GPT-5.5 is the OpenAI model released on April 26, 2026 with selectable reasoning effort, of which xhigh is the highest setting, posting 39.6% on FrontierMath Tier 4, 84.9% on GDPval and 82.7% on Terminal-Bench 2.0 at launch. In this corpus it is the model that topped KernelBench at 6.57% for writing the GPU kernels it runs on and that more than doubled GPT-5.4 on fresh olympiad problems in the same issue; a week after it shipped, Codex overtook Claude Code in downloads, and in May a meta-evaluation mapped it to an implied IQ of 136.
AISystem
GPT-5.5
OpenAI's frontier model of spring 2026, whose xhigh reasoning setting topped KernelBench for GPU-kernel writing and which more than doubled its predecessor on fresh olympiad problems.
Sources
Attribution and reporting linked by this record; links do not imply independent verification.
- Welcome to April 29, 2026 (theinnermostloop.substack.com)
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