GPT-6 vs GPT-5.6: prices, specs and what changed

GPT-6 is cheaper and newer than GPT-5.6 without being bigger. OpenAI cut the list price of GPT-6 Sol and GPT-6 Luna to half of GPT-5.6 Sol and GPT-5.6 Luna's promotional prices, kept the same 1.05M-token context and 128K-token output, and moved the knowledge cutoff from February to April and May 2026. On OpenAI's own tests the GPT-6 models also make fewer mistakes and do more per task.

If you are on GPT-5.6 today, the move is mostly a change to model, plus a few request details covered below.

How much cheaper is GPT-6 than GPT-5.6?

How OpenAI's list prices changed, for prompts up to 272K input tokens:

For scale, GPT-6 Astra's rates are five times GPT-6 Sol's on every line. The live table at the end of this guide shows what each GPT-6 model costs on SeedRouter today.

The prices come from OpenAI's pricing page and the GPT-6 Sol and Luna announcement, which calls it "reducing API prices for Sol and Luna by 50% compared with their GPT‑5.6 promotional pricing". The GPT-5.6 Sol page notes that its promotional price runs at least through November 21, 2026.

There is no GPT-6 Terra. GPT-6 Sol now costs the same as GPT-5.6 Terra on input and less on output, so a Terra workload can move up to Sol without paying more per input token.

The long-context rule did not change: above 272K input tokens the whole request is billed at 2x input and 1.5x output, on both generations.

What stayed the same and what changed?

The figures are from OpenAI's model pages for GPT-5.6 Sol, GPT-6 Sol, GPT-6 Luna and GPT-6 Astra.

Is GPT-6 better than GPT-5.6?

On the results OpenAI published, yes. These are OpenAI's own numbers:

• Mistakes. On its factuality evaluation, GPT-6 Sol makes "about half as many mistakes as its predecessor", and GPT-6 Luna at higher effort matches GPT-5.6 Sol at about a hundredth of its cost.
• Business workflows. On AutomationBench, GPT-6 Luna at high effort improves on GPT-5.6 Luna by 5.4 percentage points at 58% lower cost per task.
• Coding. On FrontierCode, GPT-6 Sol "improves substantially over GPT‑5.6 Sol". In the Astra launch table, GPT-6 Astra scores 57.9% on Terminal-Bench 4.0 against 37.3% for GPT-5.6 Sol.
• Computer use. GPT-6 Luna at max effort exceeds GPT-5.6 Sol at medium effort on OSWorld 2.0 "at one tenth of its cost". GPT-6 Astra scored 72.6% in about 40 minutes per task where GPT-5.6 Sol scored 65.7% in about 75.

OpenAI also says the GPT-6 models write "slightly shorter answers overall without losing substance", with less jargon in technical conversations.

Is GPT-6 Luna cheaper than GPT-5.6 Luna?

Yes. On OpenAI's list, GPT-6 Luna's input and cached-input rates are half of GPT-5.6 Luna's, and its output rate is 42% of it, so a typical request costs less than half as much.

What should I change when moving from GPT-5.6?

OpenAI's GPT-6 migration notes list the checks:

1. Model ID. Use gpt-6-sol, gpt-6-luna or gpt-6-astra.
2. Reasoning effort. Keep your current effort where it exists. GPT-6 Astra has no none; use low. If you used minimal, start with low.
3. Sampling. Unless effort is none, remove temperature, top_p and top_logprobs (and logprobs on Chat Completions).
4. Tools. Use the Responses API for reasoning with tools. On Chat Completions, GPT-6 Sol and Luna call functions only at none effort, and GPT-6 Astra not at all.
5. Effort mid-conversation. To change effort between turns without losing the prompt cache, append a configuration_update input item instead of changing the request-level effort.

The request and response formats are otherwise the ones you already use.

Frequently asked questions

Is GPT-6 Sol better than GPT-5.6 Sol?

Yes, on OpenAI's published results: about half the factual mistakes, better coding scores, and half the token price of GPT-5.6 Sol's promotional rate.

Is GPT-6 Astra better than GPT-5.6 Sol?

Yes. GPT-6 Astra is OpenAI's most capable model and leads GPT-5.6 Sol on every coding benchmark in OpenAI's launch table, from Terminal-Bench 4.0 to DeepSWE. It also costs more: its list rates are 2.5 times GPT-5.6 Sol's promotional rates on every line.

Does GPT-6 have a bigger context window than GPT-5.6?

No. Both generations read up to 1,050,000 tokens, with 922,000 of them input, and write up to 128,000.

Can I still use GPT-5.6 on SeedRouter?

SeedRouter sells the GPT-6 models: GPT-6 Sol, GPT-6 Luna and GPT-6 Astra. GPT-5.6 is not offered.

What does GPT-6 cost on SeedRouter?

Try GPT-6 on your own prompts

Run a prompt you already send to GPT-5.6 through GPT-6 Sol or GPT-6 Luna in the browser and compare the answer and the token count. The Astra vs Sol vs Luna guide helps you pick between them.