I've found simmilar question: Ace Editor autocomplete and multiple languages
But the responses were that autocompletion is not supported by ACE, and according to Google group for Ace Editor It is on my wishlish for Ace and we definitively need it
for Cloud9.
This post is one year old and as you can see, the cloud9 supports autocompletion now:
https://c9.io/site/features/
So is autocompletion available in Ace Editor by default? I cannot find any information about it.