• #1935 - remove CHANGES.md (@sungam3r)
• #1936, #1922 - README.md updates (@nblumhardt)
• #1942 - remove redundant GetTypeInfo() calls (@SimonCropp)
• #1947 - message template caching performance improvements (@epeshk)
• #1948 - reduce allocations in Logger.Write() (@epeshk)
• #1955 breaking - collect and propagate Activity.Current.TraceId and SpanId automatically in Logger.Write() (@nblumhardt)
• #1964 - don't cache reusable string writers with large buffer sizes (@Jakimar)
• #1969 - README.md updates (@bartelink)
• #1971 - drop test coverage for unsupported .NET Core versions (@bartelink)

Built-in trace and span id support

This release adds two new first-class properties to LogEvent: TraceId and SpanId. These are set automatically in Logger.Write() to the corresponding property values from System.Diagnostics.Activity.Current.

The major benefit of this change is that sinks, once updated, can reliably propagate trace and span ids through to back-ends that support them (in much the same way that first-class timestamps, messages, levels, and exceptions are used today).

The sinks maintained under serilog/serilog, along with formatting helpers such as Serilog.Formatting.Compact and Serilog.Expressions, are already compatible with this change or have pending releases that add compatibility.

Breaking change

Trace and span id collection includes support for {TraceId} and {SpanId} placeholders in output templates (commonly used when formatting text log files). Where previously these names resolved to user-defined properties, they now resolve to the built-in LogEvent.TraceId and LogEvent.SpanId values, respectively.

Impact is expected to be low, because the trace and span id values in any user-added properties are likely to be identical to the built-in ones.