GPT-5.5 is OpenAI’s first fully retrained base model since GPT-4.5 — codenamed “Spud” internally — and it scores 82.7% on Terminal-Bench 2.0, making it the leading model for autonomous terminal-based coding tasks as of April 2026. If you’re deciding whether to migrate Codex pipelines or agentic coding workflows to GPT-5.5, this guide covers benchmarks, setup, computer use, and real workflow patterns.
What Is GPT-5.5 and Why It’s a Big Deal for Developers GPT-5.5 is OpenAI’s most capable agentic model, launched April 23, 2026, to ChatGPT Plus, Pro, Business, and Enterprise subscribers. It is the first fully retrained base model since GPT-4.5 — internally codenamed “Spud” — rebuilt from the ground up for long-horizon agentic tasks rather than fine-tuned on top of GPT-5.4. Unlike incremental releases, GPT-5.5 changes the underlying model weights and reasoning patterns to prioritize terminal operations, computer use, and multi-step autonomous execution. On Terminal-Bench 2.0, it scores 82.7%, beating Claude Opus 4.7 (69.4%) by 13.3 percentage points and edging out Claude Mythos Preview (82.0%) in a near-statistical tie. On GDPval — a benchmark spanning 44 real-world occupations — it reaches 84.9%. For developers running coding agents, the practical implication is clear: GPT-5.5 handles bash-heavy autonomous workflows better than any prior model. However, on SWE-Bench Pro (real GitHub issue resolution), it scores 58.6% versus Claude Opus 4.7’s 64.3%, which means the model to choose depends heavily on whether your tasks live in the terminal or in production codebases.
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