Extended Thinking Support for Sonnet 4.5

What: Claude Code now supports extended thinking mode when using Claude Sonnet 4.5, enabling more transparent reasoning for complex tasks.

How to use:

# Enable thinking via environment variable
MAX_THINKING_TOKENS=10000 claude

# Or configure in your settings file
# Set alwaysThinkingEnabled: true in your Claude Code settings

Details:

• Only available when using Claude Sonnet 4.5 model
• Can be controlled via MAX_THINKING_TOKENS environment variable (set to any positive integer to enable)
• Can be configured permanently via alwaysThinkingEnabled in settings
• Subject to Statsig feature gate thinking_on_default for gradual rollout
• Provides visible reasoning steps during Claude's problem-solving process
• Evidence: hL1() at line 364041 in v2.0.5