Claude 4.5 Sonnet : Bye bye Software Devs
Claude 4.5 Sonnet is the best coding LLM now
Claude Sonnet 4.5 isn’t just another LLM release, it’s now the best coding model available.
Stronger at software development, sharper at reasoning, and surprisingly good at handling math-heavy work. Where most models still stumble after a few steps,
https://medium.com/media/898ee171cb74e9a9b68f690f2af30af4/href
Sonnet 4.5 sustains focus across 30+ hour multi-step tasks. That’s unheard of.
Code isn’t just about writing functions anymore. It’s about using the computer like a real collaborator: executing commands, editing files, filling spreadsheets, generating slides. Sonnet 4.5 nails this. On OSWorld, the benchmark that tests computer-use, it now leads at 61.4%, compared to Sonnet 4’s 42.2% just four months ago. On SWE-bench Verified, which measures real-world software engineering tasks, it sits firmly at the top. This is where it earns the title of best coding model.
Product Upgrades Around It
Anthropic didn’t just ship the model, they overhauled the ecosystem.
- Claude Code: checkpoints (finally), a better terminal, and a native VS Code extension.
- Claude API: context editing plus a memory tool so agents can run longer and juggle more complexity.
- Claude Apps: code execution and file creation (docs, spreadsheets, slides) baked right into the conversation.
- Claude for Chrome: live for Max users, showing Sonnet working directly in the browser.
These aren’t just shiny add-ons, they’re the plumbing you need if you want to build serious agents.
The Claude Agent SDK
This is probably the most important release outside the model itself. Anthropic is giving away the same infrastructure they use internally to run Claude Code. The SDK handles the messy but essential parts of agent design:
- memory management for long sessions,
- permissioning that balances autonomy with control,
- subagent coordination across complex tasks.
Anyone building their own agents now has access to the same backbone. That’s a big shift from “we build tools” to “you build with our tools.”
Alignment and Safety
Claude Sonnet 4.5 isn’t just stronger, it’s also more aligned. Compared to previous Claude models, it shows fewer cases of sycophancy, deception, power-seeking, and delusion-support.
They’ve added AI Safety Level 3 (ASL-3) protections, with classifiers filtering out high-risk requests like CBRN-related queries (chemical, biological, radiological, nuclear). False positives are still an issue, but they’ve cut them down by a factor of 10 compared to earlier releases.
They’ve also done something new: integrating mechanistic interpretability techniques into safety evaluations. This is a more transparent way of stress-testing the model’s internals, not just its surface outputs.
Research Preview: Imagine with Claude
Alongside Sonnet 4.5, Anthropic released a short-lived preview called Imagine with Claude. It generates software live, no pre-baked functions, adapting in real time as you interact. It’s more a proof-of-concept than a product, but it shows where agentic coding could head.
Pricing and Availability
Claude Sonnet 4.5 is available everywhere now. Pricing stays the same as Sonnet 4, $3/$15 per million tokens through the Claude API. For most developers, it’s a straight swap: you can call claude-sonnet-4-5 today and get stronger coding, longer focus, and better reasoning for the same cost.
Final Take
Claude Sonnet 4.5 isn’t just a model upgrade, it’s a full-stack release: the model, the SDK, the safety scaffolding, and the product integrations. If you’re building agents, this is the best foundation you can pick right now.
Model Context Protocol: Advanced AI Agents for Beginners (Generative AI books)
Claude 4.5 Sonnet : Bye bye Software Devs was originally published in Data Science in Your Pocket on Medium, where people are continuing the conversation by highlighting and responding to this story.
