Mixer AI
Kling 4.0 Flash vs Kling 2.1: specs and price
Kling 4.0 Flash — maximum duration: 20 s; input photos: up to 7. Kling 2.1 — last frame: Yes.
When to choose Kling 4.0 Flash and when Kling 2.1
Kling 4.0 Flash
- Maximum duration: 20 s vs 10 s for Kling 2.1
- Input photos: up to 7 vs No for Kling 2.1
- Input videos: up to 5 vs No for Kling 2.1
- Prompt limit: 8,000 characters vs 5,000 characters for Kling 2.1
Kling 2.1
- Last frame: Yes vs No for Kling 4.0 Flash
Key differences
Specifications
| Spec | Kling 4.0 Flash | Kling 2.1 |
|---|---|---|
| Model variants | Flash | Standard / Pro / Master |
| Generation modes | from text / from first frame / from references | from text / from first and last frames |
| First frame | Yes | Yes |
| Last frame | No | Yes |
| Input photos | up to 7 | No |
| Input videos | up to 5 | No |
| Minimum duration | 3 s | 5 s |
| Maximum duration | 20 s | 10 s |
| Resolutions | 720p | No separate selector |
| Aspect ratios | 9:16 / 16:9 / 1:1 / auto / 21:9 | 9:16 / 16:9 / 1:1 |
| Prompt limit | 8,000 characters | 5,000 characters |
| Price (different settings) | — coins · 5 s · 720p | — coins · 5 s · No separate selector |
There is no shared resolution for a direct price comparison, so each price includes its setting and is not highlighted as cheaper.
Price at the same settings
What to compare visually
For a fair A/B test, use the same scene and, where both modes allow it, the same first frame. Inspect motion continuity, character and object consistency, physics and contacts, camera behavior, temporal deformation, in-clip cuts and audio synchronization.
What to inspect with Kling 4.0 Flash
A lighter Kling 4.0: clips of 3–20 seconds in 720p from text and references, or from a start frame.
- Text and references: a prompt up to 8000 characters, up to 7 photos and up to 5 videos totaling up to 20 seconds; the Video sound switch keeps the sound of reference videos.
- Start frame: one optional photo; without it choose 16:9, 9:16, 1:1 or 21:9, with it the format follows the photo.
- Flash gives 720p and up to 20 seconds only; choose Kling 4.0 for 1080p and 30 seconds.
- Start frame mode accepts no video: videos belong to references mode only.
What to inspect with Kling 2.1
Turn a photo into a short moving shot, or start from text with Master.
- Standard: one photo. Pro: one or two photos. Master: text or one photo.
- Choose 5 or 10 seconds. A separate negative-prompt field is available.
- Standard and Pro cannot start from text alone.
- Complex hand movements and sharp turns need close inspection.
How to run a fair comparison
- Fix the scene, the first frame (if both models accept one), the duration and the resolution.
- Judge motion, not stills: faces, hands and objects should hold across the whole clip and at cuts.
- If sound matters, listen to it separately: dialogue, effects and lip sync differ between models.
- Price a finished clip, not a second: the per-second rate times your real duration, rounded up once.
Sources
Prices, availability and specifications come from the Mixer AI catalog. This is not an independent test: try both models on the same task before choosing.
What we compare
FAQ
Which is cheaper: Kling 4.0 Flash or Kling 2.1?
The models use different settings, so a direct price comparison would be misleading: the prices of Kling 4.0 Flash and Kling 2.1 are in the table, so compare for the mode you need.
How does Kling 4.0 Flash differ from Kling 2.1?
Kling 4.0 Flash — maximum duration: 20 s; input photos: up to 7; input videos: up to 5. Kling 2.1 — last frame: Yes.
How should I compare Kling 4.0 Flash and Kling 2.1 fairly?
Fix the scene, first frame, duration and resolution. Watch the motion across the whole clip and listen to the sound separately. Price the finished clip, not one second.
Are both models available in Mixer AI?
Yes. Both models are in the Mixer AI video catalog; the launch button on the page opens Canvas on a computer and the Studio on a phone. The page exists only for models in the current catalog.
Which model is better?
There is no single winner. First rule out the model that lacks the duration, first or last frame, sound or resolution you need, then compare clips on your own scene. The table highlights only measurable differences.