LangSmith alternatives for model monitoring

LangSmith is excellent at tracing LangChain/LangGraph applications, prompt versioning, and dataset-based offline evals. It is not designed for continuous provider-side regression monitoring on aliases you don't control. Alternatives by use case: Helicone for OpenAI-style proxy logging and cost/latency dashboards; PromptLayer for prompt registry and template diffing; Phoenix/Arize for embedding drift and RAG eval; Langfuse as an open-source LangSmith analog; Promptfoo for CI-style eval suites; ModelWatch for daily golden-prompt drift detection against the actual provider APIs.

If your pain is "I can't tell whether the model changed or my prompt regressed," that is specifically the ModelWatch lane — fixed-input, fixed-judge, daily, with public per-model scorecards across OpenAI, Anthropic, Google, Meta, Mistral, and DeepSeek.