### Breaking changes
* Global tags are now assigned early. This means that users have to make sure to not overwrite `meta`, but only add to it instead, if they don't want to lose global tags. Wrong: `$span->meta = [ 'some' => 'tag' ]`. Correct `$span->meta['some'] = 'tag'`.
* Support for legacy param `DD_TRACE_RESOURCE_URI_MAPPING` has been dropped with the migration to C code, after more than a year of deprecation. Use `DD_TRACE_RESOURCE_URI_FRAGMENT_REGEX`, `DD_TRACE_RESOURCE_URI_MAPPING_INCOMING`, and `DD_TRACE_RESOURCE_URI_MAPPING_OUTGOING ` instead. See [resource mapping](https://docs.datadoghq.com/tracing/setup_overview/setup/php/?tab=containers#map-resource-names-to-normalized-uri) for more details.
- (PHP 8) Migrate _dd.origin and distributed header sending to internal (#1267)
- (PHP 5) Add headers ZAI implementation (#1308)
- Add support for PHP 8.1 (#1297)