OpenAI May 2026: GPT-5.5 Instant, Codex Goals, GPT-5.6
GPT-5.5 Instant replaced GPT-5.3 as ChatGPT's default, Codex shipped Goal Mode and richer MCP, and a GPT-5.6 entry briefly surfaced in OpenAI's Codex logs. Here is the complete May 2026 OpenAI changelog and what it means for developers.