Key findings
- LangSmith bills per trace, however many runs it holds. Langfuse bills each trace, observation and score. Arize AX bills spans and gigabytes ingested.
- Deeper agent runs raise Langfuse and Arize AX bills and leave LangSmith's unchanged. At 50 observations per trace, the same traffic costs about US$757 on Langfuse Core and US$8,010 on Arize AX Pro.
- On LangSmith, each trace kept 180 days costs 50% more than a 14-day trace. Langfuse and Arize AX set retention by plan.
- LangSmith Plus charges US$39 per user. Langfuse and Arize AX plans include unlimited users.
For a 10-person team, GILD calculates US$199 to US$369 on Langfuse, US$1,340 on LangSmith Plus and US$1,610 on Arize AX Pro at list price. The gap comes from what each tool meters, so price your own trace shape before you compare plans. Prices are US-dollar list prices from October 12, 2026, with Arize's overage rate from October 25, 2026; on October 28, 2026 Arize's pricing page no longer listed an overage rate.
What each tool bills
LangSmith Plus is US$39 per seat per month with 10,000 base traces included. Each further base trace costs 0.005 LSU, or US$5 per 1,000, and upgrading one to 180-day retention adds 0.0025 LSU. A trace is one execution of the application with all its runs, up to 25,000.
Langfuse Core is US$29 a month with 100,000 units included, then US$8 per 100,000 units, falling in tiers to US$6 above 50 million. A unit is a trace, an observation, or a score.
Arize AX Pro is US$50 a month with 50,000 spans, 10 GB of ingestion and 30-day retention. On October 25, 2026 the tooltips on Arize's pricing page listed US$0.0008 per span past the allowance, which is US$800 per million, and US$3 per extra GB; on October 28, 2026 the page listed no overage rate. The same page in February 2026 listed US$10 per million extra spans and 100 GB included, so an Arize quote from before the change understates today's cost.
A worked month
GILD assumed 10 people who need access and an application that produces 200,000 traces a month, each with 10 observations and 1 evaluator score. On LangSmith Plus that is US$390 in seats plus US$950 for 190,000 billable base traces, US$1,340 in total. If online evaluators upgrade 10% of traces to extended retention, add US$50.
On Langfuse the same month is 2.4 million units. Core costs US$29, plus US$72 for the units from 100,000 to 1 million and US$98 for the next 1.4 million, for US$199 with 90 days of data access. Pro costs US$369 with 3 years.
On Arize AX Pro the same traffic is 2 million spans, 40 times the allowance. At the October 25 rate, GILD's arithmetic is US$50 plus 1,950,000 extra spans at US$0.0008, which is US$1,560, for US$1,610 a month with unlimited users. Ingestion past the Pro allowance adds US$3 per GB on top, and the GB count depends on how large each span's payload is.
| Plan | What is included | Monthly cost |
|---|---|---|
| LangSmith Plus, base retention | 10 seats, 14-day traces | |
| LangSmith Plus, 10% extended | 10 seats, 20,000 traces kept 180 days | |
| Langfuse Core | Unlimited users, 90-day data access | |
| Langfuse Pro | Unlimited users, 3-year data access |
GILD calculation from LangChain and Langfuse list prices, checked Oct 12, 2026; trace counts and shape are assumptions
Depth and seats move the answer
LangSmith's price does not change with trace depth: an agent run with 50 observations costs the same as one with 5. At 50 observations and 1 score per trace, the same 200,000 traces become 10.4 million Langfuse units, about US$757 a month on Core by GILD's calculation, while LangSmith stays at US$1,340. On Arize AX Pro they become 10 million spans, and at the October 25 rate US$50 plus 9,950,000 extra spans at US$0.0008 comes to US$8,010 a month.
LangSmith seat charges rise with each engineer, product manager, or reviewer who needs trace access. Langfuse and Arize AX include unlimited users. Langfuse's MIT-licensed core and Arize Phoenix have no self-hosting license fee. Self-hosted LangSmith requires an Enterprise contract.
What changes the bill after launch
On LangSmith, online evaluators and automation rules upgrade the traces they touch to extended retention by default, and experiments create extended traces. A developer whose code-evaluator experiments filled the extended-trace limit found new experiments blocked. Engine, Fleet, Sandboxes, and LangSmith Deployment add LSU charges on top. On Langfuse, scores from LLM-as-a-judge, annotation queues, and experiments count as units too.
One Hacker News commenter preferred Langfuse because LangSmith bills for seats and per trace and charges more to keep a trace past 14 days. Another canceled Plus and kept opt-in tracing of a fraction of runs on a free organization for debugging. Before you compare plans, measure these four numbers.
- Traces per month, from a week of production traffic.
- Observations and scores per trace, for unit-priced tools.
- Share of traces you must keep at extended retention.
- People who need to read traces.
Methodology
GILD calculated every total from list prices on LangChain's, Langfuse's, and Arize's official pages, checked on October 12, 2026. It also used the Pro overage rates in Arize's pricing-page tooltips, checked on October 25, 2026. Those rates were checked against a stored copy and an Internet Archive capture from February 23, 2026. Trace volume, trace shape, team size, and upgrade share are GILD's assumptions, stated where used. GILD counts each observation as one Arize span, and the Arize totals leave out ingestion past 10 GB because GB per span depends on payload size. The public accounts were opened on October 12, 2026. Accounts published before October 2026 cite US$0.50 per 1,000 base traces, and the totals here use the rates LangChain's pricing page lists on October 12, 2026.
Products in this piece
Sources
- Official documentation
- 9
- Public source
- 4
- LangSmith plans and pricing
- LangSmith docs: Usage and billing (retention tiers and rate limits)
- LangSmith docs: Manage billing and spend limits
- Langfuse pricing
- Langfuse docs: Billable units
- Langfuse self-hosted pricing
- Arize AX pricing
- Internet Archive: Arize AX pricing page as captured Feb 23, 2026
- Arize AX docs: Pricing and usage
- Arize Phoenix docs: License
- LangChain Forum: Not able to delete not used Extended Data Retention traces (Jul 29, 2025)
- Hacker News comment preferring Langfuse over LangSmith (Aug 11, 2025)
- Tyler Norlund, Portfolio issue #1727: remove the paid-LangSmith wiring after cancelling (Sep 28, 2026)