Versioning and stability: Remove confusion around backwards compatiblity

CHANGELOG.md

@@ -51,6 +51,9 @@ release.
 
 ### Common
 
+- Versioning and stability: Clarify backwards compatibility and SemVer.
+  ([#4039](https://github.com/open-telemetry/opentelemetry-specification/pull/4039))
+
 ### Supplementary Guidelines
 
 ## v1.32.0 (2024-04-11)

specification/versioning-and-stability.md

@@ -126,7 +126,6 @@ maintainers SHOULD choose the idiomatic way for their language.
 
 #### SDK Stability
 
-Public portions of SDK packages MUST remain backwards compatible.
 There are two categories of public features: **plugin interfaces** and **constructors**.
 Examples of plugins include the SpanProcessor, Exporter, and Sampler interfaces.
 Examples of constructors include configuration objects, environment variables, and SDK builders.
@@ -144,8 +143,6 @@ in [Telemetry Stability](telemetry-stability.md).) The goal is to ensure users c
 update to the latest version of OpenTelemetry, and not be held back by the
 plugins that they depend on.
 
-Public portions of contrib packages (constructors, configuration, interfaces) SHOULD remain backwards compatible.
-
 Languages which ship binary artifacts SHOULD offer [ABI compatibility](glossary.md#abi-compatibility) for contrib packages.
 
 **Exception:** Contrib packages MAY break stability when a required downstream dependency breaks stability.
@@ -310,7 +307,7 @@ We invented a new tracing API, but continue to support the old one.
 
 ## Version numbers
 
-OpenTelemetry clients follow [Semantic Versioning 2.0.0](https://semver.org/spec/v2.0.0.html), with the following clarifications.
+OpenTelemetry clients MUST follow [Semantic Versioning 2.0.0](https://semver.org/spec/v2.0.0.html), with the following clarifications.
 
 OpenTelemetry clients have four components: API, SDK, Semantic Conventions, and Contrib.