GPT-5.6 Luna vs Terra vs Sol vs Sol Pro: roles, context, reasoning, pricing, and access

GPT-5.6 is a four-name family in practical use: Luna, Terra, Sol, and Sol Pro. Luna, Terra, and Sol are public API base models; Sol Pro is the Pro-class ChatGPT option for the most difficult work.

Luna, Terra, and Sol all list a 1.05-million-token context window and 128,000 maximum output tokens, but their cost and workload positioning differ sharply.

··········

THE GPT-5.6 FAMILY HAS THREE PUBLIC API BASE MODELS

Luna, Terra, and Sol are explicit API models. Sol Pro is described separately as the highest-capability GPT-5.6 option inside ChatGPT for difficult tasks and longer-running workflows.

........

Model	Role	Context / max output	API pricing per 1M tokens
GPT-5.6 Luna	High-volume, cost-sensitive	1.05M / 128K	$0.20 input / $1.20 output
GPT-5.6 Terra	Balanced capability and cost	1.05M / 128K	$2 input / $12 output
GPT-5.6 Sol	Flagship professional model	1.05M / 128K	$4 input / $20 output
GPT-5.6 Sol Pro	ChatGPT Pro-class reasoning	Product-specific	Not listed as a separate public base-model API row

........

··········

LUNA IS THE LOW-COST END OF THE FAMILY

Luna is optimized for high-volume workloads and is the standard ChatGPT default for Free and Go. It also powers their Think option rather than switching them to Sol.

··········

TERRA IS THE BALANCED MIDDLE TIER

Terra is positioned between Luna and Sol for workloads that need stronger capability without flagship pricing. It is available through the API and selected Work or Codex surfaces rather than the ordinary standard-chat picker.

··········

SOL IS THE FLAGSHIP GPT-5.6 MODEL

Sol is designed for complex professional work. The API alias gpt-5.6 currently routes to GPT-5.6 Sol, while eligible paid ChatGPT plans use Sol across Instant and the available higher thinking levels.

··········

SOL PRO IS A DIFFERENT PRODUCT POSITION

Sol Pro is the Pro-class option for the hardest GPT-5.6 tasks. It should not be presented as if it were simply another public base-model API row alongside Luna, Terra, and Sol.

··········

DS CALCULATION: PRICE SPREAD INSIDE ONE MODEL FAMILY

At current list prices, Sol input is 20× Luna input and Sol output is about 16.7× Luna output. Terra sits at 10× Luna on both input and output. Equal context windows therefore do not imply equal economics.

··········

THE PRODUCT SURFACE CHANGES WHICH FAMILY MEMBERS YOU CAN SEE

Standard Chat primarily exposes Luna or Sol depending on plan. Work and Codex can expose broader combinations, while the API exposes all three base models directly.

··········

CHOOSING LUNA, TERRA, SOL, OR PRO

Use Luna when throughput and cost dominate, Terra for a balanced capability-cost profile, Sol for demanding professional reasoning, and a Pro-class option when the task justifies the highest reasoning path and the relevant usage allowance.

··········

FOLLOW US FOR MORE

··········

DATA STUDIOS

··········

datastudios.org