Comparison
Nexus vs Braintrust
Braintrust is a powerful LLM evaluation platform — built for running experiments, comparing prompts, and tracking model performance over time. Here is an honest look at when Nexus makes more sense, and when Braintrust is the right choice.
TL;DR
Choose Nexus if you...
- ✓ Want production observability into multi-step agent workflows
- ✓ Need trace/span waterfalls showing exactly what your agent did
- ✓ Are an indie dev or small team watching spend closely
- ✓ Do not need a structured evaluation framework or test datasets
- ✓ Want $9/mo flat rate with no per-log usage fees
Choose Braintrust if you...
- ✓ Run structured LLM evals — compare prompts, models, configurations
- ✓ Need a dataset management and versioning system
- ✓ Want experiment tracking with statistical comparison
- ✓ Need a prompt playground to iterate on system prompts
- ✓ Have a team that prioritizes eval-driven development
The fundamental difference: observability vs evaluation
Nexus is observability-first: you instrument your agent code with the Nexus SDK and watch what happens in production — traces (full agent runs), spans (individual steps), latency, errors. The question Nexus answers is what did my agent do on this run?
Braintrust is eval-first: you define test datasets and scoring functions, then run experiments to compare different prompts, models, or code versions against those datasets. The question Braintrust answers is which version of my agent performs better?
These tools solve adjacent but different problems. Nexus is the right fit when you need to debug and monitor production agent runs. Braintrust is the right fit when you need to systematically evaluate and improve LLM quality before or after deploying. Many teams use both — Braintrust offline for evals, Nexus online for monitoring.
Pricing
| Plan | Nexus | Braintrust |
|---|---|---|
| Free | $0 · 1K traces/mo · 1 agent | $0 · 1K logs/mo |
| Pro / Team | $9/mo flat · 50K traces · unlimited agents | Usage-based · ~$1-3 per 1K logs above free tier |
| Enterprise | — | Custom pricing |
Braintrust pricing as of 2026 — usage-based costs vary by log volume. Nexus is flat-rate: $9/mo regardless of how many traces you send (up to 50K).
Feature comparison
| Feature | Nexus | Braintrust |
|---|---|---|
| Agent trace & span waterfall | ✓ | Partial |
| Production LLM logging | ✓ | ✓ |
| LLM evaluation framework | — | ✓ |
| Dataset management | — | ✓ |
| Experiment tracking | — | ✓ |
| Prompt playground | — | ✓ |
| Statistical eval comparison | — | ✓ |
| TypeScript SDK | ✓ open-source | ✓ |
| Python SDK | ✓ open-source | ✓ |
| Multi-agent dashboard | ✓ | Partial |
| Flat-rate pricing | ✓ $9/mo | — |
| Cloudflare edge (global CDN) | ✓ | — |
| Setup time | < 2 min | ~10-30 min (eval setup) |
| Self-hosted option | — | — |
The honest take
Braintrust is genuinely excellent for LLM evaluation. If your team is doing systematic prompt engineering — running the same prompt against 100 test cases, comparing GPT-4o vs Claude 3.5, scoring outputs with custom evaluators — Braintrust's eval framework and dataset management are best-in-class. It is built for teams that treat LLM quality as an engineering problem.
The tradeoff: Braintrust solves a different problem than observability. Knowing that prompt version B scores 12% better on your eval dataset does not tell you why a specific production agent run failed at step 3. For production debugging, you want real traces showing exactly which tool calls were made, what the LLM returned, and where latency spiked.
Nexus is built for the "what just happened?" question. When a user reports that your agent gave a wrong answer, you open the trace, see the full span waterfall, and immediately understand the sequence of events. No test dataset needed — you are debugging a real run.
The pricing structure is also meaningfully different: Braintrust's usage-based model makes sense for teams running many experiments, but costs can grow unexpectedly with log volume. At $9/mo flat, Nexus is more predictable for indie developers who want observability without a surprise invoice.
Related
- All AI agent monitoring alternatives — compare every tool side by side
- LlamaIndex observability guide — instrument RAG pipelines with Nexus
- Nexus pricing — free plan or $9/mo Pro
Try Nexus free — no credit card needed
1,000 traces/month free. Drop in 3 lines of code and see your first trace in under a minute.