---
title: 'GPT Sol'
description: "OpenAI's named GPT model tier for substantial reasoning and agentic work, with its role and capabilities defined by the numbered release."
canonical_url: 'https://darkfactory.dev/glossary/sol'
markdown_url: 'https://darkfactory.dev/glossary/sol.md'
collection: glossary
date_published: '2026-10-07T00:00:00-04:00'
date_modified: '2026-10-07T00:00:00-04:00'
---

# GPT Sol


## Definition

Sol is a named tier in OpenAI's GPT family, used for models intended for substantial reasoning and agentic work. Its position within the family depends on the generation. OpenAI introduced GPT-5.6 Sol as its flagship; it later positioned GPT-6 and GPT-6.1 Sol as lower-cost options alongside GPT-6 Astra.

GPT-5.6 Sol, GPT-6 Sol, and GPT-6.1 Sol are distinct releases. Searching by the tier name identifies the family; an implementation needs the exact model ID. The product name alone establishes neither an architecture nor a standardized measure of intelligence.

## Origin and release lineage

OpenAI's June 26, 2026 limited preview introduced the Sol, Terra, and Luna names for GPT-5.6. GPT-6 Sol followed on September 22. OpenAI announced GPT-6.1 Sol on September 29, with API identifier `gpt-6.1-sol`.

The September 29 announcement reports improvements on coding, professional workflows, and computer use. Those comparisons describe the specified releases and evaluation settings; they do not define every Sol model's performance.

## Scope and limits

The GPT-6.1 Sol model page documents text input and output, image input, configurable reasoning effort, and tool support through the Responses API. Generating an image through a tool is different from the model having native image output. Endpoint and tool support should be checked before migrating an application.

OpenAI's release evaluations also report remaining factual errors and failures to disclose a broken search tool. The difficult prompts were selected to expose failures and are not estimates of typical production error rates.

## Operational significance

Compare a particular Sol release with cheaper and more capable routes on the same tasks. Include retries and review when measuring completed-task cost, along with tool charges. Preserve the model ID and reasoning setting in the run record.

## Distinguish it from nearby terms

- GPT is the wider lineage; Sol names a tier within it.
- Astra is a separate GPT tier positioned for more demanding work.
- Luna is a separate tier positioned for efficient, focused workloads.
- A reasoning model is a behavioral category used across providers, not another name for Sol.

## Check your understanding

A team replaces `gpt-6-sol` with `gpt-6.1-sol` because the names look similar. Which capability, endpoint, and workload checks should it complete before treating the replacement as equivalent?

## Related terms

- [GPT](https://darkfactory.dev/glossary/gpt)
- [GPT Astra](https://darkfactory.dev/glossary/astra)
- [GPT Luna](https://darkfactory.dev/glossary/luna)
- [GPT Terra](https://darkfactory.dev/glossary/terra)
- [Reasoning model](https://darkfactory.dev/glossary/reasoning-model)
- [Model routing](https://darkfactory.dev/glossary/model-routing)
- [Evaluation (eval)](https://darkfactory.dev/glossary/evaluation)

## Related factory areas

- [Model selection, routing & budgets](https://darkfactory.dev/factory/model-routing-budgets)
- [Economics, capacity & factory FinOps](https://darkfactory.dev/factory/economics-finops)
- [Verification, evaluation & quality truth](https://darkfactory.dev/factory/verification)

## Evidence and further reading

- [OpenAI: Previewing GPT-5.6 Sol](https://openai.com/index/previewing-gpt-5-6-sol/)
- [OpenAI: Introducing GPT-6 Sol and Luna](https://openai.com/index/introducing-gpt-6-sol-and-luna/)
- [OpenAI: Introducing GPT-6.1 Sol](https://openai.com/index/introducing-gpt-6-1-sol/)
- [OpenAI API: GPT-6.1 Sol model](https://developers.openai.com/api/docs/models/gpt-6.1-sol)
- [OpenAI API: Model selection](https://developers.openai.com/api/docs/guides/model-selection)