Seedream 4.0 ref2i vs 4.5 ref2i: Is the Older One Worth It

bytedance/seedream-4.0-ref2i is on Siray at $0.024 per image with a 20% discount applied, next to bytedance/seedream-4.5-ref2i at $0.04. Comparing the two OpenAPI specs with diff produces one changed line: the model enum. Every field, every constraint, and every accepted value is otherwise identical. The documentation cannot settle this choice, because as far as the documentation goes the two endpoints are the same endpoint.

Key TakeawaysBoth endpoints take the same four required fields: model, prompt, images (1 to 10 reference images), and size.The diff between their specs is one line long. The difference is the model weights, not the API surface.4.0 ref2i is $0.024 per image at a 20% discount (list $0.03). 4.5 ref2i is $0.04 with no discount — a 40% gap today, 25% at list.Neither endpoint has seed, n, or negative_prompt. Consistency comes from the images array, not from locking a seed.Pricing discounts can be withdrawn, so the list column is the number to plan against.

The Specs Are Identical. That Is the Whole Story

POST /v1/images/generations/async on both. Required on both: model, prompt, images — an array of 1 to 10 URLs or data URLs — and size.

size is not an aspect-ratio enum. It is eight fixed pixel strings: 2048x2048, 2304x1728, 1728x2304, 2560x1440, 1440x2560, 2496x1664, 1664x2496, and 3024x1296, up to a 3024 long edge. Switching versions does not change a single one of them.

There is no seed, no n, no negative_prompt, and no aspect_ratio on either endpoint. A workflow built on 4.0 transfers to 4.5 without a single edit.

What the Price Gap Actually Is

The headline gap is 40%, but only while the discount holds. At list the two are $0.03 and $0.04 — a 25% difference. The discount is promotional and can be withdrawn, so plan with the list column and treat the discount as margin.

Where the Older One Wins

Volume without a version-specific need. If a workflow feeds references, takes what comes back, and sends the output through a downscale, crop, or edit pass afterwards, the 40% saving compounds across every image: a thousand images is $24 instead of $40.

Iteration is the other case. Because consistency comes from the reference images rather than a seed, exploring a look means generating variations, comparing them, and adjusting the references. When a round of exploration costs $0.024 an image instead of $0.04, more of those rounds fit in the same budget — and the mechanism being explored is identical on both endpoints.

Where 4.5 Earns Its Premium

A newer version exists for a reason, and the reason is inside the weights, where a spec diff cannot see it. This article makes no claim about which renders better; that needs a side-by-side run with the same references, which is cheap enough to do before committing either way.

What can be said is where the premium is worth testing first: work where the raw output is the deliverable, and campaigns where a fixed set of references has to hold across many shots. On a small batch the absolute difference is small — twenty images is $0.48 against $0.80 — so at that scale, test both rather than optimizing the rate.

The images Array Is Where Consistency Comes From

Since neither version has a seed, the reference array is the only consistency control either one offers. Both accept up to 10 images, and the practical structure is the same on both: a small number of clean, well-lit references covering the angles you need, rather than a larger set of near-duplicates. For the single-endpoint version of this workflow on 4.5, see Seedream 4.5 ref2i character consistency without a seed; for the wider family, see Seedream 4.5 and Seedream 4.0. A comparable older-versus-newer pricing decision within the same lineup appears in Seedream 4.5 Spicy vs 5.0 Pro Spicy.

Create your free Siray account and run the same references through both Seedream ref2i versions.

A Note on Compliance

Siray's NSFW and uncensored models generate legal, consensual adult content for verified adults only. CSAM and any other illegal content are refused with zero tolerance. Seedream 4.0 ref2i and 4.5 ref2i are third-party models from ByteDance available through Siray's API, not Siray-hosted models, and the same standard applies to everything generated with them.