Old threshold: it takes 20% of row changes before auto update stats kicks (there are some tweaks for small tables, for large tables, 20% change is needed). For a table with 100 million rows, it requires 20 million row change for auto stats to kick in. For vast majority of large tables, auto stats basically doesn’t do much.
New threshold: Starting SQL 2008 R2 SP1, we introduced a trace flag 2371 to control auto update statistics better (new threshold). Under trace flag 2371, percentage of changes requires is dramatically reduced with large tables. In other words, trace flag 2371 can cause more frequent update. This new threshold is off by default and is enabled by the trace flag. But in SQL 2016, this new threshold is enabled by default for a database with compatibility level 130.
Important to know.