Anthropic's Claude Sonnet 4.5 is Live in Cline

Claude Sonnet 4.5 by Anthropic is now available in Cline. After testing early with Anthropic, we're seeing a model built for sustained autonomous work that delivers on what developers actually need: less talk, more code. With a 200k context window at the same $3/$15 pricing as Sonnet 4, this update represents a refinement in how AI models approach real software development.

A Model That Just Ships

Claude Sonnet 4.5 operates differently than prior iterations. Where previous models might narrate every step, explain their thinking, and celebrate small victories, Sonnet 4.5 gets to work. It's noticeably more terse, jumping straight to implementation without the play-by-play commentary.

The model delivers fact-based progress reports when needed, stays quiet when executing, and only speaks up when it genuinely needs clarification.

The model still communicates, but purposefully. When it encounters ambiguity, it asks specific questions with options. When it's implementing, it chains file reads and modifications without interruption. The result is a workflow that feels more like pair programming with an experienced colleague than managing an eager intern.

Built for the Long Haul

The real breakthrough with Sonnet 4.5 is its ability to maintain coherence across extended work sessions. The model demonstrates exceptional state tracking, naturally saving progress in external files like progress.txt or implementation_notes.md, leaving notes for future sessions, and using git to maintain continuity.

This isn't just about having a good memory; it's about working like a professional developer. Sonnet 4.5 can work on a complex feature for an entire context window, properly save its state, then pick up in a fresh session exactly where it left off. It reads its own progress notes, checks git logs, runs through test suites, and continues implementation without missing a beat.

The model also sets up its own quality-of-life tooling. It creates init scripts to gracefully start servers, maintains test suites in structured formats, and builds the scaffolding it needs to work efficiently across sessions.

Getting the Most from Sonnet 4.5

A few tips from our testing:

Be explicit about intent. If you want implementation, say "implement these changes" rather than "can you suggest changes." The model precisely follows instructions, so clarity yields better results.

For complex tasks, let the model set up comprehensive tests. It excels at creating test harnesses that guide implementation and ensure correctness throughout the work.

Trust its ability to maintain state. You don't need to remind it of context or re-explain requirements when continuing work across sessions. The model's state tracking is remarkably robust.

When you want more visibility into its thinking, just ask. The model can adjust its verbosity based on your preferences, from completely silent execution to detailed explanations of its approach.

A Natural Fit for Cline

Sonnet 4.5's improvements align naturally with how developers use Cline for complex work. The model's terseness means less context pollution as tasks progress. Its state management capabilities - writing progress files, maintaining test suites, using git effectively - work seamlessly within Cline's environment.

When Cline's Auto Compact compresses conversation history, Sonnet 4.5's habit of maintaining external state files provides an additional continuity layer. Focus Chain keeps the task on track while the model handles its own memory. It's not that we designed these features for each other; they just work well together.

The model is available now in Cline as claude-sonnet-4-5-20250929. Same pricing as Sonnet 4 at $3 per million input tokens and $15 per million output tokens.

Ready to experience a model that focuses on shipping code? Update Cline and select Sonnet 4.5 today. Share your experiences with complex, multi-session projects on Reddit or Discord.