Opus 5.5 had zero regressions. GPT-6 Sol had five, at 29% of the cost.

Everyone posted benchmark tables yesterday. One person replayed real merged commits.

paddo.dev took six production changes from a TypeScript monorepo of about 3,700 files, changes that had already been written, reviewed and merged by humans, and ran both models at them 20 times each through Claude Code and Codex at default medium effort. Opus 5.5: 13 of 20 clean runs, zero test regressions, $45.81 total. GPT-6 Sol: 8 of 20 clean, five regressions, $13.16. On four self-contained tasks with 4,176 assertions, both scored 100%.

That gap only appears on the messy work. Self-contained tasks are where the vendor tables live, and there both models are fine. The regressions showed up on changes that touched things the prompt didn't mention. paddo's conclusion is the one I'd give too: use Sol where tests and review are strong, use Opus 5.5 for unattended work on thin suites. A cheap model that breaks something once every four runs is only cheap if a human catches it.

The independent numbers point the same way and disagree about magnitude, which tells you something about how noisy launch-day evaluation is. Artificial Analysis puts Sol (max) at 48 on the Intelligence Index, rank 18 of 212, against 58 for Opus 5.5, and traced Sol's ~100 Elo GDPval drop from its predecessor to deliverables that skipped required parts of the task. Browser Use got the opposite result on browser agents: Sol at medium scored 66.9 to Opus 5.5's 59.4 at 3.5x less cost. Nate Herk preferred Opus on seven of eight jobs and paid $213 against $74 for it, reported by The Neuron.

The pricing story is more complicated than the headline 40% cut. Artificial Analysis measured Opus 5.5 at max effort at $5.98 per index task against $5.86 for Opus 5, via Latent Space. The per-token price dropped and token usage rose to meet it. Simon Willison watched Opus 5.5 at max burn all 128,000 output tokens reasoning about a pelican SVG. Twice. About $2.56 per failure.

Anthropic's own migration guide says medium effort matches Opus 5 at high on coding. Thinking is always on now, you can't disable it or set a budget, and forced tool_choice: any returns a 400. Keep your old high-effort setting and you'll pay for longer turns you didn't ask for. Set max_tokens to 128,000, because thinking counts against it. And change effort per-message using the beta, because changing it at the top level between requests invalidates your prompt cache.

Also flagged on the benchmark itself: ProgramBench co-author Ofir Press pointed out Anthropic ran 166 of the benchmark's 200 instances and reports average tests passed, while the official leaderboard counts only fully completed tasks. A partial solve often passes 60-70% of tests. The 91.2% in the system card isn't the same metric as the 91.2% you'd read off the leaderboard.