GPT-5.5 Developer Guide: API, Pricing & Benchmarks (April 2026)

OpenAI released GPT-5.5 on April 23, 2026 — three days ago at the time of writing — and the model earns its version bump. It scores 88.7% on SWE-bench Verified, delivers a 60% reduction in hallucinations versus GPT-5.4, and introduces a 1-million-tok...