"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Apple Seeds Fourth Beta of iOS 11.4.1 to Developers and Public Beta Testers
Registered developers can download the new iOS 11.4.1 beta from Apple's Developer Center or over-the-air once the proper configuration profile has been installed from the Developer Center. Public beta testers can also install the update over-the-air with the public beta profile.
No new features were discovered in the first three iOS 11.4.1 betas, suggesting it focuses on bug fixes and performance improvements to address issues discovered since the release of iOS 11.4.
We'll update this post should we discover any new features in the fourth iOS 11.4.1 beta, but we're not expecting major changes now that Apple has shifted its focus to iOS 12, which is also available to developers for beta testing purposes.