Explain PPO and GRPO for LLM alignment. Why did GRPO drop the value model?
RL alignment moved from PPO to leaner methods, and DeepSeek-R1 made GRPO famous. The signal is knowing what the value/critic model does in PPO and how GRPO replaces it. Here is the mechanism, not the acronyms.
Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.
RL alignment moved from PPO to leaner methods, and DeepSeek-R1 made GRPO famous. The signal is knowing what the value/critic model does in PPO and how GRPO replaces it. Here is the mechanism, not the acronyms.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.