Claude Sonnet 4.5: What It Does and Why It Matters

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Here’s what it actually offers, what it’s good at, and where it fits into the current landscape of AI tools.

First, what is Claude Sonnet 4.5?

Claude Sonnet 4.5 is a mid-tier model in Anthropic’s Claude family. It’s meant to replace the previous Sonnet 4, and in many ways, it performs better than even their higher-end Opus 4.1 model. Despite that, it keeps the same price as Sonnet 4:

• $3 per million input tokens

• $15 per million output tokens

Anthropic says it’s the best option for almost all use cases, and based on early results, that claim seems reasonable.

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The coding side is where it really stands out

Sonnet 4.5 is built with coding in mind. And it’s very good at it.

• It scored 77.2% on SWE-bench Verified, which is a benchmark for real-world software engineering problems. That’s the best score of any model so far.

• It can work on coding tasks for more than 30 hours straight without losing track of what it’s doing. That’s a big deal for long-running workflows or autonomous agents.

• In practice, it seems to reduce coding error rates significantly. One report showed errors dropping from 9% (with Sonnet 4) to nearly zero with Sonnet 4.5.

In one example, it built a working Stripe integration in 15 minutes. GPT-5 Codex took over an hour for the same task. And the code Sonnet wrote wasn’t just fast—it was clean and easier to build on.

That kind of reliability and speed means less cleanup later and a smoother development process overall.

It's not just for code

Yes, Sonnet 4.5 is great for developers, but it’s also solid across a wide range of tasks.

For writing and editing

Writers will find it more useful than previous models. It’s better at suggesting outlines, improving drafts, and editing messy text into something usable. One person said it was the first model to rewrite a bad scene into something they actually liked.

Is it as strong as Opus 4.1 when it comes to creative writing? Not quite. But it’s close—and much cheaper to run.

For business work

It handles everyday business tasks well: spreadsheets, presentations, and reports. But it also has range. Financial analysts have used it to track regulations, update compliance rules, and handle risk assessments.

For long-form content

If you need long, structured output—like blog posts, reports, or technical documentation—Sonnet 4.5 does a better job than most. In one test, it wrote a 4,000-word article that was clean, clear, and well-organized.

The tools that come with it are worth a look

Anthropic didn’t just drop a new model. They added some helpful tools alongside it.

1. Claude Agent SDK

This lets developers build advanced AI agents that can manage tasks, store memory, and work across systems. It’s the same toolkit Anthropic uses internally.

You can set up permissions, coordinate sub-agents, and keep things running without rewriting everything from scratch.

2. VS Code extension + Claude Code

Sonnet 4.5 is now available inside Visual Studio Code. That means it’s easier for developers to use it without switching tools.

Claude Code also got some updates, including a checkpoint system. You can now save your progress and roll back if something goes wrong. It also has a better terminal interface.

3. Memory Tool + Context Awareness

One of the most useful additions is memory. The model can now create and manage files as if they were notes it keeps on the side. This helps it stay on track during longer projects.

It also understands how much of its context window it’s using, which helps it manage big conversations or long-running workflows more effectively.

4. Imagine with Claude (research preview)

This is still early, but promising. It lets Claude generate and modify software in real-time. You interact with the app, and Claude updates the code instantly.

It’s not polished yet, but if you’re prototyping or brainstorming an idea, it’s a fun way to explore new directions quickly.

5. How to access it

Sonnet 4.5 is available across platforms:

• Claude.ai (web and mobile)

• Claude API for developers

• Amazon Bedrock

• Google Cloud Vertex AI

• GitHub Copilot (preview access in some plans)

So, is it worth using?

If you work with code, the answer is yes. Sonnet 4.5 is fast, consistent, and noticeably better than what came before. It handles long tasks, avoids common bugs, and writes code that people actually want to use.

If you’re a writer, researcher, or someone who depends on structured, thoughtful output, it’s also a strong choice—especially for the price.

It may not be the absolute best at everything. For high-end creative work, Opus or GPT-5 might still edge it out. But for most day-to-day tasks, Sonnet 4.5 is a reliable, efficient model that gets the job done.

And the fact that it can run for 30+ hours without dropping the ball? That opens up new possibilities for agents and tools that need to stay sharp across long projects.

Final thoughts

Claude Sonnet 4.5 isn’t flashy. It doesn’t try to sell you magic. But it works well, stays focused, and handles real tasksbetter than most models out there. That’s what makes it stand out.

For developers, businesses, and anyone who wants an AI assistant that can keep up without falling apart halfway through the job, this release is worth a serious look.

No hype. Just solid progress.