As of: 2026-11-13 13:49 CET.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/m/gpt-5-6-sol/

# GPT-5.6 Sol

OpenAI, GPT-5.6 family. Status: legacy. Type: reasoning model. Released: 2026-07-09. Training cutoff: 2026-02.

## How to call it

| Provider | Model id | Endpoint | Docs |
|---|---|---|---|
| OpenAI API | `gpt-5.6-sol` | https://api.openai.com/v1/responses | https://developers.openai.com/api/docs/models/gpt-5.6-sol |
| Azure OpenAI (Microsoft Foundry) | `gpt-5.6-sol` |  | https://learn.microsoft.com/en-us/azure/foundry/foundry-models/concepts/models-sold-directly-by-azure |
| OpenRouter | `openai/gpt-5.6-sol` |  | https://openrouter.ai/openai/gpt-5.6-sol |
| Web app |  |  | https://chatgpt.com |

## Pricing

- Input: $4 per 1M tokens
- Cached input: $0.40 per 1M tokens
- Output: $20 per 1M tokens
- Unit as published: per 1M tokens (USD), standard tier
- Note: prompts >272K input tokens billed 2x input / 1.5x output
- Source: https://developers.openai.com/api/docs/pricing
- Last checked: 2026-09-29

## Specs

- Input: text, image
- Output: text
- Context window: 1,050,000 tokens
- Max output: 128,000 tokens
- Open weights: no
- Licence: proprietary

## What it has not seen

- Published training cutoff: 2026-02 (February 2026).
- AI events after it on Post-Cutoff: 1,919 (439 major, 85 historic), as of 2026-11-13.
- Already missing at launch: 138.
- Briefings of the news since February 2026: https://postcutoff.com/briefings/cutoff-2026-02-s.md (short), https://postcutoff.com/briefings/cutoff-2026-02-m.md (medium), https://postcutoff.com/briefings/cutoff-2026-02.md (full).
- Its card, with five things it has never heard of: https://postcutoff.com/you/gpt-5-6-sol/

## What stands out

- Named-tier family: GPT-5.6 introduced the Sol/Terra/Luna tier names (flagship/balanced/fast) replacing pro/mini/nano naming. Source: https://developers.openai.com/api/docs/changelog
- Max reasoning effort: Reasoning effort none/low/medium/high/xhigh/max. Source: https://developers.openai.com/api/docs/models/gpt-5.6-sol
- Fast mode long context (found after launch): Fast mode extended to long-context requests on Aug 5 2026. Source: https://developers.openai.com/api/docs/changelog

## Notes

GPT-5.6 flagship; the gpt-5.6 alias routes here. Superseded by GPT-6 Sol/Astra but still offered. OpenRouter lists $2/$10, lower than OpenAI list price $4/$20.

Previous flagship; replacement target for deprecated gpt-5/o3 snapshots.

```bash
curl https://api.openai.com/v1/responses \
 -H "Authorization: Bearer $OPENAI_API_KEY" -H "Content-Type: application/json" \
 -d '{"model":"gpt-5.6-sol","input":"Hello"}'
```

Sources:
- https://developers.openai.com/api/docs/models/gpt-5.6-sol
- https://developers.openai.com/api/docs/pricing
- https://developers.openai.com/api/docs/changelog
- Models overview: https://developers.openai.com/api/docs/models

Model page: https://postcutoff.com/m/gpt-5-6-sol/