Claude Opus 4.5 is Anthropic's frontier reasoning model released in November 2025, optimized for complex software engineering, agentic workflows, and long-horizon computer use. It offers strong multimodal capabilities, improved robustness to prompt injection, and a new effort parameter that lets developers trade off speed, depth, and token usage depending on task requirements. The model excels at autonomous research, multi-step debugging, spreadsheet and browser manipulation, and coordinated multi-agent setups, delivering substantial gains in structured reasoning and execution reliability.