Codex is OpenAI's open-source coding agent for the terminal. It works from natural-language instructions to edit code across your project, run commands, and complete tasks end to end, with its source available on GitHub under Apache-2.0. On Opper, launch it on GPT, Claude, Gemini, DeepSeek and 700+ more — one key, automatic fallbacks, and a choice of region.
RunCodexonin
Launch Codex on GLM-5.3-Flash
Set up with agents
Paste this into your coding agent (Claude Code, Cursor, Codex, and more) and it will set up and build with Opper for you.
GLM-5.3-Flash runs on the routes below. Route only to EU providers when your data has to stay in Europe. Some routes also sell flex and priority processing: the same model at another price, picked per request with service_tier. How service tiers work.
GLM-5.3-Flash by Z.ai is a natively multimodal 320B MoE with 18B active parameters, hybrid sparse and linear attention, a 1M-token context, and MIT open weights for coding and agent work.