From 3c2d109771e8fde68fd25e977dbfc3cc38bdee96 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Thu, 18 Sep 2025 15:24:54 +0800
Subject: [PATCH 1/9] Change default duration metrics unit from `ms` to `s`

---
 .chloggen/fix-42462.yaml                      | 30 +++++++++++++++++++
 connector/spanmetricsconnector/README.md      |  2 +-
 connector/spanmetricsconnector/config_test.go |  2 +-
 connector/spanmetricsconnector/connector.go   |  2 +-
 .../spanmetricsconnector/connector_test.go    | 14 ++++-----
 connector/spanmetricsconnector/factory.go     |  8 ++---
 .../spanmetricsconnector/factory_test.go      |  4 +++
 7 files changed, 48 insertions(+), 14 deletions(-)
 create mode 100644 .chloggen/fix-42462.yaml

diff --git a/.chloggen/fix-42462.yaml b/.chloggen/fix-42462.yaml
new file mode 100644
index 0000000000000..4cbc96a5ba30a
--- /dev/null
+++ b/.chloggen/fix-42462.yaml
@@ -0,0 +1,30 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: spanmetricsconnector
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Change default duration metrics unit from `ms` to `s`
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [42462]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  This change will result in a breaking change:
+  - There is no breaking change if the user has manually set the `unit` configuration.
+  - A breaking change will occur if the user relies on the default `unit` setting; in this case, please manually revert it to the desired `unit`.
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]
diff --git a/connector/spanmetricsconnector/README.md b/connector/spanmetricsconnector/README.md
index 32cb665db33dd..9fa20809ba393 100644
--- a/connector/spanmetricsconnector/README.md
+++ b/connector/spanmetricsconnector/README.md
@@ -96,7 +96,7 @@ The following settings can be optionally configured:
 - `histogram` (default: `explicit`): Use to configure the type of histogram to record
   calculated from spans duration measurements. Must be either `explicit` or `exponential`.
   - `disable` (default: `false`): Disable all histogram metrics.
-  - `unit` (default: `ms`): The time unit for recording duration measurements.
+  - `unit` (default: `s`): The time unit for recording duration measurements.
   calculated from spans duration measurements. One of either: `ms` or `s`.
   - `dimensions`: additional attributes to add as dimensions to the `traces.span.metrics.duration` metric, 
   which will be included _on top of_ the common and configured `dimensions` for span attributes and resource attributes.
diff --git a/connector/spanmetricsconnector/config_test.go b/connector/spanmetricsconnector/config_test.go
index e1e5ae164cbb6..557ca8ee4b0b1 100644
--- a/connector/spanmetricsconnector/config_test.go
+++ b/connector/spanmetricsconnector/config_test.go
@@ -87,7 +87,7 @@ func TestLoadConfig(t *testing.T) {
 					MaxPerDataPoint: defaultMaxPerDatapoint,
 				},
 				Histogram: HistogramConfig{
-					Unit: metrics.Milliseconds,
+					Unit: metrics.Seconds,
 					Exponential: configoptional.Some(ExponentialHistogramConfig{
 						MaxSize: 10,
 					}),
diff --git a/connector/spanmetricsconnector/connector.go b/connector/spanmetricsconnector/connector.go
index 26ecc414e2b68..0f6fa6ef564ab 100644
--- a/connector/spanmetricsconnector/connector.go
+++ b/connector/spanmetricsconnector/connector.go
@@ -43,7 +43,7 @@ const (
 	metricNameCalls    = "calls"
 	metricNameEvents   = "events"
 
-	defaultUnit = metrics.Milliseconds
+	defaultUnit = metrics.Seconds
 
 	// https://github.com/open-telemetry/opentelemetry-go/blob/3ae002c3caf3e44387f0554dfcbbde2c5aab7909/sdk/metric/internal/aggregate/limit.go#L11C36-L11C50
 	overflowKey = "otel.metric.overflow"
diff --git a/connector/spanmetricsconnector/connector_test.go b/connector/spanmetricsconnector/connector_test.go
index 325b50090fe94..9aff73a5bf698 100644
--- a/connector/spanmetricsconnector/connector_test.go
+++ b/connector/spanmetricsconnector/connector_test.go
@@ -50,7 +50,7 @@ const (
 	resourceMetricsCacheSize = 5
 
 	sampleRegion   = "us-east-1"
-	sampleDuration = float64(11)
+	sampleDuration = 11 * time.Millisecond
 
 	instanceID = "0044953a-2946-449f-a5c8-2971f2a63928"
 )
@@ -231,7 +231,7 @@ func verifyExplicitHistogramDataPoints(tb testing.TB, dps pmetric.HistogramDataP
 		dp := dps.At(dpi)
 		assert.Equal(
 			tb,
-			sampleDuration*float64(numCumulativeConsumptions),
+			sampleDuration.Seconds()*float64(numCumulativeConsumptions),
 			dp.Sum(),
 			"Should be a 11ms duration measurement, multiplied by the number of stateful accumulations.")
 		assert.NotZero(tb, dp.Timestamp(), "Timestamp should be set")
@@ -245,7 +245,7 @@ func verifyExplicitHistogramDataPoints(tb testing.TB, dps pmetric.HistogramDataP
 		// Find the bucket index where the 11ms duration should belong in.
 		var foundDurationIndex int
 		for foundDurationIndex = 0; foundDurationIndex < dp.ExplicitBounds().Len(); foundDurationIndex++ {
-			if dp.ExplicitBounds().At(foundDurationIndex) > sampleDuration {
+			if dp.ExplicitBounds().At(foundDurationIndex) > sampleDuration.Seconds() {
 				break
 			}
 		}
@@ -270,7 +270,7 @@ func verifyExponentialHistogramDataPoints(tb testing.TB, dps pmetric.Exponential
 		dp := dps.At(dpi)
 		assert.Equal(
 			tb,
-			sampleDuration*float64(numCumulativeConsumptions),
+			sampleDuration.Seconds()*float64(numCumulativeConsumptions),
 			dp.Sum(),
 			"Should be a 11ms duration measurement, multiplied by the number of stateful accumulations.")
 		assert.Equal(tb, uint64(numCumulativeConsumptions), dp.Count())
@@ -325,7 +325,7 @@ func buildBadSampleTrace() ptrace.Traces {
 	// Flipping timestamp for a bad duration
 	span.SetEndTimestamp(pcommon.NewTimestampFromTime(now))
 	span.SetStartTimestamp(
-		pcommon.NewTimestampFromTime(now.Add(time.Duration(sampleDuration) * time.Millisecond)))
+		pcommon.NewTimestampFromTime(now.Add(sampleDuration)))
 	return badTrace
 }
 
@@ -394,7 +394,7 @@ func initSpan(span span, s ptrace.Span) {
 	now := time.Now()
 	s.SetStartTimestamp(pcommon.NewTimestampFromTime(now))
 	s.SetEndTimestamp(
-		pcommon.NewTimestampFromTime(now.Add(time.Duration(sampleDuration) * time.Millisecond)))
+		pcommon.NewTimestampFromTime(now.Add(sampleDuration)))
 
 	s.Attributes().PutStr(stringAttrName, "stringAttrValue")
 	s.Attributes().PutInt(intAttrName, 99)
@@ -1371,7 +1371,7 @@ func TestConnector_durationsToUnits(t *testing.T) {
 				3 * time.Second,
 			},
 			unit: defaultUnit,
-			want: []float64{0.000003, 0.003, 3, 3000},
+			want: []float64{3e-09, 3e-06, 0.003, 3},
 		},
 		{
 			input: []time.Duration{
diff --git a/connector/spanmetricsconnector/factory.go b/connector/spanmetricsconnector/factory.go
index 6dea8ab1ef626..456e34586db9a 100644
--- a/connector/spanmetricsconnector/factory.go
+++ b/connector/spanmetricsconnector/factory.go
@@ -21,9 +21,9 @@ import (
 )
 
 const (
-	DefaultNamespace                 = "traces.span.metrics"
-	legacyMetricNamesFeatureGateID   = "connector.spanmetrics.legacyMetricNames"
-	includeCollectorInstanceIDGateID = "connector.spanmetrics.includeCollectorInstanceID"
+	DefaultNamespace                        = "traces.span.metrics"
+	legacyMetricNamesFeatureGateID          = "connector.spanmetrics.legacyMetricNames"
+	includeCollectorInstanceIDFeatureGateID = "connector.spanmetrics.includeCollectorInstanceID"
 )
 
 var (
@@ -40,7 +40,7 @@ func init() {
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/33227"),
 	)
 	includeCollectorInstanceID = featuregate.GlobalRegistry().MustRegister(
-		includeCollectorInstanceIDGateID,
+		includeCollectorInstanceIDFeatureGateID,
 		featuregate.StageAlpha,
 		featuregate.WithRegisterDescription("When enabled, connector add collector.instance.id to default dimensions."),
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/40400"),
diff --git a/connector/spanmetricsconnector/factory_test.go b/connector/spanmetricsconnector/factory_test.go
index 845e847a9347d..594921ffbf2ff 100644
--- a/connector/spanmetricsconnector/factory_test.go
+++ b/connector/spanmetricsconnector/factory_test.go
@@ -68,3 +68,7 @@ func TestNewConnector(t *testing.T) {
 		})
 	}
 }
+
+func TestCreateDefaultConfig(t *testing.T) {
+
+}

From 2b5bf68cd0f278f4d061dd3e467f8add98227037 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Fri, 19 Sep 2025 14:17:31 +0800
Subject: [PATCH 2/9] update

---
 .chloggen/fix-42462.yaml                      | 11 ++++++---
 connector/spanmetricsconnector/README.md      |  2 +-
 connector/spanmetricsconnector/config_test.go |  4 ++++
 connector/spanmetricsconnector/factory.go     | 23 +++++++++++++++----
 .../spanmetricsconnector/factory_test.go      |  4 ----
 5 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/.chloggen/fix-42462.yaml b/.chloggen/fix-42462.yaml
index 4cbc96a5ba30a..6c6397daf5a24 100644
--- a/.chloggen/fix-42462.yaml
+++ b/.chloggen/fix-42462.yaml
@@ -16,9 +16,14 @@ issues: [42462]
 # These lines will be padded with 2 spaces and then inserted directly into the document.
 # Use pipe (|) for multiline entries.
 subtext: |
-  This change will result in a breaking change:
-  - There is no breaking change if the user has manually set the `unit` configuration.
-  - A breaking change will occur if the user relies on the default `unit` setting; in this case, please manually revert it to the desired `unit`.
+  This change introduces a breaking change, which is now guarded by the feature gate `connector.spanmetrics.legacyDefaultMetricsUnit`.
+  Currently, the feature gate is enabled by default, so the unit will remain `ms`. After one or two release cycles, the unit will switch to `s` and the feature gate will also be disabled by default.
+  To revert this change manually, users can either enable the feature gate or modify the configuration as follows:
+  ```
+  spanmetrics:
+  histogram:
+    unit: "ms"
+  ```
 
 # If your change doesn't affect end users or the exported elements of any package,
 # you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
diff --git a/connector/spanmetricsconnector/README.md b/connector/spanmetricsconnector/README.md
index 9fa20809ba393..016a648b0c5c7 100644
--- a/connector/spanmetricsconnector/README.md
+++ b/connector/spanmetricsconnector/README.md
@@ -96,7 +96,7 @@ The following settings can be optionally configured:
 - `histogram` (default: `explicit`): Use to configure the type of histogram to record
   calculated from spans duration measurements. Must be either `explicit` or `exponential`.
   - `disable` (default: `false`): Disable all histogram metrics.
-  - `unit` (default: `s`): The time unit for recording duration measurements.
+  - `unit` (default: `ms`, it will change to `s` in the featurn release, you can enable feature-gate `connector.spanmetrics.legacyDefaultMetricsUnit` to keep use `ms` unit): The time unit for recording duration measurements.
   calculated from spans duration measurements. One of either: `ms` or `s`.
   - `dimensions`: additional attributes to add as dimensions to the `traces.span.metrics.duration` metric, 
   which will be included _on top of_ the common and configured `dimensions` for span attributes and resource attributes.
diff --git a/connector/spanmetricsconnector/config_test.go b/connector/spanmetricsconnector/config_test.go
index 557ca8ee4b0b1..6f20966ee0fc5 100644
--- a/connector/spanmetricsconnector/config_test.go
+++ b/connector/spanmetricsconnector/config_test.go
@@ -16,6 +16,7 @@ import (
 	"go.opentelemetry.io/collector/config/configoptional"
 	"go.opentelemetry.io/collector/confmap/confmaptest"
 	"go.opentelemetry.io/collector/confmap/xconfmap"
+	"go.opentelemetry.io/collector/featuregate"
 	"go.opentelemetry.io/collector/pdata/pmetric"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/connector/spanmetricsconnector/internal/metadata"
@@ -25,6 +26,9 @@ import (
 func TestLoadConfig(t *testing.T) {
 	t.Parallel()
 
+	// disable legacyDefaultMetricsUnit featuregate
+	require.NoError(t, featuregate.GlobalRegistry().Set(legacyDefaultMetricsUnit.ID(), false))
+
 	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "config.yaml"))
 	require.NoError(t, err)
 
diff --git a/connector/spanmetricsconnector/factory.go b/connector/spanmetricsconnector/factory.go
index 456e34586db9a..c68941bbd39db 100644
--- a/connector/spanmetricsconnector/factory.go
+++ b/connector/spanmetricsconnector/factory.go
@@ -18,17 +18,20 @@ import (
 	"go.opentelemetry.io/collector/pdata/pcommon"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/connector/spanmetricsconnector/internal/metadata"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/connector/spanmetricsconnector/internal/metrics"
 )
 
 const (
 	DefaultNamespace                        = "traces.span.metrics"
 	legacyMetricNamesFeatureGateID          = "connector.spanmetrics.legacyMetricNames"
 	includeCollectorInstanceIDFeatureGateID = "connector.spanmetrics.includeCollectorInstanceID"
+	legacyDefaultMetricsUnitFeatureGateID   = "connector.spanmetrics.legacyDefaultMetricsUnit"
 )
 
 var (
 	legacyMetricNamesFeatureGate *featuregate.Gate
 	includeCollectorInstanceID   *featuregate.Gate
+	legacyDefaultMetricsUnit     *featuregate.Gate
 )
 
 func init() {
@@ -45,6 +48,12 @@ func init() {
 		featuregate.WithRegisterDescription("When enabled, connector add collector.instance.id to default dimensions."),
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/40400"),
 	)
+	legacyDefaultMetricsUnit = featuregate.GlobalRegistry().MustRegister(
+		legacyDefaultMetricsUnitFeatureGateID,
+		featuregate.StageBeta, // current enabled by default and disable it in the feature release
+		featuregate.WithRegisterDescription("enabled by default, connector use ms unit for duration metrics."),
+		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/42103"),
+	)
 }
 
 // NewFactory creates a factory for the spanmetrics connector.
@@ -58,10 +67,16 @@ func NewFactory() connector.Factory {
 
 func createDefaultConfig() component.Config {
 	return &Config{
-		AggregationTemporality:      "AGGREGATION_TEMPORALITY_CUMULATIVE",
-		ResourceMetricsCacheSize:    defaultResourceMetricsCacheSize,
-		MetricsFlushInterval:        60 * time.Second,
-		Histogram:                   HistogramConfig{Disable: false, Unit: defaultUnit},
+		AggregationTemporality:   "AGGREGATION_TEMPORALITY_CUMULATIVE",
+		ResourceMetricsCacheSize: defaultResourceMetricsCacheSize,
+		MetricsFlushInterval:     60 * time.Second,
+		Histogram: HistogramConfig{Disable: false, Unit: func() metrics.Unit {
+			if legacyDefaultMetricsUnit.IsEnabled() {
+				return metrics.Milliseconds
+			}
+
+			return metrics.Seconds
+		}()},
 		Namespace:                   DefaultNamespace,
 		AggregationCardinalityLimit: 0,
 		Exemplars: ExemplarsConfig{
diff --git a/connector/spanmetricsconnector/factory_test.go b/connector/spanmetricsconnector/factory_test.go
index 594921ffbf2ff..845e847a9347d 100644
--- a/connector/spanmetricsconnector/factory_test.go
+++ b/connector/spanmetricsconnector/factory_test.go
@@ -68,7 +68,3 @@ func TestNewConnector(t *testing.T) {
 		})
 	}
 }
-
-func TestCreateDefaultConfig(t *testing.T) {
-
-}

From ae24de14931983144501d5b97e817a65e91b3157 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Mon, 22 Sep 2025 15:25:41 +0800
Subject: [PATCH 3/9] Update connector/spanmetricsconnector/README.md

Co-authored-by: Antoine Toulme <antoine@toulme.name>
---
 connector/spanmetricsconnector/README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/connector/spanmetricsconnector/README.md b/connector/spanmetricsconnector/README.md
index 016a648b0c5c7..9a71da501d702 100644
--- a/connector/spanmetricsconnector/README.md
+++ b/connector/spanmetricsconnector/README.md
@@ -96,7 +96,7 @@ The following settings can be optionally configured:
 - `histogram` (default: `explicit`): Use to configure the type of histogram to record
   calculated from spans duration measurements. Must be either `explicit` or `exponential`.
   - `disable` (default: `false`): Disable all histogram metrics.
-  - `unit` (default: `ms`, it will change to `s` in the featurn release, you can enable feature-gate `connector.spanmetrics.legacyDefaultMetricsUnit` to keep use `ms` unit): The time unit for recording duration measurements.
+  - `unit` (default: `ms`, it will change to `s` in the next release, you can enable feature-gate `connector.spanmetrics.legacyDefaultMetricsUnit` to keep use `ms` unit): The time unit for recording duration measurements.
   calculated from spans duration measurements. One of either: `ms` or `s`.
   - `dimensions`: additional attributes to add as dimensions to the `traces.span.metrics.duration` metric, 
   which will be included _on top of_ the common and configured `dimensions` for span attributes and resource attributes.

From eb7c81af97d54254710b2d5474c2a33af99bab24 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Mon, 22 Sep 2025 15:47:41 +0800
Subject: [PATCH 4/9] apply review's suggestion

---
 .chloggen/fix-42462.yaml                  | 7 ++++---
 connector/spanmetricsconnector/factory.go | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/.chloggen/fix-42462.yaml b/.chloggen/fix-42462.yaml
index 6c6397daf5a24..4efeacc712ac0 100644
--- a/.chloggen/fix-42462.yaml
+++ b/.chloggen/fix-42462.yaml
@@ -20,9 +20,10 @@ subtext: |
   Currently, the feature gate is enabled by default, so the unit will remain `ms`. After one or two release cycles, the unit will switch to `s` and the feature gate will also be disabled by default.
   To revert this change manually, users can either enable the feature gate or modify the configuration as follows:
   ```
-  spanmetrics:
-  histogram:
-    unit: "ms"
+  connectors
+    spanmetrics:
+      histogram:
+        unit: "ms"
   ```
 
 # If your change doesn't affect end users or the exported elements of any package,
diff --git a/connector/spanmetricsconnector/factory.go b/connector/spanmetricsconnector/factory.go
index c68941bbd39db..ae6ded7827611 100644
--- a/connector/spanmetricsconnector/factory.go
+++ b/connector/spanmetricsconnector/factory.go
@@ -50,7 +50,7 @@ func init() {
 	)
 	legacyDefaultMetricsUnit = featuregate.GlobalRegistry().MustRegister(
 		legacyDefaultMetricsUnitFeatureGateID,
-		featuregate.StageBeta, // current enabled by default and disable it in the feature release
+		featuregate.StageBeta, // current enabled by default and disable it in the next release
 		featuregate.WithRegisterDescription("enabled by default, connector use ms unit for duration metrics."),
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/42103"),
 	)

From 2b03261dcb23f1be43396bda2cfd59f8f25c0430 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Fri, 26 Sep 2025 11:17:33 +0800
Subject: [PATCH 5/9] use alpha stage feature-gate

---
 .chloggen/fix-42462.yaml                      |  4 ++--
 connector/spanmetricsconnector/README.md      | 14 +++++++++++++-
 connector/spanmetricsconnector/config_test.go |  4 +---
 connector/spanmetricsconnector/factory.go     | 18 +++++++++---------
 4 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/.chloggen/fix-42462.yaml b/.chloggen/fix-42462.yaml
index 4efeacc712ac0..f09671fb670e5 100644
--- a/.chloggen/fix-42462.yaml
+++ b/.chloggen/fix-42462.yaml
@@ -16,8 +16,8 @@ issues: [42462]
 # These lines will be padded with 2 spaces and then inserted directly into the document.
 # Use pipe (|) for multiline entries.
 subtext: |
-  This change introduces a breaking change, which is now guarded by the feature gate `connector.spanmetrics.legacyDefaultMetricsUnit`.
-  Currently, the feature gate is enabled by default, so the unit will remain `ms`. After one or two release cycles, the unit will switch to `s` and the feature gate will also be disabled by default.
+  This change introduces a breaking change, which is now guarded by the feature gate `connector.spanmetrics.useSCDefaultMetricsUnit`.
+  Currently, the feature gate is disabled by default, so the unit will remain `ms`. After one release cycle, the unit will switch to `s` and the feature gate will also be enabled by default.
   To revert this change manually, users can either enable the feature gate or modify the configuration as follows:
   ```
   connectors
diff --git a/connector/spanmetricsconnector/README.md b/connector/spanmetricsconnector/README.md
index 9a71da501d702..a216d1c26162f 100644
--- a/connector/spanmetricsconnector/README.md
+++ b/connector/spanmetricsconnector/README.md
@@ -23,6 +23,18 @@
 [Stability Level]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/component-stability.md#stability-levels
 <!-- end autogenerated section -->
 
+⚠️ Breaking Change Warning: 
+The default duration metrics unit will change from `ms` to `s` to adhere to the OpenTelemetry semantic conventions and a feature gate `connector.spanmetrics.useSCDefaultMetricsUnit` is also added.
+
+Currently, the feature gate is disabled by default, so the unit will remain `ms`. After one release cycle, the unit will switch to `s` and the feature gate will also be enabled by default.
+To revert this change manually, users can either disabled the feature gate or modify the configuration as follows:
+  ```
+  connectors
+    spanmetrics:
+      histogram:
+        unit: "ms"
+  ```
+
 ## Overview
 
 Aggregates Request, Error and Duration (R.E.D) OpenTelemetry metrics from span data.
@@ -96,7 +108,7 @@ The following settings can be optionally configured:
 - `histogram` (default: `explicit`): Use to configure the type of histogram to record
   calculated from spans duration measurements. Must be either `explicit` or `exponential`.
   - `disable` (default: `false`): Disable all histogram metrics.
-  - `unit` (default: `ms`, it will change to `s` in the next release, you can enable feature-gate `connector.spanmetrics.legacyDefaultMetricsUnit` to keep use `ms` unit): The time unit for recording duration measurements.
+  - `unit` (default: `ms`): The time unit for recording duration measurements.
   calculated from spans duration measurements. One of either: `ms` or `s`.
   - `dimensions`: additional attributes to add as dimensions to the `traces.span.metrics.duration` metric, 
   which will be included _on top of_ the common and configured `dimensions` for span attributes and resource attributes.
diff --git a/connector/spanmetricsconnector/config_test.go b/connector/spanmetricsconnector/config_test.go
index 6f20966ee0fc5..c971bf6b91f23 100644
--- a/connector/spanmetricsconnector/config_test.go
+++ b/connector/spanmetricsconnector/config_test.go
@@ -26,9 +26,7 @@ import (
 func TestLoadConfig(t *testing.T) {
 	t.Parallel()
 
-	// disable legacyDefaultMetricsUnit featuregate
-	require.NoError(t, featuregate.GlobalRegistry().Set(legacyDefaultMetricsUnit.ID(), false))
-
+	require.NoError(t, featuregate.GlobalRegistry().Set(useSCDefaultMetricsUnit.ID(), true))
 	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "config.yaml"))
 	require.NoError(t, err)
 
diff --git a/connector/spanmetricsconnector/factory.go b/connector/spanmetricsconnector/factory.go
index ae6ded7827611..896f852fcf064 100644
--- a/connector/spanmetricsconnector/factory.go
+++ b/connector/spanmetricsconnector/factory.go
@@ -25,13 +25,13 @@ const (
 	DefaultNamespace                        = "traces.span.metrics"
 	legacyMetricNamesFeatureGateID          = "connector.spanmetrics.legacyMetricNames"
 	includeCollectorInstanceIDFeatureGateID = "connector.spanmetrics.includeCollectorInstanceID"
-	legacyDefaultMetricsUnitFeatureGateID   = "connector.spanmetrics.legacyDefaultMetricsUnit"
+	useSCDefaultMetricsUnitFeatureGateID    = "connector.spanmetrics.useSCDefaultMetricsUnit"
 )
 
 var (
 	legacyMetricNamesFeatureGate *featuregate.Gate
 	includeCollectorInstanceID   *featuregate.Gate
-	legacyDefaultMetricsUnit     *featuregate.Gate
+	useSCDefaultMetricsUnit      *featuregate.Gate
 )
 
 func init() {
@@ -48,10 +48,10 @@ func init() {
 		featuregate.WithRegisterDescription("When enabled, connector add collector.instance.id to default dimensions."),
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/40400"),
 	)
-	legacyDefaultMetricsUnit = featuregate.GlobalRegistry().MustRegister(
-		legacyDefaultMetricsUnitFeatureGateID,
-		featuregate.StageBeta, // current enabled by default and disable it in the next release
-		featuregate.WithRegisterDescription("enabled by default, connector use ms unit for duration metrics."),
+	useSCDefaultMetricsUnit = featuregate.GlobalRegistry().MustRegister(
+		useSCDefaultMetricsUnitFeatureGateID,
+		featuregate.StageAlpha,
+		featuregate.WithRegisterDescription("When enabled, connector use second as default unit for duration metrics."),
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/42103"),
 	)
 }
@@ -71,11 +71,11 @@ func createDefaultConfig() component.Config {
 		ResourceMetricsCacheSize: defaultResourceMetricsCacheSize,
 		MetricsFlushInterval:     60 * time.Second,
 		Histogram: HistogramConfig{Disable: false, Unit: func() metrics.Unit {
-			if legacyDefaultMetricsUnit.IsEnabled() {
-				return metrics.Milliseconds
+			if useSCDefaultMetricsUnit.IsEnabled() {
+				return metrics.Seconds
 			}
 
-			return metrics.Seconds
+			return metrics.Milliseconds
 		}()},
 		Namespace:                   DefaultNamespace,
 		AggregationCardinalityLimit: 0,

From ab8d47067c2c8b4c566867b1224018ad20b23804 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Fri, 26 Sep 2025 22:08:59 +0800
Subject: [PATCH 6/9] Update .chloggen/fix-42462.yaml

Co-authored-by: Tyler Helmuth <12352919+TylerHelmuth@users.noreply.github.com>
---
 .chloggen/fix-42462.yaml | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/.chloggen/fix-42462.yaml b/.chloggen/fix-42462.yaml
index f09671fb670e5..bd90c458ab9b4 100644
--- a/.chloggen/fix-42462.yaml
+++ b/.chloggen/fix-42462.yaml
@@ -18,13 +18,6 @@ issues: [42462]
 subtext: |
   This change introduces a breaking change, which is now guarded by the feature gate `connector.spanmetrics.useSCDefaultMetricsUnit`.
   Currently, the feature gate is disabled by default, so the unit will remain `ms`. After one release cycle, the unit will switch to `s` and the feature gate will also be enabled by default.
-  To revert this change manually, users can either enable the feature gate or modify the configuration as follows:
-  ```
-  connectors
-    spanmetrics:
-      histogram:
-        unit: "ms"
-  ```
 
 # If your change doesn't affect end users or the exported elements of any package,
 # you should instead start your pull request title with [chore] or use the "Skip Changelog" label.

From 98b5a3beeb68a979aaa81a032e73f3a90a460389 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Fri, 26 Sep 2025 22:09:54 +0800
Subject: [PATCH 7/9] Update connector/spanmetricsconnector/README.md

Co-authored-by: Tyler Helmuth <12352919+TylerHelmuth@users.noreply.github.com>
---
 connector/spanmetricsconnector/README.md | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/connector/spanmetricsconnector/README.md b/connector/spanmetricsconnector/README.md
index a216d1c26162f..7f2a24685ba46 100644
--- a/connector/spanmetricsconnector/README.md
+++ b/connector/spanmetricsconnector/README.md
@@ -27,13 +27,6 @@
 The default duration metrics unit will change from `ms` to `s` to adhere to the OpenTelemetry semantic conventions and a feature gate `connector.spanmetrics.useSCDefaultMetricsUnit` is also added.
 
 Currently, the feature gate is disabled by default, so the unit will remain `ms`. After one release cycle, the unit will switch to `s` and the feature gate will also be enabled by default.
-To revert this change manually, users can either disabled the feature gate or modify the configuration as follows:
-  ```
-  connectors
-    spanmetrics:
-      histogram:
-        unit: "ms"
-  ```
 
 ## Overview
 

From 1577202b881fe14c1397c86c227ada793ad97bb6 Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Fri, 26 Sep 2025 22:13:51 +0800
Subject: [PATCH 8/9] update

---
 connector/spanmetricsconnector/config_test.go |  2 +-
 connector/spanmetricsconnector/factory.go     | 20 +++++++++----------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/connector/spanmetricsconnector/config_test.go b/connector/spanmetricsconnector/config_test.go
index c971bf6b91f23..75bc73f323ed6 100644
--- a/connector/spanmetricsconnector/config_test.go
+++ b/connector/spanmetricsconnector/config_test.go
@@ -26,7 +26,7 @@ import (
 func TestLoadConfig(t *testing.T) {
 	t.Parallel()
 
-	require.NoError(t, featuregate.GlobalRegistry().Set(useSCDefaultMetricsUnit.ID(), true))
+	require.NoError(t, featuregate.GlobalRegistry().Set(useSecondAsDefaultMetricsUnit.ID(), true))
 	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "config.yaml"))
 	require.NoError(t, err)
 
diff --git a/connector/spanmetricsconnector/factory.go b/connector/spanmetricsconnector/factory.go
index 896f852fcf064..f46d68d88e6de 100644
--- a/connector/spanmetricsconnector/factory.go
+++ b/connector/spanmetricsconnector/factory.go
@@ -22,16 +22,16 @@ import (
 )
 
 const (
-	DefaultNamespace                        = "traces.span.metrics"
-	legacyMetricNamesFeatureGateID          = "connector.spanmetrics.legacyMetricNames"
-	includeCollectorInstanceIDFeatureGateID = "connector.spanmetrics.includeCollectorInstanceID"
-	useSCDefaultMetricsUnitFeatureGateID    = "connector.spanmetrics.useSCDefaultMetricsUnit"
+	DefaultNamespace                           = "traces.span.metrics"
+	legacyMetricNamesFeatureGateID             = "connector.spanmetrics.legacyMetricNames"
+	includeCollectorInstanceIDFeatureGateID    = "connector.spanmetrics.includeCollectorInstanceID"
+	useSecondAsDefaultMetricsUnitFeatureGateID = "connector.spanmetrics.useSecondAsDefaultMetricsUnit"
 )
 
 var (
-	legacyMetricNamesFeatureGate *featuregate.Gate
-	includeCollectorInstanceID   *featuregate.Gate
-	useSCDefaultMetricsUnit      *featuregate.Gate
+	legacyMetricNamesFeatureGate  *featuregate.Gate
+	includeCollectorInstanceID    *featuregate.Gate
+	useSecondAsDefaultMetricsUnit *featuregate.Gate
 )
 
 func init() {
@@ -48,8 +48,8 @@ func init() {
 		featuregate.WithRegisterDescription("When enabled, connector add collector.instance.id to default dimensions."),
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/40400"),
 	)
-	useSCDefaultMetricsUnit = featuregate.GlobalRegistry().MustRegister(
-		useSCDefaultMetricsUnitFeatureGateID,
+	useSecondAsDefaultMetricsUnit = featuregate.GlobalRegistry().MustRegister(
+		useSecondAsDefaultMetricsUnitFeatureGateID,
 		featuregate.StageAlpha,
 		featuregate.WithRegisterDescription("When enabled, connector use second as default unit for duration metrics."),
 		featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/42103"),
@@ -71,7 +71,7 @@ func createDefaultConfig() component.Config {
 		ResourceMetricsCacheSize: defaultResourceMetricsCacheSize,
 		MetricsFlushInterval:     60 * time.Second,
 		Histogram: HistogramConfig{Disable: false, Unit: func() metrics.Unit {
-			if useSCDefaultMetricsUnit.IsEnabled() {
+			if useSecondAsDefaultMetricsUnit.IsEnabled() {
 				return metrics.Seconds
 			}
 

From cf1f2d18c0aa65a20beb92342ef39b6dc74414fe Mon Sep 17 00:00:00 2001
From: Murphy Chen <minquan.chen@daocloud.io>
Date: Sat, 27 Sep 2025 06:36:46 +0800
Subject: [PATCH 9/9] update

---
 .chloggen/fix-42462.yaml                 | 2 +-
 connector/spanmetricsconnector/README.md | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.chloggen/fix-42462.yaml b/.chloggen/fix-42462.yaml
index bd90c458ab9b4..395a9cd6d8bda 100644
--- a/.chloggen/fix-42462.yaml
+++ b/.chloggen/fix-42462.yaml
@@ -16,7 +16,7 @@ issues: [42462]
 # These lines will be padded with 2 spaces and then inserted directly into the document.
 # Use pipe (|) for multiline entries.
 subtext: |
-  This change introduces a breaking change, which is now guarded by the feature gate `connector.spanmetrics.useSCDefaultMetricsUnit`.
+  This change introduces a breaking change, which is now guarded by the feature gate `connector.spanmetrics.useSecondAsDefaultMetricsUnit`.
   Currently, the feature gate is disabled by default, so the unit will remain `ms`. After one release cycle, the unit will switch to `s` and the feature gate will also be enabled by default.
 
 # If your change doesn't affect end users or the exported elements of any package,
diff --git a/connector/spanmetricsconnector/README.md b/connector/spanmetricsconnector/README.md
index 7f2a24685ba46..2da51fcbf12e8 100644
--- a/connector/spanmetricsconnector/README.md
+++ b/connector/spanmetricsconnector/README.md
@@ -24,7 +24,7 @@
 <!-- end autogenerated section -->
 
 ⚠️ Breaking Change Warning: 
-The default duration metrics unit will change from `ms` to `s` to adhere to the OpenTelemetry semantic conventions and a feature gate `connector.spanmetrics.useSCDefaultMetricsUnit` is also added.
+The default duration metrics unit will change from `ms` to `s` to adhere to the OpenTelemetry semantic conventions and a feature gate `connector.spanmetrics.useSecondAsDefaultMetricsUnit` is also added.
 
 Currently, the feature gate is disabled by default, so the unit will remain `ms`. After one release cycle, the unit will switch to `s` and the feature gate will also be enabled by default.