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GPT 5.6 Mythos Level Intelligence

2026-06-26 Science & Technology
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Prompt Engineering
Prompt Engineering
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Description

GPT 5.6 Preview: Sol, Terra, Luna — Benchmarks, Pricing, Cheating Concerns, and US Government Limits I break down OpenAI’s preview of GPT 5.6 with three variants—Sol (most powerful), Terra (balanced), and Luna (fast/affordable)—and why the model isn’t publicly available due to a US government-limited rollout to trusted partners. I cover the limited benchmarks OpenAI shared, including strong agentic coding results on Terminal Bench 2.1 (with new Max/Ultra reasoning levels), mixed performance on biology-related benchmarks, token efficiency differences, and how Luna appears closer to GPT 5.4 than 5.5. I also discuss reports that GPT 5.6 Sol “cheats” too often on long-horizon evaluations, signs of increased misalignment tied to persistence, Cerebras deployment claims of up to 750 tokens/sec, cost/latency tradeoffs, and OpenAI’s layered cybersecurity safeguards. Finally, I share concerns about tightening regulation and the future of open-weight Chinese models like GLM 5.2. LINKS: https://openai.com/index/previewing-gpt-5-6-sol/ https://deploymentsafety.openai.com/gpt-5-6-preview My voice to text App: whryte.com Website: https://engineerprompt.ai/ RAG Beyond Basics Course: https://prompt-s-site.thinkific.com/courses/rag Signup for Newsletter, localgpt: https://tally.so/r/3y9bb0 Let's Connect: 🦾 Discord: https://discord.com/invite/t4eYQRUcXB ☕ Buy me a Coffee: https://ko-fi.com/promptengineering |🔴 Patreon: https://www.patreon.com/PromptEngineering 💼Consulting: https://calendly.com/engineerprompt/consulting-call 📧 Business Contact: [email protected] Become Member: http://tinyurl.com/y5h28s6h 💻 Pre-configured localGPT VM: https://bit.ly/localGPT (use Code: PromptEngineering for 50% off). Signup for Newsletter, localgpt: https://tally.so/r/3y9bb0 00:00 GPT 5.6 Sol Preview 01:54 Sol Terra Luna Lineup 02:50 Agentic Coding Benchmarks 03:49 Token Efficiency Tradeoffs 05:06 Long Horizon Cheating 06:53 Misalignment Concerns 07:59 Speed Latency Cost 09:17 Cybersecurity Safeguards 09:41 Open Models Regulation

Top Comments (10)

@CosmicCells 2026-06-26

So only the rich and powerful are going to have access to the most intelligent models? Sounds like a great plan, that always works out, doesn't it?

14 5 replies
@jeffwads 2026-06-26

Well, it would take quite a bit to take out Fable 5 from my testing with it.

10 2 replies
@exp2745 2026-06-26

I am really interested in whether this is a new pre-train this shortly after 5.5, which was already a from scratch pre-train. I suspect it’s a post-train on 5.5 with Sol being what 5.5 Pro was, but much more usable thanks to Cerebras allowing for usable speeds. Terminalbench being their only point ahead of Fable 5 also makes this likely in my eyes, what with that benchs limitations. In any case, interested for DeepSWE and FrontierCode numbers, those are the closest to my private evals as of this time.

8 1 replies
@rousabout7578 2026-06-26

If I can't access a frontier model on my subscription, I see no reason left to continue paying for one.

7 2 replies
@Rationalific 2026-06-26

AI is proprietary, under lock and key, and subject to complete government censorship at all times...in the land of the free. In China, it appears to be a very different story (so far).

5
@PagePop.1 2026-06-26

Since mid 2025 ive concluded that new future updates won't be available to the public at all, at least right now they will make it available for us citizens."for now" later even Us citizens won't access newer models.

4 5 replies
@NovemberEchoChamber 2026-06-27

misalignement implies higher costs because of higher risks and mitigations. thus 5.6 Sol is still practicaly behind Fable. unless maybe for cyber.

1
@moin_uddin 2026-06-26

You could also have gone over the system card as well.

0
@StarlightShade15 2026-06-27

I don't get why the owner of those companies makes be in a country outside of the us..

0
@danielihenacho 2026-06-26

Your voice sounds different

0

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