FLUX 3 is a third-party video generation model from Black Forest Labs, available on Runway. It's built for long, continuous single-take shots — for example, you can generate an unbroken 20-second dolly through a crowded market without the cut-aways other models fall back on. FLUX 3 also handles a wide stylistic range, from photoreal to stylized looks, with naturalistic motion and physical coherence.

This article covers how to access FLUX 3 in Custom mode, prompt and input best practices, available settings, and what to expect from your generations.

Spec Information

Step 1 – Selecting FLUX 3

The model picker lives at the bottom of the generation panel. FLUX 3 is available in Custom, Workflows, and Apps.

1. From the left sidebar, click Custom.
2. Select the Video tab at the top of the generation panel.
3. Click the model dropdown at the bottom of the panel and type in the search bar FLUX 3.

Step 2 – Writing the prompt

Your prompt will vary depending on your inputs and what you're trying to accomplish. In any creation mode or model, we recommend using positive, unambiguous, and outcome-focused language. FLUX 3 responds well to prompts that describe a single continuous shot, so lean into camera movement, subject action, and how the scene evolves over time.

Using the reference inputs

Write your prompt as if you're describing the scene you want to appear, as well as how each input should be used.

• Keyframes — add a first frame, or both a first and last frame, then describe the motion, camera behavior, and transitions that should carry the shot between them
• Image references — add up to 10 images to guide the subject, style, or setting, and describe how each should appear in the shot, including its action and how the camera treats it

Note: Keyframes cannot be combined with reference inputs.

Tip: FLUX 3 is built for long, uninterrupted single-take shots up to 20 seconds. If you want a continuous moment rather than a series of cuts, write your prompt as one evolving beat — a sustained camera move, a single action unfolding, or a gradual shift in the scene.

Step 3 – Generating with FLUX 3

Before generating, review your settings:

• Prompt — describe the video you want to generate, including how each reference should be used
• Inputs — confirm your keyframes or references meet the requirements in the Spec Information table, and remember that keyframes and references cannot be combined
• Aspect ratio — choose from 21:9, 16:9, 4:3, 1:1, 3:4, 9:16, or 9:21
• Duration — set between 5 and 20 seconds
• Resolution — choose 480p or 720p

Credit cost is driven by your duration selection at 17 credits per second. See the Spec Information table for the full breakdown..

Once your prompt and settings are ready, select Generate.

Next steps

Once you've generated with FLUX 3, keep working with your output:

• Edit Studio — Edit your generation without starting over: swap subjects, adjust lighting, or restyle the shot with Aleph 2.0 while keeping the motion you liked.
• Upscale Video — Increase the resolution of your finished clip for final delivery.