### Added

- Add `ByteSlice` and `ByteSliceValue` functions for new `BYTESLICE`
attribute type in `go.opentelemetry.io/otel/attribute`. (#7948)
- Apply attribute value limit to the `KindBytes` attribute type in
`go.opentelemetry.io/otel/sdk/log`. (#7990)
- Apply attribute value limit to the `BYTESLICE` attribute type in
`go.opentelemetry.io/otel/sdk/trace`. (#7990)
- Support `BYTESLICE` attributes in `go.opentelemetry.io/otel/trace`.
(#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace`. (#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlplog`. (#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric`. (#8153)
- Support `BYTESLICE` attributes in
`go.opentelemetry.io/otel/exporters/zipkin`. (#8153)
- Add `String` method for `Value` type in
`go.opentelemetry.io/otel/attribute`. (#8142)
- Add `Slice` and `SliceValue` functions for new `SLICE` attribute type
in `go.opentelemetry.io/otel/attribute`. (#8166)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace`. (#8216)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlplog`. (#8216)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric`. (#8216)
- Support `SLICE` attributes in
`go.opentelemetry.io/otel/exporters/zipkin`. (#8216)
- Apply `AttributeValueLengthLimit` to `attribute.SLICE` type attribute
values in `go.opentelemetry.io/otel/sdk/trace`, recursively truncating
contained string values. (#8217)
- Add `Error` field on `Record` type in
`go.opentelemetry.io/otel/log/logtest`. (#8148)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
(#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc`. (#8157)
- Add `WithMaxRequestSize` option in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8157)
- Add `Settable` to `go.opentelemetry.io/otel/metric/x` to allow reusing
attribute options. (#8178)
- Add experimental support for splitting metric data across multiple
batches in `go.opentelemetry.io/otel/sdk/metric`.
Set `OTEL_GO_X_METRIC_EXPORT_BATCH_SIZE=<max_size>` to enable for all
periodic readers.
See `go.opentelemetry.io/otel/sdk/metric/internal/x` for feature
documentation. (#8071)
- Add experimental self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`.
  Enable with `OTEL_GO_X_SELF_OBSERVABILITY=true` environment variable.
See
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc/internal/x`
for feature documentation. (#8192)
- Add experimental self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
  Enable with `OTEL_GO_X_SELF_OBSERVABILITY=true` environment variable.
See
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp/internal/x`
for feature documentation. (#8194)
- Add experimental self-observability metrics in
`go.opentelemetry.io/otel/exporters/stdout/stdoutlog`.
  Enable with `OTEL_GO_X_SELF_OBSERVABILITY=true` environment variable.
See `go.opentelemetry.io/otel/stdout/stdoutlog/internal/x` for feature
documentation. (#8263)
- Add `WithDefaultAttributes` to `go.opentelemetry.io/otel/metric/x` to
support setting default attributes on instruments. (#8135)
- Add `go.opentelemetry.io/otel/semconv/v1.41.0` package.
The package contains semantic conventions from the `v1.41.0` version of
the OpenTelemetry Semantic Conventions.
See the [migration documentation](./semconv/v1.41.0/MIGRATION.md) for
information on how to upgrade from
`go.opentelemetry.io/otel/semconv/v1.40.0`. (#8324)
- Add Observable variants of instruments to
`go.opentelemetry.io/otel/semconv/v1.41.0` package. (#8350)
- Generate explicit histogram bucket boundaries from weaver
configuration for HTTP and RPC duration instruments in
`go.opentelemetry.io/otel/semconv/v1.41.0`. (#8002)

### Changed

- ⚠️ **Breaking Change:** `go.opentelemetry.io/otel/sdk/metric` now
applies a default cardinality limit of 2000 to comply with the Metrics
SDK specification recommendation.
New attribute sets are dropped when the cardinality limit is reached.
The measurement of these sets are aggregated into a special attribute
set containing `attribute.Bool("otel.metric.overflow", true)`.
  This can break users who relied on the previous unlimited default.
Set `WithCardinalityLimit(0)` or the deprecated
`OTEL_GO_X_CARDINALITY_LIMIT=0` environment variable to preserve
unlimited cardinality.
Note that support for `OTEL_GO_X_CARDINALITY_LIMIT` may be removed in a
future release. (#8247)
- `ErrorType` in `go.opentelemetry.io/otel/semconv` now unwraps errors
created with `fmt.Errorf` when deriving the `error.type` attribute.
(#8133)
- `go.opentelemetry.io/otel/sdk/log` now unwraps error chains created
with `fmt.Errorf` when deriving the `error.type` attribute from errors
on log records. (#8133)
- `Set.MarshalLog` method in `go.opentelemetry.io/otel/attribute` now
uses `Value.String` formatting following the [OpenTelemetry AnyValue
representation for non-OTLP
protocols](https://opentelemetry.io/docs/specs/otel/common/#anyvalue).
(#8169)
- Optimize `go.opentelemetry.io/otel/sdk/metric` to return a drop
reservoir and short-circuit `Offer` calls to the exemplar reservoir when
`exemplar.AlwaysOffFilter` is configured. (#8211) (#8267)
- Optimize `go.opentelemetry.io/otel/sdk/metric` to return a drop
reservoir for asynchronous instruments when `exemplar.TraceBasedFilter`
is configured. (#8286)

### Deprecated

- Deprecate `Value.Emit` method in `go.opentelemetry.io/otel/attribute`.
  Use `Value.String` instead. (#8176)

### Fixed

- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Limit OTLP request size to 64 MiB by default in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`.
The limit applies before compression, oversized requests are treated as
non-retryable errors, and the limit can be configured with the new
`WithMaxRequestSize` option. (#8157, #8365)
- Fix gzipped request body replay on redirect in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
(#8135)
- Fix gzipped request body replay on redirect in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8152)
- `go.opentelemetry.io/otel/exporters/prometheus` now uses
`Value.String` formatting for label values following the [OpenTelemetry
AnyValue representation for non-OTLP
protocols](https://opentelemetry.io/docs/specs/otel/common/#anyvalue).
(#8170)
- Propagate errors from the exporter when calling `Shutdown` on
`BatchSpanProcessor` in `go.opentelemetry.io/otel/sdk/trace`. (#8197)
- Fix stale status code reporting on self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp` and
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8226)
- Fix a concurrent `Collect` data race and potential panic in
`go.opentelemetry.io/otel/exporters/prometheus` when
`WithResourceAsConstantLabels` option is used. (#8227)
- Fix race condition in `FixedSizeReservoir` in
`go.opentelemetry.io/otel/sdk/metric/exemplar` by reverting #7447.
(#8249)
- Fix `FixedSizeReservoir` in
`go.opentelemetry.io/otel/sdk/metric/exemplar` to safely handle zero
size.
A capacity check in the constructor initializes the reservoir safely and
skips initialization for zero-cap; early returns in `Offer()` and
`Collect()` ensure no-op behavior. (#8295)
- Fix counting of spans and logs in self-observability metrics in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`,
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`,
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc`, and
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8254)
- Drop conflicting scope attributes named `name`, `version`, or
`schema_url` from metric labels in
`go.opentelemetry.io/otel/exporters/prometheus`, preserving the
dedicated `otel_scope_name`, `otel_scope_version`, and
`otel_scope_schema_url` labels. (#8264)
- Close schema files opened by `ParseFile` in
`go.opentelemetry.io/otel/schema/v1.0` and
`go.opentelemetry.io/otel/schema/v1.1`.
([GHSA-995v-fvrw-c78m](GHSA-995v-fvrw-c78m))
- Enforce the 8192-byte baggage size limit during extraction/parsing,
changing behavior when the limit is exceeded in
`go.opentelemetry.io/otel/baggage` and
`go.opentelemetry.io/otel/propagation`. (#8222)
- Fix `go.opentelemetry.io/otel/semconv/v1.41.0` to include `Attr*`
helper methods for required attributes on observable instruments.
(#8361)
- Limit baggage extraction error reporting in
`go.opentelemetry.io/otel/propagation` to prevent malformed or oversized
baggage headers from flooding logs.
([GHSA-5wrp-cwcj-q835](GHSA-5wrp-cwcj-q835))