A tweet from @kimmonismus reveals GPT-5.5 Pro shows significant Epoch benchmark gains, and the non-Pro GPT-5.5 surpasses GPT-5.4 Pro, suggesting major efficiency improvements at OpenAI. What Happened A tweet from AI researcher @kimmonismus reports two key findings about OpenAI's latest model iteration: GPT-5.5 Pro represents a significant leap in the Epoch benchmark (a suite measuring AI training efficiency, data scaling, and compute-optimal performance). GPT-5.5 (non-Pro) surpasses GPT-5.4 Pro, meaning the base model now outperforms the previous top-tier version. This suggests OpenAI has achieved substantial algorithmic improvements without requiring the full Pro-level compute budget. Context OpenAI's model numbering has historically indicated major version jumps (GPT-3 to GPT-4) with minor increments for refined variants (GPT-4 to GPT-4.5). The jump from GPT-5.4 to GPT-5.5 appears to be a significant mid-cycle improvement — especially notable because the base model now exceeds the previous Pro tier.…