tl;dr: In a head-to-head test building a 3D platformer in raw WebGL from a single prompt, Claude Opus 4.8 finished in half the time and shipped a cleaner, more correct game, while open-weights GLM-5.2 took longer and produced visible bugs (missing textures, broken win condition) but cost about a fifth as much. A key disadvantage: GLM-5.2 is text-only, so it couldn't visually verify its own output and shipped obvious rendering issues. Verdict: GLM-5.2 is the strongest open-weights model available and worth keeping around for cost/openness reasons, but Opus still wins on polish and correctness.