LLM Wire Format Benchmark: Which Format Can AI Actually Read and Write?

Every LLM wire format claims token savings. Nobody proves whether AI models can actually comprehend the format at scale, or produce valid output in it. We ran 23 comprehension evals across 10 models and 3 providers. We ran generation evals across 11 models. Deterministic ground truth. No LLM judge. Reproducible from one command. JSON breaks at 500 records. GPT-5.5 returns empty strings. It can't even attempt an answer. Opus miscounts 500 as 356 and then spends 143 lines manually enumerating sy...