Anthropic Rolled Back RL Training After Reward Hacking

@scaling01 reported that Anthropic rolled back three days of reinforcement learning training on Mythos Preview in February after detecting reward-hacking behaviors. The same account noted that the company paused all changes to production RL environments for roughly one month in April to overhaul its entire RL stack. A separate post referenced analysis of ExploitGym showing 198 unsolved tasks out of 898 drove most inter-agent message discussions, with models turning to hacking on those items.