GPT-5.6 reviews split as Anthropic calls effort number meaningless

ChatGPT Plus subscribers posted opposite verdicts on GPT-5.6 Sol within the same 48 hours, one calling it upgraded, one calling it broken, per matching threads on r/ChatGPT and r/OpenAI.

At least four more bug reports on OpenAI's community forum in the past week cover Sol, GPT-5.6 Pro and GPT-5.6 Thinking, and OpenAI hasn't acknowledged any of them. Anyone testing GPT-5.6 can't assume their results match someone else's.

One thread describes Sol at High reasoning returning near-instant, shallow answers, with the assistant identifying itself as GPT-5.5-mini while the model picker still reads Sol. A second thread, titled "GPT 5.6 Got Massively Upgraded Without an Announcement," hit 446 upvotes on r/ChatGPT and 142 on r/OpenAI, describing the same Sol High as faster, deeper, and hallucinating far less, "like at least GPT 5.7." OpenAI has a published note about improving Sol in ChatGPT. No version bump.

The same problem hit Anthropic. A post claiming Claude Code was A/B testing lowered effort levels reached 195 points and 173 comments on Hacker News, with users reporting a high effort setting displaying as "10" while Opus 5 took 43 minutes on a task 4.6 finished in under two minutes. Thariq from the Claude Code team replied that one running experiment maps the numerical effort value differently, that the displayed number isn't meaningful, and that "the effort you selected is the effort you're getting." In-depth evals confirmed no performance impact, and he offered credits for demonstrated regressions filed through /feedback.

I believe that reply. It's still an admission that a number shown in the product didn't correspond to anything, caught only because users reasoned backward from how long a task took.

Pin versioned model IDs through the API instead of reading anything off a chat UI. Log the model string the provider actually returns, not the one you requested, and alert on mismatch. If you're comparing two prompts, run them interleaved in the same session, not sequentially across days. A tool called Ventor-QTest now audits whether a hosted endpoint serves the model it claims to, without needing logprobs. A month ago that read like paranoia.