As per the following change in the specification (1.14 releasing Oct 4):

OpenTelemetry protocol exporters SHOULD emit a User-Agent header to at a minimum identify the exporter, the language of its implementation, and the version of the exporter. For example, the Python OTLP exporter version 1.2.3 would report the following:
OTel OTLP Exporter Python/1.2.3

See https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md#user-agent