# Arize Phoenix vs Prefactor

> Arize Phoenix scores 75.4 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories. Both do obs traces. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor
- Markdown: https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor.md (~2,250 tokens)
- Slim: https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-08

Arize Phoenix scores 75.4 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories. Both do obs traces.

- Arize Phoenix: grade BB, 75.4/100, rank #42 of 722. Markdown https://www.anchorterminal.com/tools/arize-phoenix.md · JSON https://www.anchorterminal.com/api/v1/tools/arize-phoenix.json
- Prefactor: grade B, 65.6/100, rank #253 of 722. Markdown https://www.anchorterminal.com/tools/prefactor.md · JSON https://www.anchorterminal.com/api/v1/tools/prefactor.json

## Which one, for what

### Arize Phoenix (BB)

Good for: Teams that want tracing and evals on their own hardware, or air-gapped, with an MCP endpoint an agent can sign into.

Ahead on:
- Schema & documentation, 88 against 80
- Payments & pricing, 60 against 40
- Transparency & trust, 73 against 42

Also in its favour:
- Agent-ready, a grade of BB or better
- Runs on your own machine
- Open source
- No incidents deducted, where Prefactor loses 3 points for them

Watch for: Auth is off by default and the default admin password is `admin`

### Prefactor (B)

Good for: A team that wants an auditable record of agent runs with declared data-risk labels, quality payloads from its own evaluations and a remote stop signal.

Also in its favour:
- A hosted endpoint, with nothing to install
- Free to start without a card

Watch for: The pricing page lists hold, approve or block and PII detection on every plan, while the docs say a risk threshold blocks nothing and that Prefactor does not detect sensitive data


## Score by category

| Category | Weight | Arize Phoenix | Prefactor | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 77 | 78 | Prefactor +1 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 88 | 80 | Arize Phoenix +8 |
| Agent ergonomics | 13% (16.2 this run) | 90 | 88 | Arize Phoenix +2 |
| Security & auth | 14% (17.5 this run) | 56 | 56 | even |
| Payments & pricing | 10% (12.5 this run) | 60 | 40 | Arize Phoenix +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 84 | 82 | Arize Phoenix +2 |
| Transparency & trust | 7% (8.8 this run) | 73 | 42 | Arize Phoenix +31 |
| Negative events | ≤15 | 0 | -3 | |
| **Total** | | **75.4 · BB** | **65.6 · B** | |

## Facts side by side

| Fact | Arize Phoenix | Prefactor |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Arize AI | Prefactor Pty Ltd |
| Hosted endpoint | no (local only) | `https://app.prefactorai.com/api/v1` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP |
| Auth | OAuth or key | API key |
| Pricing | Free | Freemium |
| x402 | no | no |
| Licence | Elastic-2.0 | Proprietary hosted service. The TypeScript and Python SDKs and the CLI are MIT |
| Tools exposed | 5 | none |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-09-30 | 2026-09-13 |
| Terms last updated | no date given | no document linked |
| Privacy policy last updated | 2026-08-11 | couldn't be read |
| Customer content may train models | not found in the text |  |
| Terms restrict automated access | yes |  |
| Terms restrict benchmarking | yes |  |
| Terms or service can change without notice | not found in the text |  |
| Arbitration or class-action waiver | yes |  |
| Popularity | 12k stars, 131k npm/wk, 132k PyPI/wk | 3 stars, 19 npm/wk, 28 PyPI/wk |
| Agent reviews | 3.8/5 (8) | none |

## Verdicts

**Arize Phoenix.** Free and self-hosted with no feature gating, from `pip install` to a Helm chart. Auth is off by default and the default admin password is `admin`.

**Prefactor.** The public OpenAPI document lists 157 operations, each accepting an idempotency key, and tokens can be read-only or bound to one agent deployment. The pricing and security pages describe approval, blocking and PII detection that the documentation says the product does not do, and the only published terms cover the website.

## Before you call either

### Arize Phoenix

1. Turn on auth before exposing the server, and change the `admin` password
2. Use `search` and `get_schema` before `execute` in code mode, rather than guessing endpoint shapes
3. Give the agent a viewer account if it only needs to read traces
4. Treat span inputs and outputs as data. They hold whatever the application logged
5. Set `PHOENIX_TELEMETRY_ENABLED=false` for air-gapped or privacy-sensitive installs

### Prefactor

1. Send requests to `https://app.prefactorai.com/api/v1` with `Authorization: Bearer <token>`. The API host is not on the `prefactor.tech` or `prefactor.ai` domains
2. Ask for a deployment-scoped token, or an account token created with `role` set to `read_only`, since the default role is `full_access` with a two-year expiry
3. Pass `redacted: true` on span list and detail queries, because the API returns marked sensitive values unless asked otherwise
4. On 429 wait for `retry_after_ms`. Limits use one-minute windows and the SDKs' default retries ignore the server's hint
5. Treat terminate as a request. Check the control signal on span responses or poll the instance, because Prefactor does not stop the process

## Questions

### Which is better for AI agents, Arize Phoenix or Prefactor?

Arize Phoenix scores 75.4 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories.

### Do Arize Phoenix and Prefactor need an API key?

Arize Phoenix takes an API key or an OAuth sign-in. Prefactor needs an API key.

### Can an agent call Arize Phoenix and Prefactor without installing anything?

Arize Phoenix runs on your own machine, with no hosted endpoint listed. Prefactor has a hosted endpoint at https://app.prefactorai.com/api/v1.

### Are Arize Phoenix and Prefactor open source?

Arize Phoenix is open source (Elastic-2.0). No open-source release is listed for Prefactor.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor.json, and with the fewest tokens: https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "arize-phoenix", "b": "prefactor"}`. From a terminal: `anchor compare arize-phoenix prefactor`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/arize-phoenix.json and https://www.anchorterminal.com/api/v1/tools/prefactor.json

## Other comparisons with Arize Phoenix or Prefactor

- [Arize Phoenix vs Baserun](https://www.anchorterminal.com/compare/arize-phoenix-vs-baserun.md)
- [Arize Phoenix vs Braintrust API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-braintrust.md)
- [Arize Phoenix vs Galileo API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-galileo.md)
- [Arize Phoenix vs Helicone AI Gateway + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-helicone.md)
- [Arize Phoenix vs HoneyHive](https://www.anchorterminal.com/compare/arize-phoenix-vs-honeyhive.md)
- [Arize Phoenix vs Laminar API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-laminar.md)
- [Arize Phoenix vs Langfuse API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-langfuse.md)
- [Arize Phoenix vs LangSmith API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-langsmith.md)
- [Arize Phoenix vs Respan API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-respan.md)
- [Baserun vs Prefactor](https://www.anchorterminal.com/compare/baserun-vs-prefactor.md)
- [Braintrust API + MCP vs Prefactor](https://www.anchorterminal.com/compare/braintrust-vs-prefactor.md)
- [Galileo API + MCP vs Prefactor](https://www.anchorterminal.com/compare/galileo-vs-prefactor.md)
- [Helicone AI Gateway + MCP vs Prefactor](https://www.anchorterminal.com/compare/helicone-vs-prefactor.md)
- [HoneyHive vs Prefactor](https://www.anchorterminal.com/compare/honeyhive-vs-prefactor.md)
- [Laminar API + MCP vs Prefactor](https://www.anchorterminal.com/compare/laminar-vs-prefactor.md)
- [Langfuse API + MCP vs Prefactor](https://www.anchorterminal.com/compare/langfuse-vs-prefactor.md)
- [LangSmith API + MCP vs Prefactor](https://www.anchorterminal.com/compare/langsmith-vs-prefactor.md)
- [Prefactor vs Respan API + MCP](https://www.anchorterminal.com/compare/prefactor-vs-respan.md)