GPT-5.6 Sol Ultra¶

Development line: project:gpt-5-6-sol-ultra · thread gpt-5-6-sol-ultra
Last event: - · 0 dated since - · Researched: 2026-09-05 · confidence: high

What it is¶

GPT-5.6 Sol Ultra is a mode of GPT-5.6 Sol for engineers who need parallel agents.

• Four agents by default
• Tools
• Long context

The API documents model ID gpt-5.6-sol with no separate Ultra ID. Use it for heavy verifiable tasks, not for regular requests.

Development line¶

• The dated line is not written up yet. What is known stands in the sections below.

What changed¶

• 2026-07-09 — OpenAI released GPT-5.6 to general availability. Sol became the flagship tier. Ultra became a mode with multiple parallel agents.
• 2026-07-12 — A published note on the cycle double cover conjecture proof credited the proof to GPT-5.6 Sol Ultra. It credited the write-up to Codex with GPT-5.6 Sol.
• 2026-07-30 — OpenAI lowered API prices by 20% for Terra and 80% for Luna. Sol Ultra was unaffected by this change.
• 2026-08-21 — OpenAI lowered the Sol API price by more than 20% for the next three months.

How to use this¶

No verified practical-use change can be proposed from the dated links alone.

1. Specify model gpt-5.6-sol for API use. There is no separate Ultra identifier in the model catalog. — https://developers.openai.com/api/docs/models/gpt-5.6-sol
2. Select high reasoning effort for a difficult single task. The available levels are none, low, medium, high, xhigh, and max. — https://developers.openai.com/api/docs/models/gpt-5.6-sol
3. Build an ultra-like run with beta multi-agent in the Responses API for parallel work. — https://openai.com/index/gpt-5-6/
4. Choose ultra in Codex when the task justifies higher token use. The mode is available on Plus and higher tiers. — https://openai.com/index/gpt-5-6/

Best practices¶

• Do not pass gpt-5.6-sol-ultra as an API model ID. Use gpt-5.6-sol with a reasoning configuration or a multi-agent workflow. — https://developers.openai.com/api/docs/models/gpt-5.6-sol
• Evaluate ultra by final result verification. The mode increases token usage because it sums work across parallel agents. — https://openai.com/index/gpt-5-6/
• Pin a snapshot instead of relying on a model alias so behavior stays stable. — https://developers.openai.com/api/docs/models/gpt-5.6-sol

Superseded by this¶

• 2026-07-09 — Treating Ultra as a separate model is obsolete. OpenAI describes it as a mode of GPT-5.6 Sol, and the API catalog documents gpt-5.6-sol.

Still unknown¶

• The PDF document lacks a creation date, so it confirms attribution without dating it independently.
• The text of the X post was unavailable during review, so its wording and date were not used as evidence.

Sources¶

Agent brief¶

• Subject: project:gpt-5-6-sol-ultra, thread gpt-5-6-sol-ultra, 0 dated events - → -.
• Practical note: No verified practical-use change can be proposed from the dated links alone.
• Confidence: high. Dated supersedes above are the authority for what is obsolete.