Claude Code Complete Source Code Leaked: What I Found After Reading All 510,000 Lines

Today's Big News (March 31, 2026): Anthropic's Claude Code Complete Source Code Leaked

Tech Stack First

Agentic Loop: A Single while(true) Powers the Entire Agent

async function* queryLoop(params) {
  let state = { messages, toolUseContext, turnCount: 1, ... }
  while (true) {
    // 1) Preprocessing: trim history, compress context, prefetch memory and skills
    // 2) Call Claude API (streaming)
    // 3) Stream output while watching for tool_use blocks
    // 4) If tool_use found → check permissions → execute → push result to messages → back to while
    // 5) No tool calls → exit
  }
}

Context Management: Not One-Size-Fits-All, But Four Surgical Knives

1. HISTORY_SNIP: The finest granularity—directly deletes certain messages without summarization. For example, if a tool returns 500 lines of search results but the model only uses 3 lines, the remaining 497 lines are pure noise. Keeping them wastes tokens; summarizing them also wastes tokens. Deletion is the most economical choice.
2. Microcompact: Leverages API-layer capabilities to edit at the cache level. It doesn't modify message content but tells the API "these tokens are in your cache but don't use them." This reduces token count without touching the messages.
3. CONTEXT_COLLAPSE: "Archives" old conversation turns into summaries, maintaining a git log-like structure. Each new query replays this structure. Unlike autocompact, it preserves structure—what happened in which turn and what conclusions were reached remain clear, not mashed into a single summary blob.
4. Autocompact: The final fallback—calls the model once to compress the entire history into a single paragraph.

Streaming Tool Parallelism: Tools Start Working While the Model Is Still Talking

// StreamingToolExecutor.ts
export class StreamingToolExecutor {
  // Model streams a tool_use block, execution starts immediately
  addTool(block: ToolUseBlock, message: AssistantMessage): void { ... }

  // Concurrency-safe tools run in parallel, write operations are exclusive
  // Results queued in receive order to ensure deterministic output
  async *getRemainingResults(): AsyncGenerator<MessageUpdate> { ... }
}

Refusing to Give Up When Hitting Output Limits

const MAX_OUTPUT_TOKENS_RECOVERY_LIMIT = 3

"Heed these rules well, young wizard. For they are the rules of thinking, and the rules of thinking are the rules of the universe. If ye does not heed these rules, ye will be punished with an entire day of debugging and hair-pulling."

Tool System: 40+ Tools, Zero Inheritance

type ToolDef<T> = {
  name: string
  description: string
  inputSchema: ZodSchema<T>           // Zod v4 for validation + auto-generated JSON Schema
  call(input: T, ctx: ToolUseContext): AsyncGenerator<...>
  isReadOnly(): boolean
  getPermissions(): ToolPermission[]
  renderToolUse?(input: T): ReactNode  // Renders directly to terminal
  getToolUseSummary?(input, result): string  // Summary for context compression
}

• Auto-parses commands into search/read/write categories for permission matching
• Uses sandbox-exec sandbox on macOS, seccomp on Linux
• Auto-backgrounds blocking commands exceeding 15 seconds
• Large outputs stored to disk, only a file path reference given to the model
• Built-in sed command parser—detects sed -i and UI changes from "Bash" to file editing style
• Compound commands like ls && git push are split and evaluated for safety segment by segment

Feature Flag: The Cleanest Feature Gating I've Ever Seen

Compile-Time: Code Physically Disappears

import { feature } from 'bun:bundle'
const voiceModule = feature('VOICE_MODE') ? require('./voice/index.js') : null

Runtime: GrowthBook A/B Testing

const enabled = checkStatsigFeatureGate_CACHED_MAY_BE_STALE(
  'tengu_streaming_tool_execution2'
)

Ablation Experiments: Scientific Method Applied to Product Engineering

if (feature('ABLATION_BASELINE') && process.env.CLAUDE_CODE_ABLATION_BASELINE) {
  for (const k of [
    'CLAUDE_CODE_DISABLE_THINKING',
    'DISABLE_COMPACT',
    'DISABLE_AUTO_COMPACT',
    'CLAUDE_CODE_DISABLE_AUTO_MEMORY',
    'CLAUDE_CODE_DISABLE_BACKGROUND_TASKS',
  ]) {
    process.env[k] ??= '1';
  }
}

Hidden Features: What's in the Source But Not Yet Released

Voice Mode (Codename: Amber Quartz)

• Only supports Claude.ai OAuth authentication (API keys, Bedrock, Vertex don't work)
• Uses dedicated voice_stream endpoint
• Has emergency kill switch: tengu_amber_quartz_disabled
• Comments suggest development is complete, just not yet public

Bridge Mode: Turn Your Computer into Claude's Remote Terminal

Buddy: A Virtual Pet in Your Terminal

// 18 species
export const SPECIES = [
  duck, goose, blob, cat, dragon, octopus, owl, penguin,
  turtle, snail, ghost, axolotl, capybara, cactus, robot,
  rabbit, mushroom, chonk
] as const

// 5 rarity tiers
export const RARITY_WEIGHTS = {
  common: 60, uncommon: 25, rare: 10, epic: 4, legendary: 1,
}

// RPG-style stats
export const STAT_NAMES = ['DEBUGGING', 'PATIENCE', 'CHAOS', 'WISDOM', 'SNARK'] as const

A Secret Hidden in Pet Names

const c = String.fromCharCode
export const duck = c(0x64, 0x75, 0x63, 0x6b) as 'duck'
export const goose = c(0x67, 0x6f, 0x6f, 0x73, 0x65) as 'goose'
export const capybara = c(0x63, 0x61, 0x70, 0x79, 0x62, 0x61, 0x72, 0x61) as 'capybara'

Model Codenames: Two Leaks Complete the Puzzle

// @[MODEL LAUNCH]: Update comment writing for Capybara
// —remove or soften once the model stops over-commenting by default
// @[MODEL LAUNCH]: False-claims mitigation for Capybara v8
// (29-30% FC rate vs v4's 16.7%)

// @[MODEL LAUNCH]: Remove this section when we launch numbat.1

Skill System and Multi-Agent Coordination

Several Easily Overlooked Engineering Details

Cause of the Leak

1. Use whitelist approach for package.json files field—only include what you intend to publish
2. Add CI step to check for .map files in release artifacts
3. Source archive URLs must have authentication—don't leave them naked on CDN
4. Build artifacts and source access control should be managed independently

Final Thoughts