30 well-chosen training environments beat all 200

Researchers selected 30 training environments from a pool of 200 and beat the full set's relative training gain, per a Chinese Academy of Sciences paper. For teams training agents, that's a case against defaulting to more environments. The ability-aware selection method delivered a 95.6% relative gain, versus 43.4% for training on all 200.

Stack a Hierarchical Difficulty Curriculum on top of that selection, sequencing tasks by difficulty instead of feeding them in randomly. The average relative improvement reaches 143.2%, per the paper.

Not every environment type transfers the same way. Multimodal environments showed far stronger negative transfer than text-symbolic ones: a 10.7% drop against a 1.3% drop. A mismatched environment can actively hurt performance, not just fail to help.

The selection method also depends on something the paper calls conflict control. Strip it out and out-of-distribution gains collapsed from 40.3% to 2.8%. The description doesn't spell out what conflict control does mechanically, only that removing it erases most of the effect.