DNE auto restriping introduced in Lustre-2.14.0 and it can be managed by the following parameters.

e.g.
mdt.*.enable_dir_auto_split=1
mdt.*.dir_split_count=50000
mdt.*.dir_split_delta=4

However, it still needs to issue "stat <dir>" to trigger restriping and doesn't split during file creation today.
It would add a policy to split metadata across MDTs without "stat" call to directory and it triggers metadata splitting automatically even during file creation.