Transition plan where both old and new attributes are sent for a while

CHANGELOG.md

@@ -43,6 +43,9 @@ release.
   ([#3390](https://github.com/open-telemetry/opentelemetry-specification/pull/3390))
 - BREAKING: Remove `messaging.consumer.id`, make `messaging.client_id` generic
   ([#3336](https://github.com/open-telemetry/opentelemetry-specification/pull/3336))
+- Add transition plan for upcoming breaking changes to the unstable HTTP semantic
+  conventions.
+  ([#3443](https://github.com/open-telemetry/opentelemetry-specification/pull/3443))
 
 ### Compatibility
 

specification/metrics/semantic_conventions/http-metrics.md

@@ -26,6 +26,20 @@ operations. By adding HTTP attributes to metric events it allows for finely tune
 
 <!-- tocstop -->
 
+> **Warning**
+> HTTP instrumentation updating from
+> [v1.20.0 of this document](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/metrics/semantic_conventions/http-metrics.md)
+> (or prior) to the latest version SHOULD:
+>
+> * start emitting the latest semantic convention attributes on HTTP metrics
+>   _in addition_ to the attributes they are already emitting,
+>   without bumping the major version.
+>   (note: this SHOULD NOT increase cardinality or create new timeseries)
+> * maintain (security patching at a minimum) the existing major version
+>   for at least six months after it starts emitting both sets of attributes.
+> * stop emitting both sets of attributes in the next major version (stable
+>   next major version SHOULD NOT be released prior to October 1, 2023).
+
 ## HTTP Server
 
 ### Metric: `http.server.duration`

specification/trace/semantic_conventions/http.md

@@ -27,6 +27,19 @@ and various HTTP versions like 1.1, 2 and SPDY.
 
 <!-- tocstop -->
 
+> **Warning**
+> HTTP instrumentation updating from
+> [v1.20.0 of this document](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/trace/semantic_conventions/http.md)
+> (or prior) to the latest version SHOULD:
+>
+> * start emitting the latest semantic convention attributes on spans
+>   _in addition_ to the attributes they are already emitting,
+>   without bumping the major version.
+> * maintain (security patching at a minimum) the existing major version
+>   for at least six months after it starts emitting both sets of attributes.
+> * stop emitting both sets of attributes in the next major version (stable
+>   next major version SHOULD NOT be released prior to October 1, 2023).
+
 ## Name
 
 HTTP spans MUST follow the overall [guidelines for span names](../api.md#span).