Blog / Models, 2026-04-30, 9 min read
Imagen 4 (Retired) vs Flux: Which AI Image Model Should You Pick?
Update, September 6, 2026: Google retired Imagen 4 (Standard, Fast and Ultra) on August 17, 2026. On Viral Engine, Nano Banana Pro (80 credits) takes over the Ultra work this guide compares against Flux, Nano Banana 2 (40 credits) covers Standard and Fast, and GPT Image 2 (25 credits) is now the pick for in-image text. Flux itself is 12 credits per image. The comparison below is kept for reference with the recommendations updated. Retirement details.
Two of the strongest image models of 2026 sat at opposite ends of the philosophy spectrum. Imagen 4 is Google's closed-weights flagship: maximum photorealism, three quality tiers, generated through Google's API. Flux is Black Forest Labs' open-weights model: maximum creative control, seed locking, image-to-image, inpainting, outpainting, at the cheapest credit cost on the platform.
Nano Banana Pro and Flux are both on Viral Engine. This guide covers when to pick each one with cost math and real prompt examples.
The 30-second answer
- Photorealistic hero shots and portraits: Nano Banana Pro.
- Reproducible variations and seed-locked iteration: Flux.
- Inpainting and outpainting: Flux.
- High volume on a budget: Flux (12 credits per image).
- In-image text and signage: GPT Image 2, or Nano Banana Pro.
- Image-to-image with adjustable strength: Flux.
Side-by-side
| Dimension | Nano Banana Pro | Flux |
|---|---|---|
| Photorealism (1-10) | 10 | 8 |
| Creative control | Low | High |
| Seed locking | No | Yes |
| Image-to-image | Limited | Yes (adjustable strength) |
| Inpainting | No | Yes (brush) |
| Outpainting | No | Yes (canvas expand) |
| In-image text | Best in class | Good |
| Cost per image | 80 credits | 12 credits |
| Speed (1-10) | 5 | 7 |
Cost math: $14/month, what does it buy?
Essential plan, 4,000 credits:
- Nano Banana Pro: 50 hero-tier images per month.
- Flux: 333 images per month at 1K, 222 at 2K, 166 at 4K.
If you need 200+ images per month, Flux is the only economical choice. If you need 50 hero-tier images, Nano Banana Pro is the right pick.
When Imagen 4 wins
Anywhere the output is the deliverable, not a step:
- Brand hero shots. Skin texture, surface accuracy, lighting fidelity. Nano Banana Pro's photorealism ceiling is the reason it exists.
- Portrait closeups. Hands, faces, eye contact. The classic AI failure modes that Imagen 4 substantially fixes.
- In-image typography. Logos, product labels, headlines. Quote the exact text in the prompt and Imagen 4 renders it cleanly.
- Print and large-format. Detail holds up at scale; Flux can show artifacts when blown up beyond ~2K.
When Flux wins
Anywhere the workflow needs control or repeatability:
- Seed-locked variations. Generate one composition you like, lock the seed, change small prompt details. Same composition, controlled variations. Imagen 4 has no equivalent.
- Image-to-image refinement. Upload a draft, dial denoising strength, transform style or lighting while preserving composition.
- Inpainting fixes. When 90% of an image is right and 10% needs surgery (a malformed hand, a wrong product label, a cluttered background corner). Brush mask, regenerate just that region.
- Aspect-ratio expansion. Outpaint a portrait into a 16:9 banner without re-shooting.
- Volume at low cost. 12 credits per image is the lowest price on the platform.
The workflow we use
Internally, we don't pick one or the other; we chain them.
- Generate 4 variations on Flux (cheap, fast, gives composition options).
- Pick the strongest, lock the seed.
- Refine the prompt and re-generate on Flux 2-3 more times until composition is dialed.
- Take that final composition and feed it as image-to-image into Flux at low denoising strength to lock it in.
- For the absolute final hero, regenerate the prompt on Nano Banana Pro. Pick the best.
Total cost per finished hero: 164 to 176 credits (four Flux explorations, two or three refinements and one image-to-image pass at 12 credits each, plus one Nano Banana Pro finish at 80). Versus 640 to 720 credits if you run the same eight or nine rounds on Nano Banana Pro from scratch hoping for a hit.
Prompt example: same brief, both models
Brief: Editorial portrait of a woman in her 40s, auburn shoulder-length hair, soft north-window light, emerald velvet backdrop, 85mm.
Flux output: Strong composition, accurate lighting, clean velvet texture. Slight softness on facial micro-detail. 12 credits.
Nano Banana Pro output: Clinical portrait quality, every pore and hair strand resolved, perfect eye reflection. Print-ready. 80 credits.
For a magazine cover, use Nano Banana Pro. For an Instagram post, Flux is more than enough.
Open weights vs closed weights, does it matter?
For most users on Viral Engine, no. Both run server-side. You generate, download, ship. The open-weights distinction matters if:
- You want to fine-tune the model on your own dataset (Flux supports this; Imagen 4 doesn't).
- You want to run the model locally with no platform dependency (Flux runnable; Imagen 4 not).
- You're sensitive to vendor lock-in concerns at the model layer.
Otherwise, both feel identical from inside the dashboard.
Bottom line
Pick Flux when you need control or volume. Pick Nano Banana Pro when output is the deliverable. Or do what we do: chain them. Cheap iteration on Flux, finishing pass on Nano Banana Pro. The 200 free credits on signup let you test both before deciding.
More: Nano Banana 2 vs Imagen 4 (retired), prompt engineering guide, Imagen 4 deep dive, Flux deep dive