Claude 4.5 Opus: The 3M Context Era
April 21, 2026 • 12 Min Read
Anthropic has officially opened early access to **Claude 4.5 Opus**, setting a new benchmark for large language models with a staggering **3-million token context window**. This architectural leap allows developers to feed entire repository structures, massive legal corpora, or hours of high-definition video into a single prompt session.
Deep Reasoning Mode
The standout feature of 4.5 Opus is the new **'Deep Reasoning'** mode. Unlike standard inference, this mode utilizes an internal verification chain, where the model cross-references its own logic before generating the final token. While slower, it significantly reduces hallucinations in complex math and code generation tasks.
Benchmarks
In early testing, Claude 4.5 Opus achieved a **91.2% score on the SWE-Bench Verified**, outperforming its predecessor by nearly 15%. Its ability to handle long-range dependencies makes it the ideal engine for **Autonomous Coding Agents** that need to understand global state across thousands of files.
Key Technical Specs
- Context Window: 3,000,000 Tokens
- Max Output: 16,384 Tokens
- Architecture: Sparse Mixture-of-Experts (MoE)
- Optimization: Deep Reasoning Verification
Access is currently being rolled out to **Claude Pro** and **Team** users, with API availability via the **Anthropic Console** and **Amazon Bedrock** following in early May.