VLLM V0 TO V1: CORRECTNESS BEFORE CORRECTIONS IN RL

Summary from the TLDR AI newsletter

The vLLM V1 update improved inference correctness by addressing discrepancies in logprob computation, runtime defaults, inflight weight updates, and final projection precision. Key fixes included adjusting processed logprobs, disabling prefix caching, matching weight update models, and ensuring fp32 lm_head computation to align with vLLM V0's behavior. These changes resolved initial training mismatches, ensuring the new engine maintains expected RL performance without unnecessary objective-side corrections.