What is the maximum size of an iOS application?

As of February 12, 2015

The size limit of an app package submitted through iTunes Connect has increased from 2 GB to 4 GB, so you can include more media in your submission and provide a more complete, rich user experience upon installation. Please keep in mind that this change does not affect the cellular network delivery size limit of 100 MB.

This information can be found on Apple news “Now Accepting Larger Binaries“.