Comparison · June 2026
SpendProxy vs Langfuse
Langfuse is an open-source (MIT) LLM engineering platform for tracing, evaluations, prompt management, and datasets. It deliberately does not sit in the request path — it observes asynchronously via SDKs and OpenTelemetry. Langfuse joined ClickHouse in January 2026.
What Langfuse is genuinely good at
- ✓All product features MIT-licensed with free unlimited self-hosting
- ✓Deep tracing across whole agent pipelines, not just LLM calls
- ✓Evals, LLM-as-judge, datasets, prompt versioning — the full engineering loop
- ✓Zero added latency by design (never in the request path)
These tools are genuinely complementary: Langfuse watches quality from the sidelines while SpendProxy controls cost inline. Several teams will reasonably run both.
Side by side
| Langfuse | SpendProxy | |
|---|---|---|
| Primary job | Trace, evaluate, and improve LLM applications and agents | Cut LLM spend: billing-accurate cost tracking plus optimization engines that act on traffic |
| Request path | Asynchronous observer — explicitly not a proxy (their own positioning); recommends a gateway like LiteLLM if you need one | Inline proxy — one base-URL change |
| Hosting & data path | Cloud SaaS or free self-host (Postgres + ClickHouse + Redis + S3) | Licensed Docker container inside your VPC. SQLite-local storage. No request data leaves your network. |
| Automatic cost optimization | None — observes and analyzes; cost metrics are exposed for downstream systems to act on | Five engines that take action: prompt cache injection, response dedup, model routing with circuit breaker, budget guardrails, retry-storm suppression. Each runs in off, monitor (log what it would do), or autopilot mode. |
| Cost tracking | Token + USD tracking with breakdowns and a metrics API | Provider-specific billing semantics: cached tokens, reasoning tokens, and streaming priced the way the provider actually bills. |
| Budgets & enforcement | No enforcement — data for external rate-limiting/billing systems | Per route, tag, or API key — warn or hard-block. |
| Provider coverage | SDK/OTel instrumentation, 50+ framework integrations | OpenAI, Anthropic, Google Gemini. Deliberately deep on three providers rather than broad. |
| Source / license | Open source, MIT (enterprise modules licensed separately) | Commercial. Licensed, air-gapped container. |
| Pricing | Free (50K units) · Core $29/mo · Pro $199/mo · Enterprise $2,499/mo · self-host free | $2,500 30-day pilot, then $1,500/mo flat. |
Choose Langfuse when
- →You need evals, tracing, and prompt management for quality work
- →You want zero risk to the request path
- →You want MIT open source and are happy operating the stack
Choose SpendProxy when
- →Your problem is the bill, and analysis alone has not reduced it — SpendProxy sits inline and acts: cache injection, dedup, routing, budget blocking
- →You need spend enforced (hard budget blocks), not just measured
- →Data residency: everything stays in your VPC in one container
See it on your own traffic
30-day pilot inside your VPC. Monitor mode shows exactly what each engine would save before anything changes. If the numbers aren't there, you'll know in week one.
Langfuse facts verified June 2026 against their official documentation. If anything here is out of date, email hi@spendproxy.com and we'll fix it.