Skip to main content
Same spans, second viewer. Langfuse shows what a call cost; Phoenix lets you score it, replay it, and run experiments against it.
LLM observability sends every LLM trace through Cribl Stream, which fans it out to Langfuse and Splunk. Phoenix is a third leg on that same input. Nothing upstream changed: the apps still emit to the collector, and the collector still decides where spans go.

​
Why a second trace viewer

Langfuse and Phoenix overlap on tracing, but they lean in different directions. Phoenix is not a replacement. Langfuse stays the trace-of-record and keeps the cost view. Phoenix is where you take a bad trace and turn it into a test case.

​
Self-hosting and license

Arize sells a cloud product (Arize AX) that you cannot self-host. Phoenix is the open server underneath it, and it self-hosts as one container plus Postgres. For a homelab, ELv2 costs nothing. The clause to keep in mind is the managed-service one, which applies if you offer your instance to other people. This page is a summary, not legal advice.
Why not Helicone? It is Apache 2.0 and unlimited too, but it is proxy-based. It only sees traffic that passes through its own gateway or SDK, and it has no OTLP intake. Cribl cannot fan out to it, so it would need every producer re-pointed at a second front door. Its standalone gateway repository had no feature commits after July 2025 and was relicensed to GPL-3 that November (checked September 2026). Phoenix fits the existing pipeline; Helicone would replace part of it.

​
Where it sits

The Phoenix leg runs its own Cribl pipeline. It keeps the same guards as the Langfuse leg: drop non-trace signals, drop plumbing spans, trim noise, and redact credentials. It skips the Langfuse-specific attribute rewrites, because Phoenix reads the emitted GenAI attributes as they are. Both pipelines loop over the same lists in the Cribl role, so there is one place to add a span name or a redaction pattern.

​
Reaching it

Phoenix follows the two rules every service in this stack follows.
  • Humans open https://phoenix.<subdomain>/ and sign in through Authelia. Phoenix auto-creates a user on first SSO login, because Authelia already decides who may reach the app.
  • Cribl POSTs to /v1/traces on the same host with a bearer API key minted in Phoenix. That path sits outside the Authelia gate, so an unauthenticated call gets Phoenix’s own 401, never a login redirect.
That API key is the one manual step. Phoenix mints it after first boot, and it goes into OpenBao where the Cribl role reads it. Until it is seeded, the Cribl converge fails loudly rather than rendering an empty credential.

​
Where to go next

LLM observability

The OTLP pipeline Phoenix hangs off.

Pipeline flows

Every ingest leg, including the OTLP fan-out.

ansible-proxmox-ai

Deploys Phoenix beside Langfuse.

AI orchestration stack

The tools whose calls both viewers trace.