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If you're wondering whether Claude Sonnet 4.5 is actually better than version 4, or if it's just marketing hype, I've got answers.
GitHub Repo: https://github.com/Cubent-Dev/Claude-Sonnet-4-vs-4.5-Research
If you're wondering whether Claude Sonnet 4.5 is actually better than version 4, or if it's just marketing hype, I've got answers.
I threw 100 questions at both models, math problems, coding challenges, logic puzzles, and general knowledge stuff. Here's what I found.
Claude Sonnet 4.5 is legitimately better. Not by a little bit, either. We're talking 11.3% more accurate across the board, and it's faster too. Yeah, I was surprised.
Got things right about 76% of the time
Average response time: 2.92 seconds
Got things right about 87% of the time
Average response time: 2.52 seconds
So 4.5 is roughly 11% more accurate and about half a second faster. That might not sound huge, but when you're working with these models all day, it adds up fast.
I tested four different areas to see where the improvements actually matter:
Mathematics (25 questions)
Sonnet 4: 74.1%
Sonnet 4.5: 87.1%
Improvement: 13%
This was probably the biggest surprise. The newer model just handles complex math way better. Multi-step problems that would trip up version 4 are no problem for 4.5.
Programming (25 questions)
Sonnet 4: 76.3%
Sonnet 4.5: 86.2%
Improvement: 9.9%
Better at debugging, cleaner code, fewer stupid mistakes. If you're using Claude for coding, this upgrade matters.
Reasoning (25 questions)
Sonnet 4: 74.8%
Sonnet 4.5: 87.4%
Improvement: 12.7%
Logic puzzles, critical thinking, that kind of stuff. Version 4.5 just thinks through problems more clearly.
General Knowledge (25 questions)
Sonnet 4: 78.8%
Sonnet 4.5: 88.6%
Improvement: 9.7%
Facts, trivia, domain knowledge. Version 4 was already pretty good here, but 4.5 is better.
Here's the thing: 86 out of 100 questions showed improvement with version 4.5. That's not random chance. That's a real, consistent upgrade.
The improvements aren't just in accuracy either. The responses from 4.5 are clearer, more thoughtful, and make fewer weird mistakes. It's like the difference between someone who's pretty smart and someone who's pretty smart and pays attention to detail.
You need accurate answers (obviously)
You're working on anything technical or complex
You're building something that matters
You want faster responses without sacrificing quality
You're just messing around and testing stuff
Budget is super tight (they're priced the same though, so...)
You literally don't care about accuracy
Honestly? Just use 4.5. They cost the same, and it's objectively better in every measurable way.
Speed: I expected 4.5 to be slower because it's more capable. Nope. It's actually faster by about 0.4 seconds on average. That's wild.
Consistency: Version 4 would occasionally give really weird answers. Like, confidently wrong in bizarre ways. Version 4.5 still makes mistakes, but they're more... reasonable mistakes? Hard to explain, but you'll notice if you use both.
Math: The math improvement was huge. Like, noticeably huge. If you're doing anything with calculations or proofs, the upgrade is worth it for this alone.
Is Claude Sonnet 4.5 perfect? No. Does it still mess up sometimes? Yes. But it messes up less, thinks better, and works faster than version 4.
I ran these tests because I was genuinely curious if the new version was worth using. After 100 questions and way too many hours analyzing the results, the answer is a solid yes.
The improvement is real, it's consistent, and it's significant enough that you'll notice in actual use. Not just in benchmarks – in the stuff you're actually building.
If you're still using Claude Sonnet 4 and you have access to 4.5, switch. There's no reason not to. Better performance, same price, faster responses.
This isn't a marginal upgrade where you have to squint to see the difference. This is the kind of improvement that actually matters when you're trying to get work done.
