Our take
Pick Arize AX if agent / ML teams who will stay on AX Free at $0 (10 Signal issues, 25k spans, 1 GB, 15-day retention) while they open a first Signal list, then AX Pro at $50/month when they need 25 issues, 50k spans, or 30-day retention. Pick LangSmith if engineers who already write agent code and will open traces when a run surprises them.
LangChain’s hosted observability and eval
Best for
Arize AX An issue list you start at a public $
LangSmith See what an agent did, then score it
Free plan
Arize AX $0 · no card. 10 Signal issues / month. 25k trace spans / month. 1 GB ingestion. 15-day retention. SaaS. Unlimited users. Unlimited evals. 1 org / 1 space
LangSmith $0 · / seat / month. 1 seat. 5,000 base traces/month, then pay-as-you-go. 7 LSU Fleet allowance/month. Community support
Lowest paid
Arize AX AX Pro $50/mo
LangSmith Plus $39/mo
Coding agent
Arize AX Experiments
LangSmith
Runs where
Arize AX Local or hosted
LangSmith Hosted
Watch out
Arize AX Free Signal caps at 10 issues / month (account-wide, UTC)
LangSmith Traces after 5k / 10k bill in arrears
Last checked
Arize AX 2026-10-23 · arize.com/pricing
LangSmith 2026-10-22 · langchain.com/pricing
agent / ML teams who will stay on AX Free at $0 (10 Signal issues, 25k spans, 1 GB, 15-day retention) while they open a first Signal list, then AX Pro at $50/month when they need 25 issues, 50k spans, or 30-day retention.
Read the Arize AX pageengineers who already write agent code and will open traces when a run surprises them.
Read the LangSmith page