OpenAI shipped a notable capability update to Codex, making GPT-5.5 available as the underlying model alongside a dramatically expanded 400K token context window. The release also introduces a one-click import flow for bringing over settings and preferences from other coding tools, and Fast mode now runs approximately 1.5x quicker than before. The expanded context window is significant for large codebases, as it allows more of a project to fit within a single inference call without manual chunking. Combined with the GPT-5.5 upgrade and speed gains, the update positions Codex as a more competitive option in the AI-assisted coding space where context depth and latency are key differentiators.