GPT-6 Astra vs GPT-5.6 Luna

The widest price gap inside OpenAI's own catalog -- forty times per output token -- between the GPT-6 flagship and the tier most volume work runs on.

What the numbers say

• GPT-5.6 Luna is about 42x cheaper on output tokens (14.4 vs 600 credits per 1M).
• Both take the same 1.1M-token context window.
• GPT-6 Astra is the newer release (September 2026 vs July 2026).

Derived from the live registry Zeplik routes and bills against. Credits: 1 credit = $0.10, computed from the raw provider rate with a 1.20x margin.

Side by side

Try both on Zeplik

The honest answer to most model debates is to run your own prompt on both. Zeplik puts GPT-6 Astra and GPT-5.6 Luna in the same chat, so you can switch mid-conversation and compare answers on the work you actually do.

Frequently asked questions

What is the difference between GPT-6 Astra and GPT-5.6 Luna?

GPT-5.6 Luna is about 42x cheaper on output tokens (14.4 vs 600 credits per 1M). Both take the same 1.1M-token context window. GPT-6 Astra is the newer release (September 2026 vs July 2026).

Is GPT-6 Astra or GPT-5.6 Luna cheaper?

GPT-5.6 Luna is cheaper: 14.4 credits per million output tokens against 600. 1 credit = $0.10, computed from the raw provider rate with a 1.20x margin.

Which has the larger context window, GPT-6 Astra or GPT-5.6 Luna?

Neither: both take 1.1M tokens.

Can I use both GPT-6 Astra and GPT-5.6 Luna on Zeplik?

Yes. Zeplik is a multi-model chat, so both sit behind one account and you can switch between them mid-conversation to compare answers on your own prompt.

Do GPT-6 Astra and GPT-5.6 Luna need a paid plan?

One of the two is open to free accounts; the other needs a paid plan (Plus or above).

Related comparisons

• Claude Opus 5.5 vs GPT-6 AstraAnthropic's and OpenAI's deep-reasoning flagships, eighteen days apart -- and Astra asks two and a half times Opus 5.5's price for a window only five percent larger.
• GPT-6 Luna vs GPT-5.6 LunaThe cheapest upgrade on the board: GPT-6 Luna halves its predecessor's input price and cuts output by well over half, at the same 1,050,000-token window.
• GPT-6 Sol vs GPT-6 AstraThe upgrade decision inside the GPT-6 line: Astra costs five times Sol for the same 1,050,000-token window, so the question is which work is hard enough to need it.
• GPT-5.6 Luna vs Gemini 3.7 FlashThe value tier where volume work actually runs: OpenAI's Luna against Gemini 3.7 Flash, at a fraction of either lab's flagship price.
• GPT-6 Astra vs GPT-5.6 SolThe upgrade decision almost every OpenAI user is actually making: GPT-6 Astra costs five times Sol per token for the same 1,050,000-token window, so the question is which work is hard enough to need it.
• GPT-5.6 Luna vs Gemini 3.5 FlashThe value tier where volume work actually runs: OpenAI's Luna against Gemini Flash.