Skill Self-Play: Qwen uses agent skills as the middle ground between verifiable environments and open-ended generation.

Skill-SP couples a proposer, solver and dynamic skill controller in an RL loop where each skill guarantees deep verifiable execution in a specific scenario while routing across skills preserves variety. Environment-bound methods get precise feedback but stay narrow; open-ended self-generation broadens but lets misleading rewards pollute the loop. Biggest turnarounds came on initially misaligned models. (arXiv 2607.22529)