Const ExperimentalSpans are counted as inflight from when they are passed to the exporter until the export operation has concluded. If the exporter retries failed export attempts, spans remain inflight across all retry attempts and any backoff between them.
This metric is experimental and is subject to breaking changes in minor releases of @opentelemetry/semantic-conventions.
The number of spans which were passed to the exporter, but that have not been exported yet (neither successful, nor failed).