Real-time Transaction Monitoring (RTTM) metrics, formerly BtStats, are now Customer Experience Metrics. The term RTTM is still used in the APM documentation.
I am looking at the APM documentation such as APM Metrics. I see no mention of RTTM Metrics.
This is in all APM 10.x documentation
A little further down in the documentation is a section called Customer Experience Metrics. This is the new name for RTTM metrics to include other functionality besides RTTM. RTTM and Real-time Transaction Metrics are still in the APM documentation.