Codex API image_generation silently ignores size/quality and returns gpt-image-2-codex auto output

What issue are you seeing?

Codex API image_generation silently ignores explicit size and quality parameters.

A request for gpt-image-2, quality=high, and size=2160x3040 is accepted through the Codex API / OAuth-backed image generation path, but the returned tool metadata is changed to:

• model=gpt-image-2-codex
• quality=auto
• size=auto

The final PNG is not 2160x3040.

This makes the Codex API image path unreliable for workflows that require deterministic output dimensions.

Expected behavior

Codex API should either honor the requested size and quality, or return a clear error if deterministic size / quality is not supported by the Codex API image generation path.

It should not silently downgrade the request while still returning success.

Requested parameters

{
  "type": "image_generation",
  "model": "gpt-image-2",
  "quality": "high",
  "size": "2160x3040",
  "output_format": "png"
}

Actual returned tool metadata

{
  "type": "image_generation",
  "model": "gpt-image-2-codex",
  "quality": "auto",
  "size": "auto",
  "output_format": "png"
}

Observed PNG dimensions

1024x1536
1054x1492
1058x1487
1254x1254
1693x929

Clarification

This issue is not about the native OpenAI Images API.

It is specifically about the Codex API / OAuth-backed image_generation path silently converting an explicit gpt-image-2 high/custom-size request into gpt-image-2-codex with quality=auto and size=auto.

What steps can reproduce the bug?

Send a Codex API / OAuth-backed image_generation request with explicit gpt-image-2, quality=high, and size=2160x3040.

Example request shape:

{
  "model": "gpt-5.5",
  "instructions": "Generate the requested image.",
  "input": [
    {
      "role": "user",
      "content": "Create a professional vertical research infographic. The output must be exactly 2160x3040 PNG."
    }
  ],
  "tools": [
    {
      "type": "image_generation",
      "model": "gpt-image-2",
      "quality": "high",
      "size": "2160x3040",
      "output_format": "png"
    }
  ],
  "tool_choice": {
    "type": "image_generation"
  },
  "store": false
}

Then inspect the returned response.created / response.completed tool metadata and the actual PNG dimensions.

Expected:

model=gpt-image-2
quality=high
size=2160x3040
PNG dimensions=2160x3040

Actual:

model=gpt-image-2-codex
quality=auto
size=auto
PNG dimensions are smaller than 2160x3040

What is the expected behavior?

Codex API should either honor the requested size and quality, or return a clear error if deterministic size / quality is not supported by the Codex API image generation path.

For a request with:

{
  "type": "image_generation",
  "model": "gpt-image-2",
  "quality": "high",
  "size": "2160x3040",
  "output_format": "png"
}

The expected output should preserve the requested parameters:

model=gpt-image-2
quality=high
size=2160x3040
PNG dimensions=2160x3040

If Codex API cannot support this, it should fail explicitly with a capability or validation error.

It should not silently convert the request to gpt-image-2-codex, quality=auto, size=auto, and return a smaller PNG while reporting success.

Additional information

_No response_