Opus 5 Defaults to High Effort in Claude Code with New Fast Mode
Anthropic has announced that its Opus 5 model now defaults to "high effort" reasoning within Claude Code and the Claude Platform. Additionally, a new "Fast mode" has been introduced, offering 2.5x faster speeds at double the base price. This update allows developers to leverage deeper reasoning capabilities by default for complex coding tasks, while providing flexibility to scale down compute for faster, cheaper iterations. It highlights the industry trend of giving users control over test-time compute and reasoning effort. The new Fast mode operates at approximately 2.5 times the speed of the default mode but incurs a cost of 2 times the base price on the Claude Platform and via extra usage in Claude Code. Users can adjust the effort level up for difficult problems or down to save time and API costs.
## BACKGROUND
Claude Code is Anthropic's agentic command-line tool designed to help developers write, edit, and test code directly within their terminal and codebase. Reasoning models utilize test-time compute, allowing them to "think" before responding, and controlling "reasoning effort" lets developers balance output quality against latency and API costs.