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Observability for LLM Systems

6 min read

You'll learn to

  • -Understand what to log and trace in an LLM pipeline
  • -Design dashboards for latency, cost, and quality
  • -Implement real statistical anomaly detection on a metric time series

Clients deploy an AI feature and have zero visibility into its quality, cost, or performance. When something breaks, it takes days to even figure out what happened, let alone why. This is the same problem traditional software observability solved years ago, applied to a system with signals traditional observability was never built to track.

Four Signals, Not the Usual Three

Traditional observability tracks latency, throughput, and error rate. LLM systems need a fourth signal traditional tooling has no concept of: quality. A request that returns in 200ms with a 200 status code and a completely wrong or hallucinated answer looks perfectly healthy to every traditional monitoring tool, and that gap is exactly why AI-specific observability is its own discipline now, not just an extension of what already existed.

The Four Signals
The full request lifecycle: every retrieval, tool call, and generation step, end to end
Traces
Latency, throughput, and error rate, aggregated over time
Metrics
LLM-as-judge scoring on a sample of real traffic, the signal traditional tools cannot see
Quality
Token usage and dollar spend, traceable back to the specific request that caused it
Cost

Detecting an Anomaly Statistically, Not by Eyeballing a Chart

A dashboard nobody is actively watching catches nothing. Real alerting compares a live reading against the recent statistical baseline and fires when something is a genuine outlier, not merely a routine fluctuation.

Real z-score anomaly detection against a latency baseline

A z-score past roughly 3 means a reading is more than three standard deviations from the recent baseline, genuinely unusual rather than everyday noise. The same technique applies to cost per request and quality score just as directly as latency: track a rolling baseline, flag anything that departs from it by an unusual amount, alert on the flag rather than on a fixed hardcoded number that will not fit every system anyway.

Keep the Overhead Minimal

Tracing every request end to end sounds expensive, and done naively it would be. In practice, tracing runs asynchronously, off the critical path of the actual response, and quality evaluation samples only 10 to 20% of traffic rather than scoring every single request with an expensive judge call. The overhead this adds to the actual response the user is waiting on should stay under about 5 milliseconds, observability that costs the user noticeable latency defeats its own purpose.

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