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Local Model Deployment

OhMyCaptcha supports running image recognition and classification tasks on a locally hosted model served via SGLang, vLLM, or any OpenAI-compatible inference server.

This guide covers deploying Qwen3.5-2B locally with SGLang.

Architecture: Local vs Cloud

OhMyCaptcha uses two model backends:

Backend Role Env vars Default
Local model Image recognition & classification (high-throughput, self-hosted) LOCAL_BASE_URL, LOCAL_API_KEY, LOCAL_MODEL http://localhost:30000/v1, EMPTY, Qwen/Qwen3.5-2B
Cloud model Audio transcription & complex reasoning (powerful remote API) CLOUD_BASE_URL, CLOUD_API_KEY, CLOUD_MODEL External endpoint, your key, gpt-5.4 
┌────────────────────────────────────────────────────────────┐
│                      OhMyCaptcha                            │
│                                                            │
│  Browser tasks ──► Playwright (reCAPTCHA, Turnstile)        │
│                                                            │
│  Image tasks ───► Local Model (SGLang / vLLM)               │
│                   └─ Qwen3.5-2B on localhost:30000          │
│                                                            │
│  Audio tasks ───► Cloud Model (remote API)                  │
│                   └─ gpt-5.4 via external endpoint          │
└────────────────────────────────────────────────────────────┘

Prerequisites

  • Python 3.10+
  • NVIDIA GPU with CUDA support (recommended: 8GB+ VRAM for Qwen3.5-2B)
  • pip package manager

Step 1: Install SGLang

pip install "sglang[all]>=0.4.6.post1"

Step 2: Launch the model server

From Hugging Face

python -m sglang.launch_server \
  --model-path Qwen/Qwen3.5-2B \
  --host 0.0.0.0 \
  --port 30000

export SGLANG_USE_MODELSCOPE=true
python -m sglang.launch_server \
  --model-path Qwen/Qwen3.5-2B \
  --host 0.0.0.0 \
  --port 30000

With multiple GPUs

python -m sglang.launch_server \
  --model-path Qwen/Qwen3.5-2B \
  --host 0.0.0.0 \
  --port 30000 \
  --tensor-parallel-size 2

Once started, the server exposes an OpenAI-compatible API at http://localhost:30000/v1.

Step 3: Verify the model server

curl http://localhost:30000/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "Qwen/Qwen3.5-2B",
    "messages": [{"role": "user", "content": "Hello"}],
    "max_tokens": 32
  }'

You should receive a valid JSON response with model output.

Step 4: Configure OhMyCaptcha

Set the local model env vars to point at your SGLang server:

# Local model (self-hosted via SGLang)
export LOCAL_BASE_URL="http://localhost:30000/v1"
export LOCAL_API_KEY="EMPTY"
export LOCAL_MODEL="Qwen/Qwen3.5-2B"

# Cloud model (remote API for audio transcription etc.)
export CLOUD_BASE_URL="https://your-api-endpoint/v1"
export CLOUD_API_KEY="sk-your-key"
export CLOUD_MODEL="gpt-5.4"

# Other config
export CLIENT_KEY="your-client-key"
export BROWSER_HEADLESS=true

Step 5: Start OhMyCaptcha

python main.py

The health endpoint shows both model backends:

curl http://localhost:8000/api/v1/health

{
  "status": "ok",
  "supported_task_types": ["RecaptchaV3TaskProxyless", "..."],
  "browser_headless": true,
  "cloud_model": "gpt-5.4",
  "local_model": "Qwen/Qwen3.5-2B"
}

Alternative: vLLM

vLLM can serve the same model with an identical API:

pip install vllm
python -m vllm.entrypoints.openai.api_server \
  --model Qwen/Qwen3.5-2B \
  --host 0.0.0.0 \
  --port 30000

No changes to the OhMyCaptcha configuration are needed — both SGLang and vLLM expose /v1/chat/completions.

Backward compatibility

The legacy environment variables (CAPTCHA_BASE_URL, CAPTCHA_API_KEY, CAPTCHA_MODEL, CAPTCHA_MULTIMODAL_MODEL) are still supported as fallbacks. If you set CAPTCHA_BASE_URL without setting CLOUD_BASE_URL, the old value will be used. The new LOCAL_* and CLOUD_* variables take precedence when set.

Model Size Use case VRAM
Qwen/Qwen3.5-2B 2B Image recognition & classification ~5 GB
Qwen/Qwen3.5-7B 7B Higher accuracy classification ~15 GB
Qwen/Qwen3.5-2B-FP8 2B (quantized) Lower VRAM requirement ~3 GB