Codex models in 2026: GPT-6 Astra, GPT-5.6 Sol, Terra, Luna, GPT-5.3-Codex, and legacy models
Updated: Sep 17
Codex in September 2026 is no longer tied to one dedicated coding model. The current stack spans GPT-6 Astra, GPT-5.6 Sol, Terra and Luna, plus GPT-5.3-Codex as a specialized agentic coding model.
Which model appears depends on whether you sign in with a ChatGPT plan, use Codex in the desktop app or CLI, or call a model directly through an API key.
··········
THE CURRENT CODEX MODEL MAP
Codex is a product surface for software-development work, not the name of one single model. Current access mixes general frontier models with a specialized Codex model depending on plan, client version, and whether billing comes from ChatGPT or an API key.
........
Model | Current Codex role | Access note |
|---|---|---|
GPT-6 Astra | Highest-end complex coding and end-to-end computer work | Available in Codex on eligible paid plans; Plus includes limited Astra usage |
GPT-5.6 Sol | Advanced professional coding and reasoning | Codex on Plus, Pro, Business, Enterprise |
GPT-5.6 Terra | Balanced intelligence and cost | Codex default option for Free/Go; also on higher plans |
GPT-5.6 Luna | Fast, low-cost coding workloads | Codex on Plus, Pro, Business, Enterprise |
GPT-5.3-Codex | Specialized agentic coding model | API and Codex-oriented workflows; 400K context |
........
··········
GPT-5.6 TERRA REPLACED GPT-5.4 FOR MANY CODEX USERS
OpenAI removed GPT-5.4 and GPT-5.4 mini from Codex for ChatGPT-account sign-in on August 31, 2026. The migration guidance is GPT-5.6 Terra for GPT-5.4 and GPT-5.6 Luna for GPT-5.4 mini. This did not remove GPT-5.4 from the OpenAI API.
··········
GPT-6 ASTRA SITS AT THE TOP OF THE CURRENT CODEX STACK
Astra is OpenAI's highest-end model for difficult end-to-end work, including software engineering and computer use. Plus includes Astra in Codex with limited usage, while higher plans receive broader allowance depending on plan and workspace rules.
··········
GPT-5.3-CODEX REMAINS A SPECIALIZED AGENTIC CODING MODEL
GPT-5.3-Codex has a 400,000-token context window, 128,000 maximum output tokens, and low through xhigh reasoning settings. OpenAI describes it as optimized for long-running agentic coding tasks and interactive steering.
··········
CHATGPT SIGN-IN AND API-KEY USE HAVE DIFFERENT BILLING
Signing in to Codex with a ChatGPT account consumes the plan's Codex allowance and any applicable credits. Supplying an API key instead uses normal OpenAI API pricing. A ChatGPT subscription does not automatically include API token spend.
··········
OLD CODEX MODEL NAMES SHOULD BE TREATED AS LIFECYCLE REFERENCES
GPT-5.1-Codex and GPT-5.2-Codex are useful for understanding earlier coding generations, but a 2026 workflow should not assume they represent the current Codex default. Migration decisions should start from the current model list rather than the historical article title.
··········
HOW TO CHOOSE A CODEX MODEL IN 2026
Use Terra for balanced everyday agentic coding, Luna when speed and cost dominate, Sol for harder professional engineering, Astra for the hardest end-to-end tasks, and GPT-5.3-Codex when its specialized agentic-coding behavior or compatibility is specifically useful.
··········
FOLLOW US FOR MORE
··········
DATA STUDIOS
··········
