4K image prices: FLUX.3 is 6.07x its 2K, Nano Banana 2.1 on Sume 1.33x

The cost of going from 2K to 4K varies a lot between image APIs. On Black Forest Labs' FLUX.3 Image, a 4K image is $0.607 against $0.100 for 2K, which is 6.07 times as much. On Google's Nano Banana 2.1, 4K is $0.113 against $0.0504 for 2K (2.24 times). On Sume, Nano Banana 2.1 moves from $0.15 at 2K to $0.20 at 4K (1.33 times), and Nano Banana Pro stays at $0.1875 for 1K and 2K and goes to $0.375 at 4K.

Sume does not list FLUX.3 Image yet; its catalog lists flux-2 rows. The FLUX.3 numbers come from BFL's pricing page for reference.

Price ladders, side by side

Each row is the vendor's published price per image for the three tiers, with the 4K ratio to the lower tiers computed here. BFL lists FLUX.3 as 768sq, 1k (about 1 megapixel), 2k (about 4 megapixels) and 4k (about 16 megapixels); the 1k and 2k columns below use those.

Why the ladders differ

Google bills tokens, and a 4K image is 3,780 output tokens against 1,680 for 2K, so the 4K price is rooted in token counts. BFL bills credits by resolution and the 4K tier is about 16 megapixels, which is four times the area of 2K, but the price is six times higher. Sume's Nano Banana rows are fixed list prices per tier, which flattens the curve relative to Google's: at 1K Sume is $0.10 against Google's $0.0336, and at 4K it is $0.20 against $0.113.

That makes Sume comparatively attractive at 4K and comparatively expensive at 1K, relative to Google direct. A workload that is mostly 4K narrows the gap to 1.77x ($0.20 / $0.113); a workload that is mostly 1K widens it to 2.98x ($0.10 / $0.0336).

Using it

If you generate many 4K images, price them at the 4K tier, not the headline 1K number. A batch of 200 4K images is 200 x $0.20 = $40.00 on Sume Nano Banana 2.1, 200 x $0.113 = $22.60 on Google Standard, and 200 x $0.607 = $121.40 on FLUX.3 Image. Quality and style differ between these models, so the cheapest row is not automatically the right one, but the table makes the cost side of the trade explicit.

Reading the 2K to 4K step

The ratio matters more than the headline price when you are choosing a default resolution. On a flat ladder such as Sume's Nano Banana 2.1 ($0.15 to $0.20), asking for 4K when you are unsure costs 5 cents extra per image. On a steep ladder such as FLUX.3 Image ($0.100 to $0.607), the same habit costs 50.7 cents extra per image, so 100 images at the wrong tier waste $50.70.

The practical rule is to choose the tier from the delivery size, not from habit: a 1080 x 1920 vertical needs less than 2K on the long edge, and a 3840 x 2160 thumbnail is the only case in this table where 4K is clearly required.