OpenAI-Compatible HTTP Adapter for ComfyUI

Small FastAPI bridge that exposes POST /v1/images/generations (OpenAI format) and maps it to ComfyUI's POST /api/prompt.

When to use

OpenWebUI, Bifrost, or any other tool that speaks OpenAI /v1/images/generations needs to generate images with ComfyUI.
ComfyUI itself has no native OpenAI-compatible endpoint.
The adapter is especially useful for FLUX.2 workflows that OpenWebUI's built-in ComfyUI connector cannot handle (different nodes: Qwen3VL, EmptyFlux2LatentImage, TAEF2).

Architecture

OpenWebUI / Bifrost / Client
   POST /v1/images/generations
            |
            v
   [FastAPI Adapter]  (Docker or systemd)
            |
            v
   POST http://<comfyui>:8188/api/prompt
   GET  http://<comfyui>:8188/history/<prompt_id>
   GET  http://<comfyui>:8188/view

Example: Minimal FLUX.2 Adapter (Docker)

`Dockerfile`

FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY adapter.py .
EXPOSE 9000
CMD ["uvicorn", "adapter:app", "--host", "0.0.0.0", "--port", "9000"]

`requirements.txt`

fastapi>=0.110.0
uvicorn>=0.29.0
httpx>=0.27.0
pydantic>=2.0.0

`adapter.py` — FLUX.2 Variant

The node names must match what is installed on the target ComfyUI instance. Query the running server first with GET /object_info to confirm.

Key requirements for FLUX.2:

CLIPLoaderGGUF with "type": "flux2" (loads Qwen3VL)
EmptyFlux2LatentImage (128-channel latents)
VAELoader with "vae_name": "taef2" (or dedicated flux2_vae.safetensors)
UnetLoaderGGUF with the FLUX.2 UNet GGUF

See scripts/adapter_flux2.py for a ready-to-use file.

Build & run

docker build -t comfyui-openai-adapter:latest .
docker run -d --name comfyui-openai-adapter --network host \
  -e COMFYUI_URL=http://10.0.30.97:8188 \
  -e WORKFLOW_PREFIX=oai_adapter \
  --restart unless-stopped \
  comfyui-openai-adapter:latest

Verifying node availability

Before deploying the adapter, confirm the target ComfyUI instance has the required nodes:

curl -s http://<comfyui>:8188/object_info | \
  python3 -c "import sys,json; d=json.load(sys.stdin); \
  [print(f'{n}: {n in d}') for n in \
  ['CLIPLoaderGGUF','UnetLoaderGGUF','EmptyFlux2LatentImage','VAELoader','KSampler']]"

OpenWebUI configuration

Admin Panel → Settings → Images → Image Generation

Setting	Value
Engine	`Open AI`
API Base URL	`http://<adapter-ip>:9000/v1`
API Key	dummy (adapter does not enforce auth)
Model	`flux2`

Bifrost integration

Bifrost is an LLM gateway with no native ComfyUI provider. The adapter fills that gap:

Register the adapter as an OpenAI-compatible provider in Bifrost, or
Point OpenWebUI directly at the adapter (recommended; keeps image path separate from chat routing).

Pitfalls

Node names are exact. Use GET /object_info to verify every class_type exists; missing custom nodes produce cryptic "class_type not found" errors from ComfyUI.
Model names are exact and case-sensitive. flux-2-klein-9b-Q4_K_S.gguf != flux-2-klein-9b-q4_k_s.gguf.
TAEF2 vs full VAE. taef2 resolves tiny encoder/decoder pth files; the full flux2_vae.safetensors requires manual download from a gated repo.
Seed injection. Always rewrite the seed per image when n > 1; otherwise every image in the batch is identical.
Timeout tuning. FLUX.2 on ROCm gfx1150 takes ~110s for 1024x1024 @ 4 steps. Set wait_for_image timeout >= 300s.

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