There is no 1GB limit. I think you might be confused about compute units? Compute units are just a measure of RAM usage over time -- a compute unit is 1GB of RAM used for one hour. An app can use more than 1GB of RAM; it will just consume compute units faster. E.g. an app using 2GB will consume a compute unit in 30 minutes.

This all relates to our upcoming managed hosting. Self-hosted installs are not metered since it's your own hardware.

https://blog.sandstorm.io/news/2015-01-14-compute-units.html