Head to head · October 2026

GPT-5.6 Terra vs GPT-5.6 Luna API pricing

GPT-5.6 Luna costs 10.0 times less per token at an 80/20 mix. Input costs 9.9x more on GPT-5.6 Terra. Output costs 10.0x more on GPT-5.6 Terra.

OpenAI

GPT-5.6 Terra

General assistants, balanced cost and quality.

Vendor: OpenAI
Type: Frontier
SayGM in / out: $1.49 / $8.94
OpenRouter in / out: $2.11 / $12.66
Blended, 80/20: $2.980
Per 100M tokens: $298
Output share of bill: 60%
SayGM vs OpenRouter: 29% lower

OpenAI

GPT-5.6 Luna

Chat products, summarisation, cheap tool calls.

Vendor: OpenAI
Type: Frontier
SayGM in / out: $0.15 / $0.89
OpenRouter in / out: $0.21 / $1.27
Blended, 80/20: $0.298
Per 100M tokens: $30
Output share of bill: 60%
SayGM vs OpenRouter: 29% lower

§ 01

Monthly bill at three usage levels

Both models on SayGM. The bars show how the price ratio turns into dollars as volume grows.

Fig. 1Monthly bill at three usage levels

GPT-5.6 Terra on SayGM
GPT-5.6 Luna on SayGM

Side project5M in · 1M out

$16

$1.64

Production app50M in · 15M out

$209

$21

High volume500M in · 100M out

$1,639

$164

Show data as a table

	GPT-5.6 Terra on SayGM	GPT-5.6 Luna on SayGM
Side project (5M in · 1M out)	$16	$1.64
Production app (50M in · 15M out)	$209	$21
High volume (500M in · 100M out)	$1,639	$164

Usage is millions of input and output tokens per month. No caching discount applied. Source: published rate cards, October 2026 snapshot. Current prices on saygm.com.

§ 02

Verdict

A common pattern is to send routine requests to GPT-5.6 Luna and escalate to GPT-5.6 Terra on failure or low confidence. On one key, that is a model name change per request rather than a second provider account.

§ 03

Per-token prices

OpenRouter figures include its 5.5% top-up fee.

USD per million tokens, input and output. OpenRouter includes its 5.5% top-up fee. Snapshot from October 2026.
Model	SayGMin / out	OpenRouterin / out, fee incl.	SayGM vs OpenRouter80/20 blend
GPT-5.6 TerraOpenAI	$1.49 / $8.94	$2.11 / $12.66	29% lower
GPT-5.6 LunaOpenAI	$0.15 / $0.89	$0.21 / $1.27	29% lower

Current SayGM rates

§ 04

GPT-5.6 Terra vs GPT-5.6 Luna questions

Which is cheaper, GPT-5.6 Terra or GPT-5.6 Luna?

GPT-5.6 Luna is about 10.0 times cheaper than GPT-5.6 Terra at an 80/20 input to output mix on SayGM, as of October 2026.

How much do GPT-5.6 Terra and GPT-5.6 Luna cost on OpenRouter?

Including the 5.5 percent top-up fee, GPT-5.6 Terra costs $2.11 input and $13 output per million tokens, and GPT-5.6 Luna costs $0.21 and $1.27.

Can I use GPT-5.6 Terra and GPT-5.6 Luna with one API key?

Yes. SayGM serves both through their native APIs on a single key, so simple tasks can go to GPT-5.6 Luna and hard ones to GPT-5.6 Terra, or both can run in a cascade model.

§ 05