Seedream 5.5 vs Nano Banana 2.1: transparent assets or grounded visuals?

Choose Seedream 5.5 for evaluation when native transparent assets are a hard delivery requirement. Evaluate Nano Banana 2.1 when the task depends on Google’s documented search-grounded image generation. Both address conversational editing and text-bearing imagery; those shared capabilities do not establish a universal winner.

This is a documentation comparison checked November 12, 2026, not a same-prompt benchmark. Ofox publishes it and offers image-model services. We have not obtained new Seedream 5.5 outputs for this article. A vendor’s demonstration and our historical test of another model are different kinds of evidence.

Compare the actual deliverable

Sources: ByteDance’s 5.5 announcement and Google’s Nano Banana 2.1 model documentation. Absence from these sources is not proof that a feature is impossible; it means the feature cannot be treated as an established purchasing requirement here.

Reference inputs and controls are a separate decision

Google identifies the model as gemini-nano-banana-2.1, distinct from the older gemini-3.1-flash-image. Its model documentation lists 1K, 2K and 4K image output, configurable thinking, and fusion of up to 14 reference images. These documented controls matter when a brief combines product, character and style references. A maximum input count is not a guarantee that every reference detail will survive.

ByteDance’s 5.5 product page demonstrates reference-based transparent assets and successive edits, but that page does not specify an equivalent reference-image ceiling or API thinking control. Mark those fields as unverified rather than inventing matching settings. For a multi-reference job, Google’s published contract provides a clearer starting point; for an alpha asset, ByteDance provides the explicit native-output evidence.

The implementation paths also differ. Google’s current image-generation guide illustrates the Interactions API and continuing an edit through the previous interaction. An Ofox or other gateway may use a different route and response shape. A provider’s model listing does not establish support for all direct-Google controls. Compare the configuration actually exposed by the service you will use.

Read the vendor comparison correctly

ByteDance names Nano Banana 2.1 among its comparison models. Its published preference results concern particular realism and text-structure tasks. That is useful evidence of the vendor’s evaluation, not an independent finding that Seedream wins every creative job. Do not turn a preference score into a percentage of correct outputs, or infer speed and price from an image-quality chart.

Our existing GPT Image 2.6 comparison answers a different question involving GIF and SVG delivery. The presence of multiple competitors in a launch graphic does not make their versions interchangeable.

Transparent product artwork: specify the file, not just its appearance

Suppose a designer needs a glass ornament for a white catalog, a dark banner and a colored slide. The requirement includes partially transparent glass and clean fine edges. A model that produces a beautiful JPEG on white has not completed that job.

A reusable brief is:

Create one isolated glass ornament from the supplied reference.
Preserve the outline, hanging loop and etched design.
Deliver a PNG with a real alpha channel, including partial transparency
where the glass transmits light. No painted checkerboard, white rectangle,
background text or extra objects. Keep the entire object in frame.

This is an evaluation prompt, not a claimed successful generation. Confirm the selected interface supports alpha before spending on a batch. Then inspect the downloaded file rather than a browser screenshot. Composite it over white, black and a saturated color. Reject opaque rectangles, halos and missing fine parts. Use the transparent PNG guide for the file-checking procedure.

For an existing Nano Banana workflow, a separate background-removal step may remain practical. Treat that as a different production pipeline: include cleanup time and inspect semitransparent edges after removal. Do not label the composite workflow native RGBA generation.

Grounded campaign visuals: keep retrieval separate from approval

For a campaign tied to current product information, the important distinction is whether the generation route can retrieve relevant material. Google’s documented grounding creates a reason to evaluate Nano Banana 2.1 here. It does not authorize the model to invent stock levels, prices or discounts.

Prepare a dated fact sheet before rendering: approved product name, source URL, exact offer, expiration date and required disclaimer. Ask for a visual based on those approved facts. Any additional fact introduced by the model must return to review. A plausible chart with an unsupported number fails even if the photograph is excellent.

Keep application-level brand features separate from raw API capabilities. Retain the approved brand reference and fact sheet with each production job; do not assume another application’s stored brand context is available in Ofox Chat or an API request.

Continuous editing: prevent the test itself from changing

Use the same owned reference, approved text and requested change for both candidates. First change only the background. Next change one material. Finally change a specified object color. Preserve the original and every intermediate result; use each model’s own preceding output for its next revision.

Evaluate four separate questions: did the requested region change; did protected details remain; is the text exact; is the final file usable? A single attractive result cannot answer all four. Keep rejected attempts in the record rather than selecting one favorite per model. The multi-turn editing guide explains how to track drift.

Access, cost and failures

Verify the model name in the actual service. Our Nano Banana 2.1 API guide distinguishes the 2.1 route from the older Nano Banana 2 identifier. The Seedream access guide separates vendor announcements from Ofox availability; its dated observations must not be treated as a perpetual catalog guarantee.

For Ofox integration, consult the Nano Banana endpoint and response documentation and Seedream request, size and editing documentation. These describe Ofox routes separately from the model vendors’ APIs. The Seedream page currently documents older versions; its existence does not confirm 5.5 support or an alpha-output contract.

There is no verified equal-task price comparison in this article. Calculate total generation charges divided by accepted assets, then record editing labor separately. For example, a hypothetical $6 batch yielding 12 accepted assets costs $0.50 each before labor; a $4 batch yielding four costs $1. These are arithmetic examples, not model prices.

If an API completes without an image, inspect the returned parts and finish reason before changing models. Use the Nano Banana no-image troubleshooting article. A successful HTTP response is not proof of an image deliverable, and a failed request is not proof of poor visual quality.

Practical choice

For transparent reusable artwork, evaluate the explicitly documented alpha route first. For current-information visuals, evaluate the documented grounded route first. For ordinary product editing, there is no justified universal ranking in the evidence gathered here: the deciding factor is preservation of the details your customer will actually inspect. Keep brand styling, factual correctness and exported file validity as separate acceptance decisions.