You can learn more on the wiki:
On the video section of the website (Haxe Videos - Haxe - The Cross-platform Toolkit) you can find several talks about haxe 4:
- What’s new in haxe 4 by Andy Li at the Hong Kong Open Source Conference 2019
- Haxe 4 what’s new by Aleksandr Kuzmenko at the Haxe US Summit 2019
- Haxe 4.0 by Nicolas Cannasse at the Haxe US Summit 2018
Simon Krajewski did a talk Haxe Status Report at the in progress HaxeUp Linz 2019 (currently on twitch, will be uploaded to youtube later).