Claude agents spent 30 hours "playing" on a virtual island and learned without rewards

MIT CSAIL researchers left copies of Claude Opus 4.7, nicknamed Eko, alone on a Roblox-like virtual island for 30 hours with no tasks. The agents set their own goals, built shapes and invented games, and later outperformed fresh agents on test tasks.

• Eko agents spent 30 hours on a virtual island with no external tasks or rewards
• Eko built hearts, pyramids, its own name and the Cassiopeia constellation from blocks
• Agents that had "played" performed better on later tests than fresh copies
• Deleting lines from the agents' memory files degraded their performance