ADR-047: Fast Mode Integration for Claude Code

Status: Proposed Date: 2026-02-08 Authors: RuvNet, Claude Flow Team

Context

Claude Code has introduced Fast Mode as a research preview feature that provides faster Opus 4.6 responses at higher cost. This feature is valuable for interactive work where latency matters more than cost, such as rapid iteration and live debugging.

What is Fast Mode?

Fast Mode is not a different model - it uses the same Opus 4.6 with a different API configuration that prioritizes speed over cost efficiency. Users get identical quality and capabilities, just faster responses.

Key Characteristics

Pricing (Research Preview)

Note: 50% discount available until Feb 16, 2026 11:59pm PT.

Decision

Integrate Fast Mode awareness into RuvFlow/Claude-Flow to enable:

1. Automatic Fast Mode for time-critical swarm tasks
2. Settings integration for user preference management
3. Cost-aware routing that considers fast mode pricing
4. Statusline indicator showing fast mode state

Integration Points

1. Settings Generator Update

Add fast mode configuration to .claude/settings.json:

{
  "fastMode": false,
  "claudeFlow": {
    "fastMode": {
      "enabled": false,
      "autoEnable": {
        "forDebugTasks": true,
        "forInteractiveSessions": true,
        "forTimeCriticalTasks": true
      },
      "costWarning": true,
      "fallbackBehavior": "continue"
    }
  }
}

2. Routing Intelligence

Update the 3-tier routing model (ADR-026) to include fast mode consideration:

3. CLI Hooks

Add fast mode hooks for swarm coordination:

# Pre-task hook checks if fast mode should be enabled
npx ruvflow hooks pre-task --enable-fast-mode-if-critical

# Post-task hook can disable fast mode to save costs
npx ruvflow hooks post-task --restore-standard-mode

4. Swarm Coordination

For swarm tasks, fast mode decisions should consider:

• Task urgency: Enable for live debugging, disable for batch processing
• Budget constraints: Check remaining extra usage credits
• Rate limits: Handle automatic fallback gracefully

Fast Mode vs Effort Level

These are complementary settings:

Rate Limit Handling

When fast mode rate limits are hit:

1. Fast mode automatically falls back to standard Opus 4.6
2. The ↯ icon turns gray (cooldown indicator)
3. Work continues at standard speed/pricing
4. Fast mode auto-re-enables when cooldown expires

RuvFlow should detect this and:

• Log the fallback event
• Adjust cost tracking accordingly
• Notify swarm coordinator of reduced speed

Consequences

Positive

1. Faster interactive sessions: 2-5x faster responses for debugging
2. Flexible cost/speed tradeoff: Users control when to prioritize speed
3. Better UX: Reduced waiting during rapid iteration
4. Swarm optimization: Time-critical tasks complete faster

Negative

1. Higher costs: 2x token pricing in fast mode
2. Extra usage required: Not included in subscription limits
3. Team/Enterprise friction: Requires admin enablement
4. Complexity: Another dimension in routing decisions

Neutral

1. Same model quality: No accuracy tradeoff
2. Research preview: Feature may change

Implementation

Phase 1: Awareness (Settings)

// types.ts - Add fast mode types
interface FastModeConfig {
  enabled: boolean;
  autoEnable: {
    forDebugTasks: boolean;
    forInteractiveSessions: boolean;
    forTimeCriticalTasks: boolean;
  };
  costWarning: boolean;
  fallbackBehavior: 'continue' | 'pause' | 'notify';
}

Phase 2: Settings Generator

Update settings-generator.ts:

// Add to generateSettings()
settings.fastMode = options.fastMode?.enabled || false;

settings.claudeFlow.fastMode = {
  enabled: options.fastMode?.enabled || false,
  autoEnable: {
    forDebugTasks: true,
    forInteractiveSessions: true,
    forTimeCriticalTasks: true,
  },
  costWarning: true,
  fallbackBehavior: 'continue',
};

Phase 3: Routing Integration

Update pre-task hook to consider fast mode:

// In hooks/pre-task.ts
async function shouldEnableFastMode(task: TaskDescription): Promise<boolean> {
  const config = await loadFastModeConfig();

  if (!config.enabled) return false;

  // Check task characteristics
  if (config.autoEnable.forDebugTasks && task.isDebugTask) return true;
  if (config.autoEnable.forTimeCriticalTasks && task.priority === 'critical') return true;
  if (config.autoEnable.forInteractiveSessions && isInteractiveSession()) return true;

  return false;
}

Phase 4: Statusline Integration

Update statusline to show fast mode state:

// In statusline.cjs
const fastModeIndicator = fastModeEnabled ? '↯' : '';
const modelDisplay = `${modelName}${fastModeIndicator}`;

Phase 5: Documentation

Update CLAUDE.md with fast mode guidance:

## Fast Mode

Enable fast mode for time-critical tasks:

\`\`\`bash
# Toggle in Claude Code
/fast

# Or in settings
"fastMode": true
\`\`\`

**Cost:** 2x standard Opus 4.6 pricing
**Best for:** Live debugging, rapid iteration, tight deadlines
**Avoid for:** Batch processing, CI/CD, cost-sensitive workloads

Alternatives Considered

1. Always Use Fast Mode

Pros: Maximum speed Cons: 2x costs, not always needed Decision: Rejected - costs would be prohibitive for long tasks

2. Ignore Fast Mode

Pros: Simpler implementation Cons: Miss performance optimization opportunity Decision: Rejected - users expect modern feature support

3. Auto-Detect and Enable

Pros: Zero user configuration Cons: Unpredictable costs, user may not want it Decision: Rejected - cost control requires explicit opt-in

Migration

No migration needed - this is an additive feature. Existing users:

• Default: fast mode disabled
• Opt-in: Enable via settings or /fast command

Metrics for Success

References

• Source: https://code.claude.com/docs/en/fast-mode
• Related: ADR-026 (3-Tier Model Routing)
• Related: ADR-018 (Claude Code Integration)

Appendix: CLI Reference

Commands

Settings

{
  "fastMode": true,
  "claudeFlow": {
    "fastMode": {
      "enabled": true,
      "autoEnable": {
        "forDebugTasks": true,
        "forInteractiveSessions": true,
        "forTimeCriticalTasks": true
      },
      "costWarning": true,
      "fallbackBehavior": "continue"
    }
  }
}

Rate Limit Behavior

1. Fast mode has separate rate limits from standard Opus
2. On rate limit: automatic fallback to standard Opus
3. Visual indicator: ↯ icon turns gray during cooldown
4. Auto-recovery: fast mode re-enables when cooldown expires

Decision Date: 2026-02-08 Review Date: 2026-03-08 (30 days post-implementation)