowest scope. If the question is cost per unit of telemetry rather than cost per engineer, pick Braintrust for the clearest unit economics or Arize AX for seat-free scaling. Pick Langfuse when a real free tier and self-hosting matter, LangSmith when you live in the LangChain ecosystem, and Helicone when you want the fastest install with the least commitment.
Developer is $0/seat with 5K base traces, Plus is $39/seat with 10K, then $1.00 per LSU. Base traces retain 14 days, extended 180, and evaluators auto-upgrade matching traces to the pricier tier. Enterprise (self-hosted or hybrid) is sales-only.
Free tier: Yes
Paid from: $39/seat/mo (Plus) (Trace volume is metered in LangChain Standard Units (LSU) at $1.00/LSU on top of the seat fee; base traces carry 14-day retention, extended traces 180 days, and retention auto-upgrades can raise your bill)
LangSmith is the observability and evaluation platform from the LangChain team: $0/seat with 5K base traces a month, Plus at $39/seat with 10K, then pay-as-you-go at $1.00 per LangChain Standard Unit.
Hobby is free with 50K units and no credit card, 30 days of data access and 2 users. Core at $29/mo includes 100K units with $8 per extra 100K, 90-day access and unlimited users; self-hosting available at every tier.
Free tier: Yes
Paid from: $29/mo (Core) (Usage is billed in units (100K units included on paid tiers, then $8 per additional 100K, lower at volume); a separate self-hosted pricing page exists for on-prem deployments)
Langfuse is the open-source-first LLM observability platform: free Hobby with 50K units a month, Core at $29/mo for 100K units and 90-day retention, Pro at $199/mo with three-year retention, Enterprise at $2,499/mo.
Starter is free with 10K scores, 1 GB and 14-day retention; Pro at $249/mo brings 50K scores at $1.50 per 1K, 5 GB and 30-day retention ($0.50/GB/mo beyond, up to 180 days). No published annual rate.
Free tier: Yes
Paid from: $249/mo (Pro) (Scored outputs are the billing unit (LLM-as-a-judge, autoevals, custom scorers) alongside processed data and model credits; retention beyond 30 days is billed at $0.50/GB/mo up to 180 days on Pro)
Braintrust is the observability and eval platform with the most explicit score pricing in the cluster: Starter is $0 with 10K scores a month, Pro jumps to $249/mo with 50K scores plus cheaper per-1K rates.
AX Free gives 25K spans, 1 GB, 15-day retention and unlimited users and evals; AX Pro at $50/mo doubles that to 50K spans and 10 GB for 30 days. Self-hosted AX is Enterprise-only, but Phoenix is free and open source.
Free tier: Yes
Paid from: $50/mo (AX Pro) (Billed on signals, spans, ingestion volume and retention rather than seats - users and evals are unlimited on every tier; self-hosted deployment is Enterprise-only, while the open-source Phoenix platform is free and local)
Arize AX is the cheapest paid step in the cluster at $50/mo, with a $0 Free tier (25K spans, 1 GB, 15-day retention) and a free open-source sibling in Arize Phoenix for fully local tracing.
Hobby covers 10,000 requests with 1 GB and 7-day retention; Pro at $79/mo adds unlimited seats, HQL and a month of retention. Team is $799/mo with SOC-2 and HIPAA. Now part of Mintlify.
Free tier: Yes · 7-day free trial on Pro and Team
Paid from: $79/mo (Pro) (Requests are the billing unit and usage-based pricing applies on top of every paid tier; storage beyond 1 GB is usage-billed, and Helicone announced it has joined Mintlify)
Helicone is the request-level observability and gateway layer priced per request: Hobby free with 10,000 requests a month, Pro at $79/mo, Team at $799/mo, and usage-based pricing on top.
Bottom line: LangSmith for platform breadth, Langfuse for value and self-hosting, Braintrust when you need published per-score economics, Arize AX when seats and evals must never be billed, and Helicone for one-line request visibility with caching and a gateway. The billing unit matters more than the feature list here: every one of these five charges you for a different thing, so the right pick depends on whether your cost pressure is trace volume, evaluation volume, team size or raw request count.
Langfuse (free Hobby with 50K units a month, no credit card), Braintrust (free Starter with 10K scores and unlimited users), Arize AX (free tier with 25K spans) and Helicone (10,000 requests) all have genuine free tiers. LangSmith Developer is free but capped at one seat and 5K base traces.
Arize AX and Braintrust list unlimited users on every tier, and Helicone Pro and Team are unlimited seats. LangSmith is the outlier: Plus is $39 per seat per month with unlimited seats allowed, so each additional person is charged. Langfuse Core and above are unlimited users.
Arize AX at $50/mo and Langfuse Core at $29/mo are the two cheapest paid steps. Helicone Pro is $79/mo, LangSmith Plus is $39/seat, and Braintrust Pro is $249/mo - the most expensive entry by a wide margin.
Langfuse offers self-hosted deployment with a separate pricing page at every tier, and Arize publishes Phoenix as a free open-source local-first platform (self-hosted AX itself is Enterprise). LangSmith offers self-hosted and hybrid on Enterprise; Braintrust offers on-prem or hosted deployment on Enterprise.
Arize AX keeps 15 days on Free and 30 on Pro, Braintrust 14 days on Starter and 30 on Pro ($0.50/GB/mo beyond, up to 180), Langfuse 30 days on Hobby and 90 on Core with 3 years on Pro, Helicone 7 days on Hobby and 1 month on Pro. LangSmith is the outlier with two tiers: base traces at 14 days and extended at 180, with retention auto-upgrades that can move traces up a tier.