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Hai Tang

@haitang

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AI/ML Engineer at OpenAI building post-training pipelines for GPT-4.5, GPT-4.1, and GPT-4o.

United States

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At OpenAI, I built and led core components of the post-training pipeline used to train GPT-4.5, GPT-4.1, and GPT-4o. I designed an RL framework for LLM post-training, including training-loop components and rollout generation.

I also built modeling infrastructure behind Advanced Voice Mode, working across the audio encoder and decoder pipeline for real-time speech. My work supported multimodal development for GPT-4o and GPT-4o-mini, as well as training infrastructure for GPT-4 Turbo.

At Google, I led large-scale model inference and built production serving infrastructure for Vertex AI, powering ML features in Gmail and Google Docs. I also contributed to T5X, PaxML, Orbax, and TensorFlow DTensor, including foundational distributed training capabilities.

Experience

Work history, roles, and key accomplishments

Current

Member of Technical Staff

Current

OpenAI

Sep 2023 - Present (3 years)

Built and led core components of the post-training pipeline for GPT-4.5, GPT-4.1, and GPT-4o, including RL-based optimization, rollout generation, and large-scale distributed training. Designed an RL framework for LLM post-training and managed checkpointing/recovery strategies for large-scale runs.

LLM Training LLM Post Training RLHF Loops Rollout Generation Checkpointing Distributed Training Model Evaluation Multimodal ML Encoder Python Jax PyTorch TensorFlow

Staff Software Engineer

Google

Jun 2016 - Sep 2023 (7 years 3 months)

Led large-scale online/offline inference for large models and built production model-serving infrastructure for Vertex AI. Contributed to JAX-TensorFlow interoperability and open-source frameworks T5X, PaxML, and Orbax, and prototyped TensorFlow DTensor capabilities.

ML Inference Model Serving Vertex AI Jax TensorFlow T5 Transformer PaxML Orbax DTensor Distributed Training RPC Microservices Python C++

Student System Administrator & Engineer

Johns Hopkins University

Sep 2014 - May 2016 (1 year 8 months)

Designed and operated the IDIES database and web services, deployed sensor infrastructure for temperature telemetry, and helped administer over 1,000 servers and workstations across a heterogeneous fleet.

Database Administration Web Services Sensor Infrastructure System Administration Heterogeneous OS Architecture

Systems Engineer

NS Solutions Co. Ltd.

Jul 2011 - Jul 2014 (3 years)

Designed enterprise Java/J2EE applications and built ETL pipelines into an Oracle data warehouse integrating operations across India, Brazil, and Japan. Optimized business workflows.

Java J2EE ETL Oracle Data Warehouse Business workflows