Anthropic recently unveiled Claude 4 (Opus and Sonnet), achieving record-breaking 72.7% performance on SWE-bench Verified and surpassing OpenAI’s latest models. Benchmarks aside, I wanted to see how Claude 4 holds up under real-world software engineering tasks. I spent the last 24 hours putting it through intensive testing with challenging refactoring scenarios.

I tested Claude 4 using a Rust codebase featuring complex, interconnected issues following a significant architectural refactor. These problems included asynchronous workflows, edge-case handling in parsers, and multi-module dependencies. Previous versions, such as Claude Sonnet 3.7, struggled here—often resorting to modifying test code rather than addressing the root architectural issues.

Claude 4 impressed me by resolving these problems correctly in just one attempt, never modifying tests or taking shortcuts. Both Opus and Sonnet variants demonstrated genuine comprehension of architectural logic, providing solutions that improved long-term code maintainability.

Key observations from practical testing:

• Claude 4 consistently focused on the deeper architectural causes, not superficial fixes.

• Both variants successfully fixed the problems on their first attempt, editing around 15 lines across multiple files, all relevant and correct.

• Solutions were clear, maintainable, and reflected real software engineering discipline.

I was initially skeptical about Anthropic’s claims regarding their models' improved discipline and reduced tendency toward superficial fixes. However, based on this hands-on experience, Claude 4 genuinely delivers noticeable improvement over earlier models.

For developers seriously evaluating AI coding assistants—particularly for integration in more sophisticated workflows—Claude 4 seems to genuinely warrant attention.

A detailed write-up and deeper analysis are available here: Claude 4 First Impressions: Anthropic’s AI Coding Breakthrough

Interested to hear others' experiences with Claude 4, especially in similarly challenging development scenarios.

Been using ChatGPT Plus with o3 and Gemini 2.5 Pro for coding the past months. Both are decent but always felt like something was missing, you know? Like they'd get me 80% there but then I'd waste time fixing their weird quirks or explaining context over and over or running in a endless error loop.

Just tried Claude 4 Opus and... damn. This is what I expected AI coding to be like.

The difference is night and day:

• Actually understands my existing codebase instead of giving generic solutions that don't fit

• Debugging is scary good - it literally found a memory leak in my React app that I'd been hunting for days

• Code quality is just... clean. Like actually readable, properly structured code

• Explains trade-offs instead of just spitting out the first solution

Real example: Had this mess of nested async calls in my Express API. ChatGPT kept suggesting Promise.all which wasn't what I needed. Gemini gave me some overcomplicated rxjs nonsense. Claude 4 looked at it for 2 seconds and suggested a clean async/await pattern with proper error boundaries. Worked perfectly.

The context window is massive too - I can literally paste my entire project and it gets it. No more "remember we discussed X in our previous conversation" BS.

I'm not trying to shill here but if you're doing serious development work, this thing is worth every penny. Been more productive this week than the entire last month.

Got an invite link if anyone wants to try it: https://claude.ai/referral/6UGWfPA1pQ

Anyone else tried it yet? Curious how it compares for different languages/frameworks.

EDIT: Just to be clear - I've tested basically every major AI coding tool out there. This is the first one that actually feels like it gets programming, not just text completion that happens to be code. This also takes Cursor to a whole new level!