feat: Add reasoning budget support to Bedrock models for extended thinking (#4201)

[hannesrudolph]

Description

Fixes #4201

Adds comprehensive Extended Thinking (reasoning budget) support for AWS Bedrock Claude models (Sonnet 4, Opus 4, and 3.7 Sonnet). This implementation provides the equivalent functionality to the "Enable Reasoning Mode" available in the direct Anthropic provider, but integrated with AWS Bedrock's API structure.

Changes Made

🎯 Core Implementation

• Added supportsReasoningBudget: true to Claude models in packages/types/src/providers/bedrock.ts
• Implemented extended thinking support in src/api/providers/bedrock.ts with:
  • additionalModelRequestFields.thinking parameter support
  • Proper anthropic_version header handling
  • Dynamic budget token configuration
  • Conditional parameter exclusion (topP) when thinking is enabled

🔄 Stream Processing Enhancements

• Enhanced stream event handling to properly process reasoning content:
  • Support for reasoningContent blocks
  • Support for thinking content types
  • Proper content block indexing and formatting
  • Multiple fallback structures for AWS SDK compatibility

🧪 Comprehensive Testing

• Added extensive test suite in src/api/providers/__tests__/bedrock-reasoning.test.ts with 280 lines of tests covering:
  • Extended thinking parameter inclusion for supported models
  • Parameter exclusion for non-supported models
  • Stream processing for reasoning content
  • Multiple event structure compatibility
  • Error handling and validation

🎨 UI Improvements

• Updated ThinkingBudget component in webview-ui/src/components/settings/ThinkingBudget.tsx to:
  • Properly calculate max token limits for Bedrock models
  • Show reasoning budget controls when supportsReasoningBudget is true
  • Integrate with existing reasoning effort settings
• Fixed ApiOptions component to conditionally render ThinkingBudget only when models are available
• Improved Bedrock provider settings layout and conditional rendering

🛠️ Error Handling

• Added VALIDATION_ERROR handling for parameter validation issues
• Enhanced error messaging with specific guidance for extended thinking problems
• Improved logging for debugging extended thinking requests

Technical Implementation Details

API Integration

The implementation follows AWS Bedrock's official extended thinking specification:

additionalModelRequestFields: {
  thinking: {
    type: "enabled",
    budget_tokens: metadata?.thinking?.maxThinkingTokens || modelConfig.reasoningBudget || 4096
  }
}

Stream Processing

Handles multiple AWS SDK event structures:

• contentBlock.reasoningContent.text (official AWS docs structure)
• contentBlock.type === "thinking" (alternative structure)
• delta.reasoningContent.text and delta.thinking (delta events)

Model Support

Enabled for:

• anthropic.claude-sonnet-4-20250514-v1:0
• anthropic.claude-opus-4-20250514-v1:0
• anthropic.claude-3-7-sonnet-20250219-v1:0

Testing Performed

• ✅ All existing tests pass - verified backward compatibility
• ✅ New test suite passes - 280 lines of reasoning-specific tests
• ✅ Manual testing completed:
  • Extended thinking activates correctly for supported models
  • Reasoning content renders properly in the UI
  • Settings UI shows/hides controls appropriately
  • Parameter validation works correctly
  • Error handling provides helpful messages

Verification of Acceptance Criteria

From issue #4201:

• ✅ Models show reasoning support: Instead of :thinking variants, models now support reasoning budget configuration
• ✅ Enable Reasoning Mode equivalent: ThinkingBudget component provides the same functionality as Anthropic provider
• ✅ Max Thinking Tokens configuration: Fully configurable budget with appropriate limits
• ✅ Extended thinking triggers: Reasoning now activates correctly when enabled and supported
• ✅ UI consistency: Matches the pattern established by other providers

Checklist

• ✅ Code follows project style guidelines
• ✅ Self-review completed
• ✅ Comments added for complex logic (stream processing, reasoning detection)
• ✅ No breaking changes to existing Bedrock functionality
• ✅ Comprehensive test coverage for new functionality
• ✅ Error handling covers edge cases and provides helpful messages
• ✅ UI changes are consistent with existing design patterns
• ✅ Performance impact minimal (only adds parameters when needed)

Related Issues

• Fixes AWS Bedrock does not show or support Sonnet and Opus 4 Extended Thinking #4201: AWS Bedrock does not show or support Sonnet and Opus 4 Extended Thinking
• Related to Support extended thinking for Claude 3.7/4 models in Bedrock #4279: Support extended thinking for Claude 3.7/4 models in Bedrock (closed as duplicate)

Screenshots/Demo

Before: No reasoning budget controls visible for Bedrock models
After: ThinkingBudget component appears for supported Bedrock models, matching Anthropic provider functionality

Users can now:

1. Select a supported Claude model in Bedrock
2. See the "Enable Reasoning Mode" toggle and token budget slider
3. Configure reasoning parameters just like with the direct Anthropic provider
4. Experience extended thinking in their conversations with proper reasoning content rendering

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Important

Adds reasoning budget support to AWS Bedrock models, enabling extended thinking capabilities with updated configurations, stream processing, UI, and error handling.

• Behavior:
  • Adds supportsReasoningBudget: true to Claude models in bedrock.ts.
  • Implements extended thinking in bedrock.ts with additionalModelRequestFields.thinking and dynamic budget token configuration.
  • Excludes topP parameter when thinking is enabled.
• Stream Processing:
  • Enhances stream event handling in bedrock.ts to process reasoningContent and thinking content types.
• Testing:
  • Adds tests in bedrock-reasoning.test.ts for reasoning parameter inclusion, stream processing, and error handling.
• UI:
  • Updates ThinkingBudget.tsx to calculate max token limits and show reasoning budget controls.
  • Updates ApiOptions.tsx to conditionally render ThinkingBudget.
• Error Handling:
  • Adds VALIDATION_ERROR handling for parameter validation issues in bedrock.ts.

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[daniel-lxs]

LGTM with emphasis on "looks" cause I don't have a way to test this.

[hannesrudolph]

I tested it