/modal

name: modal-serverless-gpu
description: Serverless GPU cloud platform for running ML workloads. Use when you need on-demand GPU access without infrastructure management, deploying ML models as APIs, or running batch jobs with automatic scaling.
version: 1.0.0
author: Orchestra Research
license: MIT
tags: [Infrastructure, Serverless, GPU, Cloud, Deployment, Modal]
dependencies: [modal>=0.64.0]

Modal Serverless GPU

Comprehensive guide to running ML workloads on Modal's serverless GPU cloud platform.

When to use Modal

**Use Modal when:**

• Running GPU-intensive ML workloads without managing infrastructure
• Deploying ML models as auto-scaling APIs
• Running batch processing jobs (training, inference, data processing)
• Need pay-per-second GPU pricing without idle costs
• Prototyping ML applications quickly
• Running scheduled jobs (cron-like workloads)

**Key features:**

• **Serverless GPUs**: T4, L4, A10G, L40S, A100, H100, H200, B200 on-demand
• **Python-native**: Define infrastructure in Python code, no YAML
• **Auto-scaling**: Scale to zero, scale to 100+ GPUs instantly
• **Sub-second cold starts**: Rust-based infrastructure for fast container launches
• **Container caching**: Image layers cached for rapid iteration
• **Web endpoints**: Deploy functions as REST APIs with zero-downtime updates

**Use alternatives instead:**

• **RunPod**: For longer-running pods with persistent state
• **Lambda Labs**: For reserved GPU instances
• **SkyPilot**: For multi-cloud orchestration and cost optimization
• **Kubernetes**: For complex multi-service architectures

Quick start

Installation

pip install modal
modal setup  # Opens browser for authentication

Hello World with GPU

import modal

app = modal.App("hello-gpu")

@app.function(gpu="T4")
def gpu_info():
    import subprocess
    return subprocess.run(["nvidia-smi"], capture_output=True, text=True).stdout

@app.local_entrypoint()
def main():
    print(gpu_info.remote())

Run: `modal run hello_gpu.py`

Basic inference endpoint

import modal

app = modal.App("text-generation")
image = modal.Image.debian_slim().pip_install("transformers", "torch", "accelerate")

@app.cls(gpu="A10G", image=image)
class TextGenerator:
    @modal.enter()
    def load_model(self):
        from transformers import pipeline
        self.pipe = pipeline("text-generation", model="gpt2", device=0)

    @modal.method()
    def generate(self, prompt: str) -> str:
        return self.pipe(prompt, max_length=100)[0]["generated_text"]

@app.local_entrypoint()
def main():
    print(TextGenerator().generate.remote("Hello, world"))

Core concepts

Key components

| Component | Purpose | |-----------|---------| | `App` | Container for functions and resources | | `Function` | Serverless function with compute specs | | `Cls` | Class-based functions with lifecycle hooks | | `Image` | Container image definition | | `Volume` | Persistent storage for models/data | | `Secret` | Secure credential storage |

Execution modes

| Command | Description | |---------|-------------| | `modal run script.py` | Execute and exit | | `modal serve script.py` | Development with live reload | | `modal deploy script.py` | Persistent cloud deployment |

GPU configuration

Available GPUs

| GPU | VRAM | Best For | |-----|------|----------| | `T4` | 16GB | Budget inference, small models | | `L4` | 24GB | Inference, Ada Lovelace arch | | `A10G` | 24GB | Training/inference, 3.3x faster than T4 | | `L40S` | 48GB | Recommended for inference (best cost/perf) | | `A100-40GB` | 40GB | Large model training | | `A100-80GB` | 80GB | Very large models | | `H100` | 80GB | Fastest, FP8 + Transformer Engine | | `H200` | 141GB | Auto-upgrade from H100, 4.8TB/s bandwidth | | `B200` | Latest | Blackwell architecture |

GPU specification patterns

# Single GPU
@app.function(gpu="A100")

# Specific memory variant
@app.function(gpu="A100-80GB")

# Multiple GPUs (up to 8)
@app.function(gpu="H100:4")

# GPU with fallbacks
@app.function(gpu=["H100", "A100", "L40S"])

# Any available GPU
@app.function(gpu="any")

Container images

# Basic image with pip
image = modal.Image.debian_slim(python_version="3.11").pip_install(
    "torch==2.1.0", "transformers==4.36.0", "accelerate"
)

# From CUDA base
image = modal.Image.from_registry(
    "nvidia/cuda:12.1.0-cudnn8-devel-ubuntu22.04",
    add_python="3.11"
).pip_install("torch", "transformers")

# With system packages
image = modal.Image.debian_slim().apt_install("git", "ffmpeg").pip_install("whisper")

Persistent storage

volume = modal.Volume.from_name("model-cache", create_if_missing=True)

@app.function(gpu="A10G", volumes={"/models": volume})
def load_model():
    import os
    model_path = "/models/llama-7b"
    if not os.path.exists(model_path):
        model = download_model()
        model.save_pretrained(model_path)
        volume.commit()  # Persist changes
    return load_from_path(model_path)

Web endpoints

FastAPI endpoint decorator

@app.function()
@modal.fastapi_endpoint(method="POST")
def predict(text: str) -> dict:
    return {"result": model.predict(text)}

Full ASGI app

from fastapi import FastAPI
web_app = FastAPI()

@web_app.post("/predict")
async def predict(text: str):
    return {"result": await model.predict.remote.aio(text)}

@app.function()
@modal.asgi_app()
def fastapi_app():
    return web_app

Web endpoint types

| Decorator | Use Case | |-----------|----------| | `@modal.fastapi_endpoint()` | Simple function → API | | `@modal.asgi_app()` | Full FastAPI/Starlette apps | | `@modal.wsgi_app()` | Django/Flask apps | | `@modal.web_server(port)` | Arbitrary HTTP servers |

Dynamic batching

@app.function()
@modal.batched(max_batch_size=32, wait_ms=100)
async def batch_predict(inputs: list[str]) -> list[dict]:
    # Inputs automatically batched
    return model.batc