Cheapest LLM observability tools
Answer: Among 9 verified LLM observability vendors with a free plan in our dataset (checked through 2026-10-24), our evidence-based free pick is Langfuse: 50k units/mo; all platform features with limits; no card. Paid entry for Langfuse is stated as $29/mo (100k units, +$8/100k). We rank by stated free-plan limits, not invented unit costs.
- Verified free plans in category: 9
- Free pick: Langfuse — 50k units/mo; all platform features with limits; no card
- Pick paid from: $29/mo (100k units, +$8/100k)
- Last verified (pick): 2026-10-24
Langfuse Hobby lists 50k units/month with all platform features (limited) and no card — the broadest verified free LLM tier. Helicone Hobby (10,000 requests, 1 GB) is simpler for gateway-style logging. Arize AX Free (25k spans, 1 GB/mo, no card) and Opik Free Cloud (25k spans/mo) are solid runners-up; LangSmith Developer caps you at 1 seat and 5k base traces, and Lunary now requires payment for new workspaces.
Based only on plan limits recorded from vendor pages.
All verified free plans in LLM observability
| Vendor | Free limits | Paid from | Checked | Source |
|---|---|---|---|---|
| Arize AX / Phoenix | 25k spans/mo; 1 GB/mo; 10 issues/mo; no card. Phoenix is open source | $50/month | 2026-10-24 | source |
| Braintrust | $0/month; $10 credits; free usage for traces, evals and whole team; no card | $249/month | 2026-10-24 | source |
| Helicone | 10,000 free requests; 1 GB storage; 1 seat | $79/mo | 2026-10-24 | source |
| Laminar | $0/month | $30/month then $2/GB | 2026-10-24 | source |
| Langfuse free pick | 50k units/mo; all platform features with limits; no card | $29/mo (100k units, +$8/100k) | 2026-10-24 | source |
| LangSmith | $0/seat; up to 5k base traces/mo; 1 seat | $39/seat/mo (Plus) | 2026-10-24 | source |
| Opik (Comet) | Cloud: 25k spans/month. Open source: $0 | $19/month | 2026-10-24 | source |
| Portkey | 10k recorded logs/month | $49/month (100k logs) | 2026-10-24 | source |
| W&B Weave | $0/mo; Weave ingestion 1 GB/mo | $60/month | 2026-10-24 | source |
Related
Get a free savings estimate for your stack
Modeling LLM observability spend across vendors? The automated audit uses the same verified rates — free estimate, full report $149.
Watch LLM observability pricing weekly
When any of these free tiers shrink, we email you with the source.
Cite this
Copy for AI tools, writers and procurement docs. Attribution requested under CC BY 4.0.
Data: Cheapest LLM observability free tiers as of 2026-10-24. Source: O11y Watch (https://o11y-watch.pages.dev). License: CC BY 4.0. Please attribute "O11y Watch" with a link to https://o11y-watch.pages.dev/.