Claude Sonnet 4.5
Anthropic's Claude Sonnet 4.5 delivers world-leading coding (77.2% SWE-bench) and a 200K context window, optimized for the next generation of autonomous agents.
anthropicClaude 4September 29, 2025Your AI response will appear here
About Claude Sonnet 4.5
Learn about Claude Sonnet 4.5's capabilities, features, and how it can help you achieve better results.
**The Frontier of Agentic Intelligence**
Claude Sonnet 4.5 represents Anthropic’s most significant leap in "frontier intelligence," specifically optimized for the era of autonomous AI agents. Released in late 2025, it is the industry's first true "hybrid reasoning" model, allowing developers to toggle between high-speed execution for routine tasks and extended thinking for complex logical challenges. It notably eclipsed previous benchmarks in computer use and tool orchestration, making it the preferred engine for terminal-based agents and multi-file software engineering.
**Precision and Reduced Hallucinations**
The model is built on an architecture that prioritizes "measure twice, cut once" logic, significantly reducing the sycophancy and hallucinations seen in the 3.5 series. With a massive 64,000-token output limit and a 200,000-token input window, it can ingest entire repositories while generating full-length application files in a single pass. It also introduces native "checkpoints" for agentic workflows, allowing agents to roll back and correct their own mistakes autonomously.
**Multimodal and Reasoning Prowess**
Beyond coding, Sonnet 4.5 dominates in multimodal document analysis and complex financial modeling. Its internal logic is trained to prioritize architectural context, enabling it to map out large-scale codebases better than any predecessor. Whether processing handwritten notes or implementing a full Stripe integration, Sonnet 4.5 maintains a high level of factual accuracy and instruction following.
Use Cases for Claude Sonnet 4.5
Discover the different ways you can use Claude Sonnet 4.5 to achieve great results.
Autonomous Software Engineering
Use Claude Sonnet 4.5 to navigate complex codebases, implement features across multiple files, and run tests independently.
Computer-Use Agents
Deploy the model to control desktops and web browsers for data extraction, legacy system navigation, or repetitive administrative tasks.
Enterprise Agentic Search
Orchestrate multi-step search queries and synthesize disparate information from internal documentation and the live web.
Complex Financial Modeling
Leverage its 87% AIME score to perform deep logical deductions on financial reports and market data.
Technical Content Refinement
Convert high-level requirements into professional PRDs, technical specifications, and copy-paste-ready codebases.
Multimodal Document Analysis
Process thousands of pages of charts, handwritten notes, and technical diagrams with state-of-the-art vision capabilities.
Strengths
Limitations
API Quick Start
anthropic/claude-sonnet-4.5
import Anthropic from '@anthropic-ai/sdk';
const anthropic = new Anthropic({
apiKey: process.env.ANTHROPIC_API_KEY,
});
const msg = await anthropic.messages.create({
model: "claude-sonnet-4.5-20250929",
max_tokens: 1024,
messages: [{ role: "user", content: "Implement a rate limiter in Node.js" }],
});
console.log(msg.content[0].text);Install the SDK and start making API calls in minutes.
What People Are Saying About Claude Sonnet 4.5
See what the community thinks about Claude Sonnet 4.5
"Claude Sonnet 4.5 is the new king of AI coding... it is looking really, really good"
"Sonnet 4.5 is doing a really good job... it was faster by a lot and better by a decent amount"
"I'm blown away by Sonnet 4.5... this one is designing some absolutely stunning pages"
"The terminal-based agent is a 'developer living in your terminal'... it can read codebases and run tests autonomously"
"Pricing remains the same as 3.5, but the 'Checkpoints' feature makes it worth 10x more for professional workflows"
"At 77.2% on SWE-bench, this is the first model that actually feels like a Senior Engineer"
Videos About Claude Sonnet 4.5
Watch tutorials, reviews, and discussions about Claude Sonnet 4.5
“Anthropic claims this is the 'best code model in the world' with substantial gains in reasoning, math, and computer use.”
“While GPT-5 might be better for high-level planning, Claude 4.5 Sonnet is currently the 'nicest' model to use for implementation.”
“The speed is just incredible, making interactive coding feel much more fluid.”
“It handles multi-file edits with a level of precision we haven't seen before.”
“The reduction in hallucinations makes it a reliable partner for production code.”
“Claude Sonnet 4.5 was faster by a lot and better by a decent amount than GPT-5 Codex.”
“It did the entire Stripe implementation in 15 minutes... more than two times faster than Opus 4.1.”
“The ability to follow complex tool-calling instructions is its secret sauce.”
“I'm seeing fewer 'sycophancy' issues where the model just agrees with my bad ideas.”
“This is the first model I'd actually trust to run a terminal-based agent unsupervised.”
“This is one of the best landing pages, if not THE best landing page, I've ever seen created from a prompt.”
“It's an absolute beast... it is designing some absolutely stunning pages with really, really nice code.”
“The vision capabilities for interpreting UI design are significantly upgraded.”
“It feels like it understands the aesthetic requirements, not just the technical ones.”
“Sonnet 4.5 is officially the new benchmark for creative front-end engineering.”
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Pro Tips
Expert tips to help you get the most out of this model and achieve better results.
Leverage CLAUDE.md
Use a CLAUDE.md file in your repository root to give the model short summaries and pointers; this reduces token waste by 30%.
Hybrid Reasoning Toggle
Use the 'thinking' parameter in your API calls only for logic-heavy tasks to save on latency and costs during routine operations.
The .claude/context Folder
Create a .claude/context.md file to store architectural decisions; the model is specifically trained to prioritize this path for codebase mapping.
Prompt Caching
Enable prompt caching for static documentation or large codebases to save up to 90% on input costs for repeated queries.
Testimonials
What Our Users Say
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Frequently Asked Questions
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