I spent months inside verl (an RL post-training framework), forked it, then stopped. Wrote up the internals, the tooling a fork costs, and a nasty NCCL bug.

In three linesA researcher who spent months inside verl (ByteDance's RL post-training framework) documents its internals: RLHF loop orchestration, single-controller pattern, data structures (DataProto), and a NCCL bug discovered. Abandoned fork but knowledge shared with the community.

Summary generated by Claude — human-verified