We're a team of three backend engineers. Our stack is Python/FastAPI with PostgreSQL and Redis. We need to track LLM calls, costs, and latency for our RAG pipeline. Budget is under $200/month.
I've looked at both. Initial take: Vellum is a dev platform with eval workflows. Traceloop is pure observability. They solve different problems.
Key differences for a budget team:
* **Pricing:** Traceloop's free tier is generous (1M spans/month). Vellum's starter is $149/month (10k eval units). Our usage would push Vellum over budget quickly.
* **Core function:** Traceloop instruments your existing code. Vellum wants you to build/run prompts through their SDK.
* **Data:** Traceloop connects to your existing OpenTelemetry data (Jaeger, Tempo). Vellum stores everything in its own cloud.
If you just need monitoring and you're already on OTel, Traceloop is the obvious cost winner. If you need structured eval workflows and don't want to build them yourself, Vellum is a tool you'd pay for.
For us, the decision is simple. We already export traces. Adding Traceloop took an hour:
```python
# pip install opentelemetry-sdk traceloop-sdk
from traceloop.sdk import Traceloop
Traceloop.init(app_name="our_rag_service")
```
Our traces now have LLM cost and latency breakdowns in our existing Grafana dashboards. Zero additional storage cost.
I'm Emma, the solo CS lead at a 70-person B2B SaaS company. We integrate LLMs into our product's help system, and I'm responsible for monitoring the quality and cost. We run a Python/Flask stack with Postgres and have been testing both tools for the last quarter.
Here's my breakdown from managing the budget and working with our two engineers:
1. **Monthly budget reality:** Traceloop's free tier was enough for us for months. We're now on their Pro plan at $49/month for 5 million spans. Vellum's starter is a fixed $149/month for 10k "eval units." One complex RAG test run could consume thousands of those units. For a team of three, Traceloop keeps you under $200 easily; Vellum likely won't.
2. **Integration and lock-in:** Adding Traceloop was adding an OpenTelemetry exporter. It took an afternoon. Vellum required us to route our LLM calls through their SDK and API. This was a weekend project for our dev and created a hard dependency. If Vellum goes down, our features break. If Traceloop goes down, we just lose observability, not function.
3. **Primary function divergence:** This is the biggest choice. Traceloop is a dashboard and alert system for your existing pipeline. You see latency, cost, and traces. Vellum is a prompt engineering and testing workbench. Its monitoring feels like an add-on to its core eval and deployment features. You'd buy Vellum to build prompts, not just to watch them.
4. **Support and docs experience:** As a small team, good docs are critical. Traceloop's docs were straightforward for OpenTelemetry setup. When I emailed them a question about cost attribution, they replied in about 3 hours. Vellum's support was also fast (under 2 hours) but was more sales-engineer led, focused on how to re-architect our flow to use their eval suites.
For your stated need of tracking calls, costs, and latency, I'd pick Traceloop. It's cheaper, fits directly into your existing OTel flow, and doesn't add operational risk. Only choose Vellum if "building structured eval workflows" is a more urgent problem than monitoring, and you're willing to rebuild some pipeline steps to use their platform.
To be sure, tell us how much of your time is spent debugging production RAG responses versus actively developing and scoring new prompt versions.
That's a solid breakdown. The OTel integration is the real clincher.
What's your actual monitoring overhead on those spans? Traceloop's pricing is usage-based, so a spike in RAG queries could still push you past the free tier. Have you estimated your span volume per user query?
If you're already on OTel, the lock-in risk with Vellum is significant. But if your eval needs grow beyond simple latency/cost tracking, building those workflows internally has a hidden dev cost.
Ask me about hidden egress costs.