As expected, Apple has released the fourth beta of iOS 7 this morning. The update comes three weeks after the release of beta 3—longer than the the time period between previous betas due to a lengthy Developer Center outage caused by a security breach.
Beta 4 is available now to all registered Apple developers via OTA (over the air update), which can be installed by visiting the Software Update section in the Settings app of devices that currently have iOS 7 installed. And it should post soon to the dev portal...