Here's what the official material says. Flash has been in limited early access since Sept 28, and the official entry point's notice points to Ultra annual subscribers. For the full model, the release notes say it launches in October, while the Sept 30 introduction says it enters early access first and expands in October. I couldn't find evidence that every regular account has full 4.0 access, but it's also wrong to say nobody can use it. It depends on your account.

Two items are explicitly still coming soon: 10-bit HDR at 1080p/4K, and multiple extensions up to 2 minutes.

5. Who should care

By task, 4.0 is most relevant if you:

● need longer continuous shots, or short stories and previs with a clear arc
● need complex character motion or performance clips
● need several references at once to keep a character or product consistent
● want keyframes to control timing
● make ads, music videos or performance shots
● have multilingual dialogue where voice and lip-sync need to line up

If you mostly make simple 5–10s clips, basic image-to-video or quick idea tests, 3.0 is still fine. There's no need to upgrade just for the version number, and 4.0 coming out doesn't make 3.0 useless.

References:

The information above about Kling 4.0 comes from kling4.tv.

● Kling 4.0 official release notes
● Kling VIDEO 3.0 / 3.0 Omni official guides
● Kling 4.0 feature page and multi-keyframe guide

A question for anyone who already has access to 4.0 full or Flash: on 20–30s continuous action, do the characters and motion stay consistent all the way through? And once you go past five or six keyframes, does it get more controllable or do they start fighting each other? Official specs are one thing; what actually comes out is another.