Senior Principal Machine Learning Engineer (Fulfilment)

About the role

Grab is looking for a Senior Principal Machine Learning Engineer to lead its shift toward automated marketplace optimization. The role sits at the intersection of reinforcement learning, large language models and production systems handling hundreds of millions of requests per day, and reports to the Head of Data Science from the One-North Singapore office.

Key responsibilities

• Develop RL systems that jointly optimize pricing, dispatching and supply repositioning, with decision agents that adapt to changing conditions
• Build latent world models and marketplace state representations capturing supply-demand interactions, location patterns and user/driver behaviour
• Create policy evaluation frameworks and monitoring systems for safe deployment of new decision policies in production
• Architect LLM-based behavioural intelligence systems that predict, explain and simulate user decisions at scale
• Fine-tune open-source language models and design training strategies including supervised fine-tuning, preference-based alignment and iterative improvement
• Work with data and backend engineers to integrate RL and LLM systems into real-time production environments

Required profile

• PhD in Computer Science, Operations Research, Applied Mathematics or a related field, with at least 10 years of experience
• Experience building production ML/RL systems with online learning or simulation-based optimization
• Ability to turn ambiguous business problems into concrete modelling tasks

Required skills

• RL fundamentals: Markov Decision Processes, stochastic control, reward design
• World models and sequential modelling (RNNs, transformers, state-space models)
• LLM fine-tuning (supervised fine-tuning, RLHF, DPO, GRPO) and parameter-efficient methods (LoRA, QLoRA, PEFT)
• Evaluation frameworks for generative models
• Distributed training frameworks (DeepSpeed, FSDP, Megatron-LM)
• Python and PyTorch or TensorFlow; scalable platforms such as Spark or Ray

What we offer

• Term life insurance and comprehensive medical insurance
• Parental and birthday leave, plus volunteering leave
• A confidential assistance programme
• FlexWork arrangements such as differentiated hours