Arize Phoenix is free, with no paid plan attached. Google Stax is free, with no paid plan attached. Both are listed under LLM Eval & Observability, so this is a like-for-like comparison. Neither is ranked above the other — Flocci carries no sponsored placement.
Arize Phoenix is free, with no paid plan attached and is listed for fully open-source, self-hostable with zero setup via `uvx` (pip/conda also supported). Google Stax is free, with no paid plan attached and is listed for build evals with human raters or LLM autoraters on your own data. Both sit in LLM Eval & Observability.
Neither — Arize Phoenix and Google Stax are both free, so the choice comes down to capability rather than cost. Both entries list what they uniquely do above.
Choose Arize Phoenix if you need fully open-source, self-hostable with zero setup via `uvx` (pip/conda also supported); choose Google Stax if you need build evals with human raters or LLM autoraters on your own data. Flocci AI Tools does not rank one above the other — it shows both feature sets side by side and lets the requirement decide.
| Arize Phoenix | Google Stax | |
|---|---|---|
| Pricing tier | Free | Free |
| Free to start | Yes | Yes |
| Category | AI Models & Local Execution | AI Models & Local Execution |
| Type | LLM Eval & Observability | LLM Eval & Observability |
| Listed capabilities |
|
|
| Tags | arize phoenix, llm observability open source, tracing, evaluation, rag debugging, free | google stax, llm evaluation tool, free prompt evaluation, llm as judge autoraters, compare llm prompts |
| Website | phoenix.arize.com | stax.withgoogle.com |
| Full page | Arize Phoenix details → | Google Stax details → |
| Alternatives | Arize Phoenix alternatives → | Google Stax alternatives → |