Nano Banana Pro is the stronger first route when your requirement is Google's stable API, Search grounding, complex instructions, accurate text, factual layouts, or an explicit 1K/2K/4K output tier. Seedream 4.5 is the stronger first route when an existing BytePlus workflow needs 2–14 reference images, sequential generation, and a lower official price per successful output. Neither choice is a universal visual-quality winner.
This July 18, 2026 refresh is an audit of current official contracts, not a paid same-prompt image shootout. We did not run model-version-matched generations for this update. Google's product positioning and ByteDance's internal benchmark describe what each vendor claims; they do not prove which model will pass your prompts more often. The practical decision is therefore: choose the contract that fits the job, run a small acceptance test, and compare the cost of images you can actually ship.
| Your expensive failure is… | First route to test | Why | Stop rule |
|---|---|---|---|
| Wrong text, labels, factual relationships, or complex instructions | Nano Banana Pro | Google positions gemini-3-pro-image for professional assets, accurate text, factual visualizations, grounding, and complex work. | Do not keep paying Pro if a cheaper route repeatedly passes the same rubric. |
| A multi-reference catalog or a sequence of related variations | Seedream 4.5 | BytePlus documents 2–14 references and sequential output for seedream-4-5-251128. | Switch if retries, JPEG conversion, or manual repair erase the attempt-price advantage. |
| A 4K final asset inside a Google stack | Nano Banana Pro | Google exposes a selectable 4K tier and a stable current model ID. | Verify that 4K is actually required; do not pay for it when the delivery surface is 1K/2K. |
| A new ByteDance integration rather than an existing 4.5 pipeline | Benchmark 4.5 and the Seedream 5.0 family | Seedream 4.5 remains listed, but 5.0 Pro is now ByteDance's professional image model. | Do not lock a new build to 4.5 before testing the current successor. |
What the official contracts actually verify
The clean comparison begins with exact route ownership. Google's current model card names Nano Banana Pro's stable Gemini Developer API code as gemini-3-pro-image. The image-generation guide lists 1K, 2K, and 4K output, Thinking, Search grounding, and SynthID on generated images. It also documents a total ceiling of 14 references, but that number is not fourteen interchangeable character images: Pro's current sublimits are up to six high-fidelity object images, five character-consistency images, and three style references.
ByteDance's Seedream 4.5 page emphasizes improved reference-detail preservation, multi-image subject identification, typography, dense text, alignment, and aesthetics versus Seedream 4.0. That last clause matters: MagicBench is ByteDance's internal benchmark against its own earlier model. It is not a head-to-head win over Nano Banana Pro.
On the API side, BytePlus ModelArk currently lists seedream-4-5-251128 for text-to-image, single-image editing, multi-reference editing, and batch or sequential generation. Its multi-reference contract accepts 2–14 input images. For sequential output, input references plus generated images cannot exceed 15. Results can be returned as a URL or Base64; URLs expire after 24 hours. The documented output format for this 4.5 route is fixed to JPEG, while the watermark can be toggled.
| Contract item, checked July 18, 2026 | Nano Banana Pro | Seedream 4.5 | What not to infer |
|---|---|---|---|
| Current official ID | gemini-3-pro-image | seedream-4-5-251128 | A provider alias is not automatically the current official ID. |
| Output tiers | 1K, 2K, 4K | Current BytePlus image API supports the route's documented output sizing | “4K available” does not mean every call is 4K. |
| Reference inputs | Up to 14 total, with category sublimits | 2–14 for multi-reference generation | Neither “14” means fourteen people nor guarantees identity fidelity. |
| Distinctive contract | Search grounding, Thinking, SynthID | Sequential generation; input plus outputs capped at 15 | A feature listing is not an acceptance-rate result. |
| Output delivery | Gemini API response contract | URL or Base64; URL expires in 24 hours; JPEG output | Wrapper formats may differ from official routes. |
List price is not the cost of a usable asset
Google's current pricing table lists Nano Banana Pro standard image output at $0.134 for 1K/2K and $0.24 for 4K. Batch and Flex reduce those image-output figures to $0.067 and $0.12. The table lists no Free Tier for this model. Text, thinking, input-image, Search grounding, Priority, tax, and other charges can add to the bill.
BytePlus billing lists Seedream 4.5 at $0.04 per successfully generated image, with input images free. Outputs that fail because of moderation or other generation failures are not billed, and sequential generation bills the successful output count. These are BytePlus terms, not a promise about every Seedream wrapper.
For 1,000 successful outputs before review, the direct list-price arithmetic is straightforward:
| Official route scenario | Output-only list-price scenario | Boundary |
|---|---|---|
| Seedream 4.5 | $40 | Successful outputs on the checked BytePlus contract |
| Nano Banana Pro standard, 1K/2K | $134 | Other Gemini charges excluded |
| Nano Banana Pro standard, 4K | $240 | Other Gemini charges excluded |
| Nano Banana Pro Batch/Flex, 1K/2K | $67 | Asynchronous or Flex tradeoffs still apply |
| Nano Banana Pro Batch/Flex, 4K | $120 | Other Gemini charges excluded |
That table still does not tell you which workflow is cheaper. A generated image can be billable yet unusable because a price is wrong, a label moved, a product changed, or a reference identity drifted. Use this instead:
effective cost per accepted image = price per attempt / acceptance rate
For 100 accepted assets, let a_S be Seedream's acceptance rate and a_N Nano Banana Pro's acceptance rate, each expressed from 0 to 1:
- Seedream 4.5:
100 × $0.04 / a_S = $4 / a_S - Nano Banana Pro standard 1K/2K:
100 × $0.134 / a_N = $13.40 / a_N - Nano Banana Pro standard 4K:
100 × $0.24 / a_N = $24 / a_N - Nano Banana Pro Batch/Flex 1K/2K:
$6.70 / a_N - Nano Banana Pro Batch/Flex 4K:
$12 / a_N
This produces a useful break-even rule without inventing a quality score. Against Nano Banana Pro standard, Seedream remains cheaper at 1K/2K when a_S > 0.2985 × a_N; against Pro 4K, the threshold is a_S > 0.1667 × a_N. Against Batch/Flex, the corresponding thresholds are about 0.5970 × a_N and 0.3333 × a_N.
These equations are not a model benchmark. They tell you what acceptance rate your own logs must show before the cheaper attempt is also the cheaper deliverable.
Run an acceptance test that can change the decision
Do not compare one favorite screenshot from each model. Use the same prompt, reference files, target dimensions, and delivery constraints. Run at least three attempts per route. Three samples are a pilot, not statistical proof, but they are enough to catch an obvious contract mismatch before migration.
| Test card | Predeclared pass condition | Failure that should change the route |
|---|---|---|
| Exact text and factual layout | Every required character, number, label, connection, and hierarchy is correct. | A beautiful image with a wrong price or relationship fails. |
| Multi-reference identity | Required objects or characters retain the named details across the final composition. | A reference count within the API limit still fails if identity drifts. |
| Sequential variations | The requested number of related assets arrives with stable mandatory elements. | Retry volume or review time removes the batch advantage. |
| Final high-resolution asset | The requested tier is delivered and survives crop, zoom, and production export. | Stop paying for 4K if the destination never exposes the extra detail. |
Record four numbers for each route: attempted outputs, accepted outputs, manual repair minutes, and total provider bill. Count a result as accepted only if it can ship after your normal review. If a typo requires Photoshop, record the repair time rather than quietly calling the generation a pass.
A practical switch rule
- Start with the route whose documented contract matches the job.
- If a business-critical rule fails in two of the first three attempts, pause that route rather than prompting indefinitely.
- Test the alternative with the same inputs.
- Keep the route with the lower accepted-image cost after review time, not the route with the prettiest single sample.
- Re-run the pilot after a model version, provider mapping, price, or output contract changes.
When each model is the wrong default
Nano Banana Pro is the wrong default for cheap exploration when Search grounding, complex instruction handling, Pro text behavior, and 4K final output are not required. Its official image-output price can be rational for a high-cost final asset, but it is wasteful as an untested draft lane.
Seedream 4.5 is the wrong default when the fixed JPEG output, region availability, or sequential contract conflicts with your pipeline; when your acceptance rate falls below the break-even threshold; or when a new ByteDance build would be better served by testing the current Seedream 5.0 family. BytePlus still lists 4.5 and does not label it deactivated, so existing pipelines do not need a panic migration. New projects should not treat “still available” as “best current starting point.”
Both are the wrong default when the wrapper cannot prove the actual upstream model, billing unit, failure billing, logs, support boundary, or data terms. Stop before production if those fields are ambiguous.
Official direct access or a gateway?
Use Google or BytePlus directly when first-party billing, model identity, support, regional controls, and data terms are part of the requirement. Official documentation owns the model IDs and first-party price rows quoted above.
A multi-model gateway can still help when the job is simpler switching, pay-as-you-go access, or one integration for a controlled pilot. Current public laozhang.ai documentation exposes pages for both Nano Banana Pro and Seedream image routes. However, the Nano Banana Pro page still shows an older preview alias while Google now documents stable gemini-3-pro-image. Treat that mismatch as a verification requirement: check the live model list, response metadata, billing unit, and console before integration. Do not present the gateway alias as settled or its provider price as Google's official price.
If you are choosing a newer cost-oriented pair rather than this exact Pro-versus-4.5 job, continue with Nano Banana 2 vs Seedream 5.0 Lite. For a wider model shortlist, use the 2026 AI image API comparison.
Bottom line
Choose Nano Banana Pro first for Google's stable professional route, Search grounding, complex instructions, factual or text-sensitive assets, and explicit 4K delivery. Choose Seedream 4.5 first for an existing BytePlus multi-reference or sequential workflow where $0.04 successful outputs matter. For a new ByteDance build, include Seedream 5.0 in the pilot.
Then let your acceptance log overrule the headline. The cheapest attempt is only the cheapest model when enough outputs pass review—and no official feature table or vendor benchmark can calculate that rate for your assets.
