Senior Machine Learning Engineer (Fulfilment)

About the role

Grab is looking for a Senior Principal Data Scientist 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
• Fine-tune open-source large language models on domain data to predict, explain and simulate user decisions, covering supervised fine-tuning, preference-based alignment and iterative improvement
• Integrate RL and LLM systems into real-time production environments serving millions of users, working with data and backend engineers

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
• Experience fine-tuning large language models in production, including at least one preference-based alignment method (RLHF, DPO or GRPO)
• 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 with LoRA, QLoRA or PEFT, and evaluation metrics for generative models
• Distributed training frameworks such as DeepSpeed, FSDP or 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