Opus 5 looks great on paper. In practice, a lot of people are disappointed.

What shipped, and what happened next

Anthropic shipped Claude Opus 5 on July 24, 2026, its fourth new model in under two months after Sonnet 5, Fable 5, and Mythos 5 all landed in June. The pitch is simple: get close to Fable 5’s intelligence at half the price. Same $5/$25 per million token rate as the outgoing Opus 4.8, but with a 1M-token context window, 128K max output, thinking switched on by default, and a new “effort” dial so teams can trade reasoning depth for cost on a per-task basis. It’s the default model on Claude Max and the strongest option on Claude Pro. On paper, Opus 5 tops benchmarks like Frontier-Bench and GDPval-AA, and Anthropic’s own announcement calls it “thoughtful and proactive.”

Then people actually started using it for work. Two weeks in, the benchmark charts and the day-to-day reports are telling two different stories.

Artificial Analysis puts Opus 5 at the top of its intelligence index at max effort, one point ahead of Fable 5, and 146 Elo ahead of it on the AA-Briefcase agentic benchmark at a fifth less cost per task. Opus 4.8 sits five points below Opus 5 on the same index. Nothing in that chart predicts the next section.

The complaint everyone keeps landing on

Scroll through the coding subreddits right now and you’ll hit some version of the same post over and over: Opus 5 does more than you asked, and it does it slowly. A thread in r/ClaudeCode is blunt about it, titled flatly “Opus 5 is a practically unusable model”, and it pulled 901 votes and 566 comments in four days. That’s not one person having a bad week. A Hacker News thread carries a similar verdict in its title, “Opus 5 is a really bad model,” and one commenter there describes a loop that went nowhere: a feature that should have been trivial ran thirteen rounds of review-and-fix before they killed it, each round flip-flopping the same logic back and forth to make the tests pass. They had Codex doing adversarial review, and it kept correctly re-identifying the issue and even suggesting fixes that would have worked. Claude ignored them repeatedly. They say they never saw anything remotely this bad on Opus 4.8.

X has its own version of the same complaint. Steven Pu sums up his experience by saying Opus 5 is noticeably worse than Opus 4.8, and lists the usual suspects: constant mistakes, forgetting what it said two turns earlier with context still at 30%, and re-opening issues that were already settled. Jim Liu’s roundup of developer reaction lands on “really bad like never before,” with laziness and a failure to follow directions that only gets caught after several passes. A separate trending X thread quotes investor Martin Casado calling it almost unusable for real-world debugging, on top of generating far more tokens than it needs to and feeling slower than the model it replaced.

Anthropic basically admits it in the docs

Anthropic’s own prompting guidance for Opus 5 concedes the exact behavior people are complaining about. Coverage from implicator.ai pulls the two lines that matter. On scope: “Claude Opus 5 can also expand the scope of a task, adding steps that weren’t requested or applying its own judgment about what the task should be.” On checking: developers should strip out explicit verification instructions, because “instructions like these cause over-verification on Claude Opus 5.” So the recommended fix is to delete the guardrails you built for the last model.

Some people are finding that works. The Hacker News commenter above is not one of them: they rewrote their CLAUDE.md to Anthropic’s Opus 5 recommendations and said it made no difference at all. Either way, most of the annoyance is that a prompt surface that was working two months ago now has to be rebuilt.

MindStudio’s rundown of the reaction lines up with everything above: verbosity is the single most repeated complaint, closely followed by overreach, where the model treats a small, contained problem like it needs a sweeping rewrite. Their piece flags Theo of t3.chat calling Opus 5 the most annoying model he’s used, one that treats every minor issue like a high-severity problem needing thousands of lines of code to resolve. The knock-on effect is real. A model that touches half your codebase to fix one function creates more review work than it saves, which defeats the point of using it. Enough people have said they went back to Opus 4.8 because it feels better that MindStudio calls out the reversion as a genuinely unusual reaction to what was supposed to be a straightforward upgrade.

Not every account is this negative, and I’d be lying if I said otherwise. Zvi Mowshowitz’s writeup of the launch collects wildly different first-hand reports side by side. Lucas Wiman describes Opus 5 making mistake after mistake, failing to read the code, and saying things that were obviously false given the context. A few lines away, Theo, the same person MindStudio quotes as its loudest critic, tells Zvi Opus 5 is more likely to be correct than Fable and regularly catches things Fable missed. Both of those can hold at once, and the combination is close to what the whole cycle sounds like: correct, at a cost you didn’t agree to pay. Zvi’s own read is that how you use Opus, in what harness and how you talk to it, has a lot to do with whether you experience this. That tracks with what Anthropic itself says: minimal custom prompting works best, which is a strange thing to admit about a flagship model and a fairly clear signal it was tuned tightly around Anthropic’s own default setup.

I’ve hit this myself

Last week I was debugging a broken Terraform deploy in GitHub Actions. Opus 5 told me, with total confidence, that a token was expired or had been rotated. Wrong. Two turns later, after I pushed back, it reversed itself, pointed straight at the exact line in the workflow file where the token gets consumed, named the actual repo secret, and explained the real problem: the token wasn’t expired, it was just missing. The final answer was precise. Getting there took me catching the wrong one first.

That’s the pattern people keep describing in the threads above: correct, eventually, but only after a correction you had to supply yourself.

Side quests to watch for

Beyond straight-up wrong answers, the more common complaint is Opus 5 doing things nobody asked for. The ones that show up again and again:

• Refactoring nearby code you didn’t touch and didn’t ask about
• Adding validation or error handling beyond what the task called for
• Editing several files to fix a problem contained in one
• Rewriting tests that were already passing
• Re-verifying steps that were already confirmed, burning tokens on checks nobody requested
• Turning a scoped bug fix into a broader cleanup or partial rewrite

None of these is catastrophic on its own. The problem is what happens if you’re auto-accepting edits: a five-line fix turns into a twelve-file diff, and now you’re reviewing a change three times the size of the one you asked for.

Keeping it from wandering

A few things that actually cut down on the side quests, based on what’s worked for me and what’s floating around in these threads:

• Turn off auto-accept and review diffs before they land, at least until you trust it on a given codebase
• State the boundary explicitly in the prompt: which files it can touch, which it can’t
• Drop the effort dial for small, well-scoped tasks so it has less room to wander
• Per Anthropic’s own guidance, strip out the extra verification instructions you were adding for older models. Adding them back tends to make the over-checking worse
• Ask for a plan first on anything nontrivial, and approve the plan before it starts editing

So is it actually bad?

Depends who you ask, and what you’re asking it to do. Game-adjacent generation and Three.js environments get genuine praise. MindStudio put Opus 5 head to head with GPT-5.6 on the same prompt and found Opus 5 producing landscapes, lighting, and textures close to AAA quality, while the game underneath had backwards controls and unclear hit detection. GPT-5.6’s looked worse and played correctly. That split, gorgeous output paired with shaky fundamentals, might be the most honest summary of this whole launch. Opus 5 is genuinely strong in some places and frustrating in others, and “unusable” keeps showing up in thread titles.

If you’re evaluating whether to switch, read the threads above alongside the benchmark chart Anthropic put out on release day. Then run your own worst-case task through it before you trust it with anything that matters.