Sourced from go.opentelemetry.io/otel's changelog.

[1.39.0/0.61.0/0.15.0/0.0.14] 2025-12-05

Added

• Greatly reduce the cost of recording metrics in go.opentelemetry.io/otel/sdk/metric using hashing for map keys. (#7175)
• Add WithInstrumentationAttributeSet option to go.opentelemetry.io/otel/log, go.opentelemetry.io/otel/metric, and go.opentelemetry.io/otel/trace packages. This provides a concurrent-safe and performant alternative to WithInstrumentationAttributes by accepting a pre-constructed attribute.Set. (#7287)
• Add experimental observability for the Prometheus exporter in go.opentelemetry.io/otel/exporters/prometheus. Check the go.opentelemetry.io/otel/exporters/prometheus/internal/x package documentation for more information. (#7345)
• Add experimental observability metrics in go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc. (#7353)
• Add temporality selector functions DeltaTemporalitySelector, CumulativeTemporalitySelector, LowMemoryTemporalitySelector to go.opentelemetry.io/otel/sdk/metric. (#7434)
• Add experimental observability metrics for simple log processor in go.opentelemetry.io/otel/sdk/log. (#7548)
• Add experimental observability metrics in go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc. (#7459)
• Add experimental observability metrics in go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp. (#7486)
• Add experimental observability metrics for simple span processor in go.opentelemetry.io/otel/sdk/trace. (#7374)
• Add experimental observability metrics in go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp. (#7512)
• Add experimental observability metrics for manual reader in go.opentelemetry.io/otel/sdk/metric. (#7524)
• Add experimental observability metrics for periodic reader in go.opentelemetry.io/otel/sdk/metric. (#7571)
• Support OTEL_EXPORTER_OTLP_LOGS_INSECURE and OTEL_EXPORTER_OTLP_INSECURE environmental variables in go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp. (#7608)
• Add Enabled method to the Processor interface in go.opentelemetry.io/otel/sdk/log. All Processor implementations now include an Enabled method. (#7639)
• The go.opentelemetry.io/otel/semconv/v1.38.0 package. The package contains semantic conventions from the v1.38.0 version of the OpenTelemetry Semantic Conventions. See the migration documentation for information on how to upgrade from go.opentelemetry.io/otel/semconv/v1.37.0.(#7648)

Changed

• Distinct in go.opentelemetry.io/otel/attribute is no longer guaranteed to uniquely identify an attribute set. Collisions between Distinct values for different Sets are possible with extremely high cardinality (billions of series per instrument), but are highly unlikely. (#7175)
• WithInstrumentationAttributes in go.opentelemetry.io/otel/trace synchronously de-duplicates the passed attributes instead of delegating it to the returned TracerOption. (#7266)
• WithInstrumentationAttributes in go.opentelemetry.io/otel/meter synchronously de-duplicates the passed attributes instead of delegating it to the returned MeterOption. (#7266)
• WithInstrumentationAttributes in go.opentelemetry.io/otel/log synchronously de-duplicates the passed attributes instead of delegating it to the returned LoggerOption. (#7266)
• Rename the OTEL_GO_X_SELF_OBSERVABILITY environment variable to OTEL_GO_X_OBSERVABILITY in go.opentelemetry.io/otel/sdk/trace, go.opentelemetry.io/otel/sdk/log, and go.opentelemetry.io/otel/exporters/stdout/stdouttrace. (#7302)
• Improve performance of histogram Record in go.opentelemetry.io/otel/sdk/metric when min and max are disabled using NoMinMax. (#7306)
• Improve error handling for dropped data during translation by using prometheus.NewInvalidMetric in go.opentelemetry.io/otel/exporters/prometheus. ⚠️ Breaking Change: Previously, these cases were only logged and scrapes succeeded. Now, when translation would drop data (e.g., invalid label/value), the exporter emits a NewInvalidMetric, and Prometheus scrapes fail with HTTP 500 by default. To preserve the prior behavior (scrapes succeed while errors are logged), configure your Prometheus HTTP handler with: promhttp.HandlerOpts{ ErrorHandling: promhttp.ContinueOnError }. (#7363)
• Replace fnv hash with xxhash in go.opentelemetry.io/otel/attribute for better performance. (#7371)
• The default TranslationStrategy in go.opentelemetry.io/exporters/prometheus is changed from otlptranslator.NoUTF8EscapingWithSuffixes to otlptranslator.UnderscoreEscapingWithSuffixes. (#7421)
• Improve performance of concurrent measurements in go.opentelemetry.io/otel/sdk/metric. (#7427)
• Include W3C TraceFlags (bits 0–7) in the OTLP Span.Flags field in go.opentelemetry.io/exporters/otlp/otlptrace/otlptracehttp and go.opentelemetry.io/exporters/otlp/otlptrace/otlptracegrpc. (#7438)
• The ErrorType function in go.opentelemetry.io/otel/semconv/v1.37.0 now handles custom error types. If an error implements an ErrorType() string method, the return value of that method will be used as the error type. (#7442)

Fixed

• Fix WithInstrumentationAttributes options in go.opentelemetry.io/otel/trace, go.opentelemetry.io/otel/metric, and go.opentelemetry.io/otel/log to properly merge attributes when passed multiple times instead of replacing them. Attributes with duplicate keys will use the last value passed. (#7300)
• The equality of attribute.Set when using the Equal method is not affected by the user overriding the empty set pointed to by attribute.EmptySet in go.opentelemetry.io/otel/attribute. (#7357)

... (truncated)

• 6ce1429 Release v1.39.0 (#7676)
• 12e421a sdk/log: move Enabled method from FilterProcessor to Processor (#7639)
• 5982f16 fix(deps): update module golang.org/x/sys to v0.39.0 (#7684)
• 9288378 chore(deps): update module golang.org/x/sync to v0.19.0 (#7683)
• ee3dfef chore(deps): update github.com/securego/gosec/v2 digest to 41f28e2 (#7682)
• 9345d1f fix(deps): update module github.com/golangci/golangci-lint/v2 to v2.7.2 (#7680)
• d03b033 Check context prior to delaying retry in OTLP exporters (#7678)
• 61765e7 Fix flaky TestClientInstrumentation (#7677)
• a54721c chore(deps): update module github.com/go-git/go-billy/v5 to v5.7.0 (#7679)
• 746d086 chore(deps): update github/codeql-action action to v4.31.7 (#7675)
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