Full list of differences found in [this compare.](https://github.com/open-telemetry/opentelemetry-proto/compare/v0.3.0...v0.4.0)
Changed
* Metrics - Add temporality to MetricDescriptor (140).
Added
* Metrics - Add Monotonic Types (145)
* Common/Traces - Added support for arrays and maps for attribute values (AnyValue) (157).
Removed
* :stop_sign: [BREAKING] Metrics - Removed common labels from MetricDescriptor (144).
Errata
The following was announced in the release, but this was not considered Stable until `v0.5.0`
> This is a Release Candidate to declare Traces part of the protocol Stable.