After having removed 4K support last year, Hulu is once again streaming in 4K resolution. It is supported on Apple TV 4K and Chromecast Ultra.
But no High Dynamic Range
Hulu launched in 4K streaming support in late 2016 but quietly removed the feature in early 2018. At that time, it was supported on Xbox One and PlayStation 4 Pro.
Hulu is now bringing back 4K support to its service but there are some changes. At relaunch, it is supported on Apple TV 4K and Chromecast Ultra only - not game consoles. The company has not commented on the discrepancy.
The 4K library is limited to Hulu Originals such as The Handmaid’s Tale, Catch-22, The First, The Path, and Castle Rock. In 2016 it also included 20 James Bond movies but these are no longer available. Amazon and Netflix both offer a more expansive catalog of content in 4K resolution.

Hulu does not support HDR (High Dynamic Range) in any form at this time but the streaming service is now under Disney's wings. Disney has confirmed that its upcoming Disney+ streaming service will support 4K HDR and that Hulu will be kept alive as a separate service that will expand internationally. As such, things may change under Disney's leadership.
The company recommends at least 16Mb/s bandwidth for its 4K streams.
- Source: HuluThe Streamable