Prometheus: Stabilize OpenTelemetry Exemplar to Prometheus Exemplar by dashpole · Pull Request #4964 · open-telemetry/opentelemetry-specification

dashpole · 2026-03-18T20:38:31Z

Changes

Editorial change: Move type-specific content to the respective type's section
Specify that the actual trace Id and span ID take precedence over keys with the name "trace_id" and "span_id", and that they should be dropped last.
Restructure spec into bullet points.

@open-telemetry/prometheus-interoperability @krajorama @ywwg @aknuds1

aknuds1

Generally LGTM, but I suggest renaming the Exemplars subsection on line 547 to Exemplar Conversion, for a unique and stable anchor.

Please also see my suggested change on line 466, and I'm wondering why there's no exemplar conversion mention in the ###Gauges section?

dashpole · 2026-04-06T17:14:57Z

I'm wondering why there's no exemplar conversion mention in the ###Gauges section?

Aren't these dropped?

aknuds1 · 2026-04-07T17:58:34Z

Aren't these dropped?

@dashpole Hm, I think it's right that Prometheus' OTLP endpoint drops exemplars for gauges, but I don't even know why. If dropping exemplars for gauges should be part of the spec, why not be explicit instead, and include the motivation?

aknuds1

Please see comment.

dashpole · 2026-04-07T18:28:52Z

Hm, I think it's right that Prometheus' OTLP endpoint drops exemplars for gauges, but I don't even know why. If dropping exemplars for gauges should be part of the spec, why not be explicit instead, and include the motivation?

Prometheus doesn't support exemplars on gauges or summaries. We could add that Exemplars SHOULD be dropped to each of them. We wouldn't want to say MUST because its possible Prometheus will support exemplars on those types in the future, and we would want to be able to support them if that happened.

…ervation

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

aknuds1 · 2026-04-08T06:47:45Z

Prometheus doesn't support exemplars on gauges or summaries. We could add that Exemplars SHOULD be dropped to each of them. We wouldn't want to say MUST because its possible Prometheus will support exemplars on those types in the future, and we would want to be able to support them if that happened.

@dashpole Yes, makes sense. Thanks!

dashpole · 2026-04-15T13:42:58Z

@aknuds1 can you take another review pass?

aknuds1 · 2026-04-16T10:55:49Z

Taking another look.

aknuds1

I think it looks pretty good, but please see suggestions.

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com> Co-authored-by: David Ashpole <dashpole@google.com>

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

### Context - Align environment variable context propagation name restrictions with POSIX.1-2024 and define normalization behavior. ([open-telemetry#4944](open-telemetry#4944)) - Decouple the responsibilities of the environment variable propagation carrier. ([open-telemetry#4961](open-telemetry#4961)) - Remove misleading implementation approach the environment variable propagation. ([open-telemetry#5003](open-telemetry#5003)) - Change Environment Variables as Context Propagation Carriers document status to Beta. ([open-telemetry#5020](open-telemetry#5020)) ### Traces - Stabilize Tracer `enabled` operation ([open-telemetry#4941](open-telemetry#4941)) - Stabilize `AlwaysRecord` sampler. ([open-telemetry#4934](open-telemetry#4934)) ### Metrics - Add development `maxExportBatchSize` parameter to Periodic exporting MetricReader. ([open-telemetry#4895](open-telemetry#4895)) ### Logs - Add event to span event bridge. ([open-telemetry#5006](open-telemetry#5006)) ### Resource - Clarify that a Resource describes the observed entity, not the component that technically emits telemetry. ([open-telemetry#4905](open-telemetry#4905)) ### Compatibility - Deprecate OpenTracing compatibility requirements in the specification. ([open-telemetry#4938](open-telemetry#4938)) - Stabilize sections of Prometheus and OpenMetrics Compatibility. - Stabilize Prometheus Classic Histogram to OTLP Explicit Histogram transformation. ([open-telemetry#4874](open-telemetry#4874)) - Stabilize Prometheus Timestamp and Start timestamp transformation. ([open-telemetry#4953](open-telemetry#4953)) - Clarify Prometheus Native Histogram to OTLP Exponential Histogram conversion, add conversion rules for Native Histograms with Custom Buckets (NHCB) to OTLP Histogram. ([open-telemetry#4898](open-telemetry#4898)) - Stabilize Prometheus Dropped Types transformation. ([open-telemetry#4952](open-telemetry#4952)) - Stabilize OpenTelemetry Attributes to Prometheus labels transformation. ([open-telemetry#4963](open-telemetry#4963)) - Stabilize Prometheus Exemplar to OpenTelemetry Exemplar transformation. ([open-telemetry#4962](open-telemetry#4962)) - Stabilize Prometheus Metadata transformation. ([open-telemetry#4954](open-telemetry#4954)) - Stabilize OpenTelemetry Metric Metadata to Prometheus metric metadata. ([open-telemetry#4966](open-telemetry#4966)) - Stabilize OpenTelemetry Exemplar to Prometheus Exemplar transformation. ([open-telemetry#4964](open-telemetry#4964)) - Stabilize sections of Prometheus Metrics Exporter. - Stabilize host configuration. ([open-telemetry#5025](open-telemetry#5025)) ### SDK Configuration - Declarative configuration: add in-development guidance for exposing the effective `Resource` returned by `Create`. ([open-telemetry#4949](open-telemetry#4949)) - Require spec changes to consider declarative config schema ([open-telemetry#4916](open-telemetry#4916)) - Add strict YAML parsing guidance to configuration supplementary guidelines. ([open-telemetry#4878](open-telemetry#4878)) ### OTEPs - Process Context: Sharing Resource Attributes with External Readers. ([open-telemetry#4719](open-telemetry#4719)) - Support multiple Resources within an SDK. ([open-telemetry#4665](open-telemetry#4665)) --------- Co-authored-by: Jack Berg <34418638+jack-berg@users.noreply.github.com>

@krajorama

…pen-telemetry#4964) Fixes open-telemetry#4925 ## Changes * Editorial change: Move type-specific content to the respective type's section * Specify that the actual trace Id and span ID take precedence over keys with the name "trace_id" and "span_id", and that they should be dropped last. * Restructure spec into bullet points. @open-telemetry/prometheus-interoperability @krajorama @ywwg @aknuds1 --------- Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

### Context - Align environment variable context propagation name restrictions with POSIX.1-2024 and define normalization behavior. ([open-telemetry#4944](open-telemetry#4944)) - Decouple the responsibilities of the environment variable propagation carrier. ([open-telemetry#4961](open-telemetry#4961)) - Remove misleading implementation approach the environment variable propagation. ([open-telemetry#5003](open-telemetry#5003)) - Change Environment Variables as Context Propagation Carriers document status to Beta. ([open-telemetry#5020](open-telemetry#5020)) ### Traces - Stabilize Tracer `enabled` operation ([open-telemetry#4941](open-telemetry#4941)) - Stabilize `AlwaysRecord` sampler. ([open-telemetry#4934](open-telemetry#4934)) ### Metrics - Add development `maxExportBatchSize` parameter to Periodic exporting MetricReader. ([open-telemetry#4895](open-telemetry#4895)) ### Logs - Add event to span event bridge. ([open-telemetry#5006](open-telemetry#5006)) ### Resource - Clarify that a Resource describes the observed entity, not the component that technically emits telemetry. ([open-telemetry#4905](open-telemetry#4905)) ### Compatibility - Deprecate OpenTracing compatibility requirements in the specification. ([open-telemetry#4938](open-telemetry#4938)) - Stabilize sections of Prometheus and OpenMetrics Compatibility. - Stabilize Prometheus Classic Histogram to OTLP Explicit Histogram transformation. ([open-telemetry#4874](open-telemetry#4874)) - Stabilize Prometheus Timestamp and Start timestamp transformation. ([open-telemetry#4953](open-telemetry#4953)) - Clarify Prometheus Native Histogram to OTLP Exponential Histogram conversion, add conversion rules for Native Histograms with Custom Buckets (NHCB) to OTLP Histogram. ([open-telemetry#4898](open-telemetry#4898)) - Stabilize Prometheus Dropped Types transformation. ([open-telemetry#4952](open-telemetry#4952)) - Stabilize OpenTelemetry Attributes to Prometheus labels transformation. ([open-telemetry#4963](open-telemetry#4963)) - Stabilize Prometheus Exemplar to OpenTelemetry Exemplar transformation. ([open-telemetry#4962](open-telemetry#4962)) - Stabilize Prometheus Metadata transformation. ([open-telemetry#4954](open-telemetry#4954)) - Stabilize OpenTelemetry Metric Metadata to Prometheus metric metadata. ([open-telemetry#4966](open-telemetry#4966)) - Stabilize OpenTelemetry Exemplar to Prometheus Exemplar transformation. ([open-telemetry#4964](open-telemetry#4964)) - Stabilize sections of Prometheus Metrics Exporter. - Stabilize host configuration. ([open-telemetry#5025](open-telemetry#5025)) ### SDK Configuration - Declarative configuration: add in-development guidance for exposing the effective `Resource` returned by `Create`. ([open-telemetry#4949](open-telemetry#4949)) - Require spec changes to consider declarative config schema ([open-telemetry#4916](open-telemetry#4916)) - Add strict YAML parsing guidance to configuration supplementary guidelines. ([open-telemetry#4878](open-telemetry#4878)) ### OTEPs - Process Context: Sharing Resource Attributes with External Readers. ([open-telemetry#4719](open-telemetry#4719)) - Support multiple Resources within an SDK. ([open-telemetry#4665](open-telemetry#4665)) --------- Co-authored-by: Jack Berg <34418638+jack-berg@users.noreply.github.com>

dashpole requested review from a team as code owners March 18, 2026 20:38

dashpole force-pushed the otel_to_prom_exemplar branch from 3b7c4e9 to 8722bb7 Compare March 18, 2026 20:38

dashpole added this to Prometheus SIG Mar 18, 2026

dashpole moved this to In progress in Prometheus SIG Mar 18, 2026

ArthurSens approved these changes Mar 30, 2026

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Prometheus: Stabililze OpenTelemetry Exemplar to Prometheus Exemplar

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omit exemplars from lower buckets, and remove language about key pres…

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Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

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Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

fix links

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dashpole force-pushed the otel_to_prom_exemplar branch from 2632731 to 75ffe03 Compare April 7, 2026 18:54

clarify when exemplars are dropped

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marcalff changed the title ~~Prometheus: Stabililze OpenTelemetry Exemplar to Prometheus Exemplar~~ Prometheus: Stabilize OpenTelemetry Exemplar to Prometheus Exemplar Apr 8, 2026

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Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com> Co-authored-by: David Ashpole <dashpole@google.com>

Merge branch 'main' into otel_to_prom_exemplar

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Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

dashpole added this pull request to the merge queue Apr 16, 2026

Merged via the queue into open-telemetry:main with commit b9b5fbb Apr 16, 2026
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dashpole deleted the otel_to_prom_exemplar branch April 16, 2026 15:05

github-project-automation Bot moved this from In progress to Done in Prometheus SIG Apr 16, 2026

carlosalberto mentioned this pull request Apr 20, 2026

Release 1.56 #5029

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dashpole commented Mar 18, 2026

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