> ## Documentation Index
> Fetch the complete documentation index at: https://docs.apiyi.com/llms.txt
> Use this file to discover all available pages before exploring further.

# GPT Image 2.6 official relay: which output format and background combinations are invalid?

> For GPT Image 2.6 official relay (gpt-image-2.6-sunburst / gpt-image-2.6-flare): only transparent + jpeg returns 400, gif supports 1-bit transparency, and svg needs opaque for a background.

> [!NOTE]
>
> This page applies to the two **GPT Image 2.6 official-relay** models: `gpt-image-2.6-sunburst` (precision work) and `gpt-image-2.6-flare` (fast iteration). GPT Image 2.5 / 2 have no gif or svg output, so do not apply these rules to them directly.

## Short answer

There is exactly one hard conflict: `background: "transparent"` cannot be combined with `output_format: "jpeg"`; it returns 400. Every other combination works, but the transparency semantics differ:

| `background` | `png` | `jpeg` | `webp` | `gif` | `svg` |
| - | - | - | - | - | - |
| `transparent` | ✅ full alpha | ❌ 400 | ✅ full alpha | ✅ 1-bit transparency | ✅ no background |
| `opaque` | ✅ solid | ✅ solid | ✅ solid | ✅ solid | ✅ white background |
| `auto` | ✅ | ✅ | ✅ | ✅ | ✅ |

Measured on GPT Image 2.6 official relay on 2026-11-12 (`quality: "low"`, `n: 1`; GIF at 512×512 with 2 frames; SVG with `svg.model: "gpt-4.1-mini"`). The full matrix was measured on `gpt-image-2.6-sunburst`; `jpeg + transparent`, `gif + transparent`, and `svg + opaque` were re-checked on `gpt-image-2.6-flare` with identical results.

## JPEG is the only 400

JPEG has no alpha channel, so `background: "transparent"` fails with:

```text theme={null}
Transparent background is not supported for JPEG output format
```

This applies to both `/v1/images/generations` and `/v1/images/edits`. Switch to `png` / `webp` (or `gif` for animation); `opaque` and `auto` work fine with JPEG.

> [!WARNING]
>
> On the edit endpoint this 400 took about 62 seconds to return in our test (about 19 seconds on text-to-image), so do not retry just because the request seems slow.

## GIF supports transparency, but only 1-bit alpha

`output_format: "gif"` + `background: "transparent"` works on 2.6, on both text-to-image and image editing. Transparent pixels covered 46%–60% of the frame in our tests, versus 0% with `opaque`.

GIF transparency is palette-based: a pixel is either fully transparent or fully opaque, with no soft alpha edges. Use `png` / `webp` when edge quality matters. This only applies to 2.6, which supports GIF output; 2.5 and earlier do not support GIF output.

## SVG has no alpha; `opaque` adds a background

SVG is a vector format with no alpha channel, and transparency is the default:

* `transparent`: no background rectangle is written.
* `opaque`: a full-canvas white rectangle is added, such as `<rect width="1024" height="1024" fill="#fff" />`.
* `auto`: in both of our tests, `auto` wrote no background, so do not treat it as `opaque`; pass `opaque` explicitly when you need a white background.

> [!NOTE]
>
> `output_format: "svg"` is supported only on the text-to-image endpoint, requires `n: 1`, and requires `svg.model`. The author model decides the final background markup, so re-check the actual file after changing `svg.model`.

## `auto` is not fixed to `opaque`

`background` defaults to `auto` when omitted. `auto` follows the prompt rather than always producing a solid background:

* With a prompt that asks for a plain white background, `png` / `jpeg` / `gif` reported `opaque` and had no alpha.
* With a prompt that asks for an isolated subject on no background, `png` / `webp` / `gif` / `svg` reported `transparent`; the first three actually had transparent pixels.
* With `jpeg`, `auto` is forced to `opaque` and does not error.

For deterministic output, pass `transparent` or `opaque` explicitly instead of relying on `auto`.

## Two related format constraints

* `output_compression` only applies to `jpeg` / `webp`.
* `frame_count` / `frame_duration_ms` are only for `gif`; do not send them to PNG, JPEG, WebP, or SVG.

## Related docs

> [card] [GPT Image 2.6 capabilities](https://docs.apiyi.com/en/api-capabilities/gpt-image-2/gpt-image-2-6.md)
>
> SVG, GIF, `complexity`, and markup-guided editing with real results.

> [card] [How to generate transparent images](https://docs.apiyi.com/en/faq/image-transparent-background.md)
>
> Parameter shape, prompt requirements, and common errors for transparent backgrounds.

> [card] [Text-to-image API reference](https://docs.apiyi.com/en/api-capabilities/gpt-image-2/text-to-image.md)
>
> Every field for `/v1/images/generations`.

> [card] [Image editing API reference](https://docs.apiyi.com/en/api-capabilities/gpt-image-2/image-edit.md)
>
> `/v1/images/edits` and multi-image editing.


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