Claude Sonnet 4.5: agents that keep going
Four months after Claude 4, the time AI can stay productive on a single complex task has jumped again. That changes what a small, well-run team can build.
By the Xuru Technologies team · 30 September 2025
Key takeaways
- On 29 September 2025 Anthropic released Claude Sonnet 4.5, describing it as the best coding model in the world.
- Anthropic said it observed the model maintaining focus for more than 30 hours on complex multi-step tasks.
- It also released the Claude Agent SDK and updates to Claude Code.
- Clear specifications, tests and review remain essential as agents take on longer work.
The trend line is clear: each release lets AI handle bigger chunks of work. The bottleneck is shifting to how well people define and check that work.
What happened
TechCrunch and Decrypt covered the launch, including improvements in computer use and agentic tasks and pricing unchanged from the previous Sonnet model.
What it means for businesses
- Bigger projects, smaller teams. Migrations, refactors and feature builds move faster.
- Quality systems matter. Automated tests and code review catch what agents miss.
- Specs are the new code. Clear requirements produce better AI output.
- Buyers benefit from faster delivery when partners use these tools with discipline.
How to run an agent-assisted project
| Phase | Human role |
|---|---|
| Specification | Define goals, constraints, acceptance tests |
| Planning | Review and approve the agent's plan |
| Build | Checkpoints; review diffs |
| Release | Test, accessibility and security checks; sign-off |
Frequently asked questions
Does this mean software will be built without developers?
No. Developers increasingly direct, review and integrate AI work, focusing on architecture, quality and business logic.
Is AI-written code secure?
Only if reviewed and tested. Treat it like code from a new team member.
Will projects get cheaper?
Routine development gets faster. Savings depend on how well the project is specified and managed.
Faster delivery, human sign-off.
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