Heungsub Lee

Contact
[email protected]
Web Sites
subl.ee, github.com/sublee, linkedin.com/in/sublee

Interest

AI services and platforms, real-time communication in distributed systems, cost and performance optimization, and developer experience.

Skills

Programming Languages
Go, Python, TypeScript
Service Development
Linux, AWS, gRPC, React, Pulumi, Kubernetes, Redis, ZeroMQ, Concurrent programming, Testing
AI Engineering
MCP, PyTorch, NCCL, NVIDIA Nsight Systems

Work Experience

Lead Software Engineer
Global AI Platform, Sep 2023 – Present

Leading the development of Aster, a personal AI agent service that applies planning to solve user problems by integrating data and functionalities from multiple MCP servers.

Directed LangDiff, an open-source library that bridges structured LLM outputs with progressive UI rendering.

Software Engineering Manager
NAVER, Aug 2020 – Jul 2023

Supervised 25 engineers on MLOps platforms to optimize inference performance and productivity for HyperCLOVA, a Korean-focused LLM.

Developed NSMLv2, a large-scale ML research platform at CLOVA. Designed a multi-tenant architecture with an economics-driven approach, enabling diverse organizations to share GPU clusters for HPC while maximizing resource efficiency.

Software Engineer
Kakao Brain, Dec 2018 – Aug 2020

Developed torchgpipe, an open-source pipeline parallelism library for PyTorch.

Developed a serverless training framework and distributed hyperparameter search pipelines for an AutoML service.

Game Server Engineer
NEXON, Mar 2011 – Dec 2018

Developed cloud-native distributed MMORPG servers for Durango using pub/sub over a spatial grid system, supporting up to 70k concurrent users per game world.

Developed online racing game servers and matchmaking for KartRider Dash and KartRider Coin Rush.

Back-end Web Developer
nPine, Dec 2008 – Feb 2011
Developed e-commerce web services for stock image platforms.

Open Source Experience

torchgpipe, Feb 2019 – Apr 2020
Implemented GPipe, a multi-GPU pipeline parallelism technique for large-scale model training, as a PyTorch library with CUDA, autograd, and long skip connection optimizations; later upstreamed into PyTorch as the official Pipe APIs.
Hangulize, Oct 2010 – Present
Designed a Hangul transcription algorithm and released it as a free web tool widely used by professional Korean translators.
TrueSkill, Jan 2012 – Dec 2015
Implemented TrueSkill™, the rating algorithm behind Xbox Live, as a Python library; presented at PyData Berlin 2019.
Contributions
Contributed upstream patches improving GPU safety (#27371) and API consistency (#21006, #25985) in PyTorch. Fixed subdomain URL bug (#108) in Flask.

Publications

*Contributed equally

Public Speeches


Languages

Education

Computer Software, Kwangwoon University, 2008, Completed the first year only.