If your primary requirement is “log every LLM request and response for auditing”, my default recommendation today would be Langfuse.
It is purpose-built for LLM applications and gives you much more than raw logs: traces, prompts, model/provider metadata, token usage, latency, costs, evaluations, and debugging. It is also open source and can be self-hosted, which is particularly attractive when audit data contains sensitive prompts/responses.
My shortlist
| Platform | Best for | Audit logging | Self-host | My take |
|---|
| Langfuse | General-purpose LLM observability | ⭐⭐⭐⭐⭐ | ✅ | Best default |
| Arize Phoenix | OpenTelemetry + enterprise observability | ⭐⭐⭐⭐⭐ | ✅ | Best if OTEL matters |
| LangSmith | LangChain/LangGraph applications | ⭐⭐⭐⭐⭐ | ❌ | Best if deeply invested in LangChain |
| Braintrust | Evaluation + quality monitoring | ⭐⭐⭐⭐ | Limited | Excellent for eval-heavy teams |
| Helicone | Simple gateway-based logging | ⭐⭐⭐⭐⭐ | — | Very easy for straightforward request logging |
Phoenix is especially compelling if you already have an OpenTelemetry observability architecture. It captures model calls, retrieval, tool calls and application logic, and supports Python, TypeScript and Java.
For auditing specifically, I'd design the system so the observability platform isn't your only durable audit record:
Application
│
├── LLM request
│
▼
LLM Observability
(Langfuse / Phoenix)
│
├── prompt + response
├── model/provider
├── timestamp
├── user/request ID
├── token usage
├── latency
├── tools/retrieval
└── evaluation metadata
│
▼
Immutable/WORM storage
for long-term audit retention
That distinction matters: observability is optimized for debugging and analysis; compliance-grade audit retention should generally live in controlled, immutable storage as well.
What I'd choose
- Startup / typical production AI application: Langfuse
- Enterprise with existing OpenTelemetry stack: Arize Phoenix
- Almost entirely LangChain/LangGraph: LangSmith
- Quality/evaluation is as important as logging: Braintrust
- Just want a transparent LLM request/response gateway: Helicone
One important consideration: don't blindly log raw prompts and responses. Put a redaction/privacy layer in front of the logger for PII, credentials, API keys, financial information, etc., and establish retention/access policies.
If you tell me your stack (OpenAI/Anthropic/Azure, Python/Node, Kubernetes, AWS/Azure/GCP, compliance requirements such as SOC 2/HIPAA, and approximate requests/day), I can give you a much more specific recommendation and architecture.
For auditing specifically, I'd design the system so the observability platform isn't your only durable audit record:
Application
│
├── LLM request
│
▼
LLM Observability
(Langfuse / Phoenix)
│
├── prompt + response
├── model/provider
├── timestamp
├── user/request ID
├── token usage
├── latency
├── tools/retrieval
└── evaluation metadata
│
▼
Immutable/WORM storage
for long-term audit retention
That distinction matters: observability is optimized for debugging and analysis; compliance-grade audit retention should generally live in controlled, immutable storage as well.
What I'd choose
- Startup / typical production AI application: Langfuse
- Enterprise with existing OpenTelemetry stack: Arize Phoenix
- Almost entirely LangChain/LangGraph: LangSmith
- Quality/evaluation is as important as logging: Braintrust
- Just want a transparent LLM request/response gateway: Helicone
One important consideration: don't blindly log raw prompts and responses. Put a redaction/privacy layer in front of the logger for PII, credentials, API keys, financial information, etc., and establish retention/access policies.
If you tell me your stack (OpenAI/Anthropic/Azure, Python/Node, Kubernetes, AWS/Azure/GCP, compliance requirements such as SOC 2/HIPAA, and approximate requests/day), I can give you a much more specific recommendation and architecture.