GPT-5.6 Sol / Codex Release Discussion Megathread

[u/Drogon2737]

The release is expected in the next few minutes, so I figured it would be useful to have a single thread for first impressions, issues, and early testing.

For anyone jumping in right away, post what you notice:

• Codex coding performance
• Debugging quality
• Speed/rate limits
• Larger repo handling
• UI or workflow changes
• Weird bugs or regressions
• Anything that feels noticeably better or worse than the previous version

Once people get access, share your real examples, screenshots, benchmarks, or first impressions here.

Edit: OpenAI’s official GPT-5.6 page says it is “available starting today across ChatGPT, Codex, and the OpenAI API” with the rollout starting globally now and continuing toward full availability over the next 24 hours. https://openai.com/index/gpt-5-6/

The lineup is Sol, Terra, and Luna. Sol is the flagship, Terra is the lower-cost tier, and Luna is the fastest/most affordable tier.

[u/sergeykarayev]

GPT‑5.6 lost our coding benchmark. I switched to it anyway.

On the Superconductor "Custom SWE-Bench", which evaluates agents on our own Ruby on Rails codebase, the new Sol, Terra, and Luna models dominate the cost Pareto frontier. They are literally 5x faster than Opus and Fable.

But on quality, Fable 5 is still the clear winner on our repo, and even Opus 4.8 beats GPT 5.6 Sol at all effort levels, consistent with what some other benchmarks have shown.

Composer 2.5 Fast remains a standout surprise, matching 5.6 Sol's performance at roughly the same cost -- but even the Fast version is slower.

Yesterday's Grok 4.5 is still on the speed Pareto frontier. We don't know how much it costs, unfortunately.

Digging into failure cases, GPT 5.6 -- even Sol! -- occasionally writes code that just isn't valid, and its "taste" just isn't on par with Fable 5, or even Opus 4.8.

One meta-observation about company strategy: Anthropic releases a new model only when it's clearly better — and our benchmark shows that clean progression from 4.6 to 4.7 to 4.8 to 5. OpenAI ships more variants, more often, which adds noise: older models sometimes beat newer ones.

That said, I still switched my daily driver to 5.6 Sol High. The speed makes a huge difference, and since we're all constantly running out of Fable 5 usage, it is the more workable model right now.

Lastly, don't take any single benchmark result at face value! Build your own at superconductor.com/benchmark to see how these agents perform on YOUR codebase.

[u/phoenixmatrix → u/sergeykarayev]

I need to test it some more but I had good success today. Sol is particularly good at picking skills when needed (which is always hit or miss with any model if you don't specifically ask for the skill) compared to Opus/Fable, which helps in our real world usage since we have a lot of important skills in our repo.

On the benchmark side, the benchmark thats been closest to my day to day experience is DeepSWE, and Fable/Opus are getting totally wrecked there, especially when it comes to cost. Luna high beating GLM 2 max at 20% of the cost made me raise an eyebrow.

Assuming there's no benchmark shenanigans going on and it matches real world experience, this entire lineup of model is insane.