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.