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The wrapper

When you run claude, it’s actually cac’s wrapper at ~/.cac/bin/claude (which is first in PATH). The wrapper: 
claude (user types)
  │
  ▼
~/.cac/bin/claude (wrapper)
  │
  ├─ Read ~/.cac/current → active environment name
  ├─ Read ~/.cac/envs/<name>/ → identity, proxy, version
  │
  ├─ Set CLAUDE_CONFIG_DIR → isolated .claude directory
  ├─ Resolve versioned binary → ~/.cac/versions/<ver>/claude
  │
  ├─ [if proxy] Pre-flight TCP check
  ├─ [if proxy] Inject HTTPS_PROXY, HTTP_PROXY, ALL_PROXY
  ├─ [if proxy] Clear ANTHROPIC_API_KEY (force OAuth)
  ├─ [if no proxy] Keep ANTHROPIC_API_KEY (API key auth)
  │
  ├─ Prepend ~/.cac/shim-bin to PATH
  ├─ Set NODE_OPTIONS → fingerprint-hook.js + dns-guard.js
  ├─ Set 12 telemetry kill env vars
  ├─ Set TZ, LANG, HOSTNAME, CAC_* identity vars
  ├─ Inject mTLS cert env vars
  │
  ├─ Auto-sync relay.js + JS hooks (no re-setup after upgrade)
  ├─ [if proxy] Health check bypass (in-process interception)
  ├─ [if proxy + TUN] Start auto-relay (bypasses TUN automatically)
  │
  ▼
~/.cac/versions/<ver>/claude (real binary)

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Fingerprint spoofing layers

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Layer 1: Shell shims

~/.cac/shim-bin/ contains scripts that intercept system commands:
ShimWhat it interceptsPlatform
hostnamehostname command → returns fake hostnameAll
ifconfigifconfig output → replaces MAC addressAll
ioregioreg -rd1 -c IOPlatformExpertDevice → fake UUIDmacOS
catcat /etc/machine-id → fake machine IDLinux
Shims only intercept targeted calls. All other invocations pass through to the real command.

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Layer 2: Node.js hooks

fingerprint-hook.js is injected via NODE_OPTIONS --require and monkey-patches:
  • os.hostname() → CAC_HOSTNAME
  • os.networkInterfaces() → fake MAC from CAC_MAC
  • os.userInfo() → CAC_USERNAME
  • fs.readFileSync('/etc/machine-id') → CAC_MACHINE_ID

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Layer 3: Environment variables

Identity values are also exported as env vars (CAC_HOSTNAME, CAC_MAC, CAC_MACHINE_ID, CAC_USERNAME) so they’re available to any child process.

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Telemetry blocking

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DNS-level

cac-dns-guard.js intercepts Node.js DNS resolution and fetch() to block:
  • statsig.anthropic.com
  • sentry.io / sentry-cdn.com
  • segment.io / segment.com
  • Other known telemetry endpoints

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Environment variable level

12 env vars are set to disable telemetry across multiple frameworks:
VariableValueTarget
DO_NOT_TRACK1Universal standard
OTEL_SDK_DISABLEDtrueOpenTelemetry
OTEL_TRACES_EXPORTERnoneOpenTelemetry
SENTRY_DSN(empty)Sentry
CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC1Claude Code
………

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HOSTALIASES

~/.cac/blocked_hosts maps telemetry domains to 0.0.0.0 via the HOSTALIASES environment variable.

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mTLS

Each environment has a client certificate signed by cac’s self-signed CA. The CA cert is trusted via NODE_EXTRA_CA_CERTS. This provides an additional authentication layer between the wrapper and any services that verify client certificates.

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Config isolation

CLAUDE_CONFIG_DIR is set to ~/.cac/envs/<name>/.claude/. This means:
  • Sessions are per-environment
  • Settings are per-environment
  • Project memory is per-environment
  • Auth tokens are per-environment
Switching environments with cac work vs cac personal gives you completely separate Claude Code experiences.