What changed

• The repository now replaces the upstream Prometheus module with a Grafana-maintained fork containing a targeted fix for the remote write metric sent_batch_duration_seconds to start timing after the HTTP request is actually sent (rather than from before it was sent).
• Replace directive:
  • replace github.com/prometheus/prometheus => github.com/grafana/prometheus v1.8.2-0.20260302171028-8cf60eef5463
• Context:
  • Fork branch: https://github.com/grafana/prometheus/tree/fix-sent-batch-duration-v0.309.1
  • Upstream PR: remote write: fix sent_batch_duration_seconds measuring before the request is sent prometheus/prometheus#18214

Impact assessment

• API stability: No public API or config schema changes to Prometheus packages that are commonly imported by the OpenTelemetry Collector or its Prometheus receiver were introduced by this fork patch. It is a scoped behavioral fix to how an internal metric is timed during remote write.
• Compatibility: The fork is based on upstream v0.309.1 with the single backported fix. No intermediate upstream breaking changes are included.
• Runtime/metrics effect: The observed values of sent_batch_duration_seconds may decrease slightly because the timer starts closer to the actual send operation. This affects metric semantics only; not compilation or runtime behavior of the code depending on Prometheus libraries.

Code changes required in this repository

• None. The change is internal to the Prometheus remote write timing and does not require call-site or import changes.
• If you maintain dashboards/alerts that rely on sent_batch_duration_seconds, consider validating thresholds due to the corrected timing window. This is not a code change.

Evidence

• Upstream PR description (intent of change): “Fix sent_batch_duration_seconds measuring before the request was sent.” (PR #18214)
• Grafana fork branch name indicates it is a backport on v0.309.1: fix-sent-batch-duration-v0.309.1.

Relevant code snippet (illustrative of the fix; based on the PR description)

• The fix moves the timer start to immediately before the HTTP send:

  - start := time.Now()
    req, err := http.NewRequest("POST", url, body)
    if err != nil {
        // ...
    }
  + start := time.Now()
    resp, err := client.Do(req)
    // ...
    sentBatchDurationSeconds.Observe(time.Since(start).Seconds())

Notes on versioning/replace

• Although the fork is tagged v1.8.2-..., the replace maps github.com/prometheus/prometheus to github.com/grafana/prometheus, so no import path or module major-version changes are required in this repository.