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Overview

Claude Code uses build-time feature flags via Bun’s bundler API. Flags are evaluated by a feature() function at bundle time — code paths behind disabled flags are dead-code-eliminated from the distributed package before it reaches users. 
if (feature('VOICE_MODE')) {
  // this entire block is removed from public builds when the flag is off
  initializeVoiceMode()
}

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Internal vs external builds

The codebase distinguishes between Anthropic-internal builds and the public npm package using a sentinel string comparison: 
if ("external" !== 'ant' && isBeingDebugged()) {
  process.exit(1)
}
When the build target is set to 'ant', the expression "external" !== 'ant' evaluates to false, allowing internal tooling (debuggers, test harnesses) to run without triggering the anti-debugging guard. In public builds the expression is always true. Feature flags that are internal-only are similarly gated: the feature() call returns false in public builds, and the bundler removes the enclosed code entirely.

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Feature flags

FlagDescription
COORDINATOR_MODEMulti-agent orchestration mode
KAIROSAssistant/proactive agent mode
VOICE_MODEVoice input via speech-to-text
BRIDGE_MODEMobile/web remote control bridge
SSH_REMOTESSH remote execution
DIRECT_CONNECTDirect server connections
ULTRAPLANAdvanced planning mode
BUDDYCompanion sprite Easter egg
FORK_SUBAGENTAgent forking capability
TRANSCRIPT_CLASSIFIERAuto-mode safety classifier
EXPERIMENTAL_SKILL_SEARCHSkill discovery feature
WEB_BROWSER_TOOLBrowser automation tool
These flags are compiled at build time. You cannot enable or disable them at runtime — their values are fixed in the distributed package you install.

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Internal codenames

The source code references several internal project codenames. These appear in file names, analytics event prefixes, and comments.
CodenameMeaning
TenguAnalytics event prefix (tengu_*) — Claude Code’s internal project name
KairosAssistant/proactive agent mode
FennecEarlier Claude model variant, now migrated to Opus
LodestoneDeep link / URL protocol handler
TungstenExperimental tool type
WalrusReactive compact feature
TorchExperimental command
UltraplanAdvanced multi-step planning mode
GroveUI component system
BuddyAnimated companion sprite (Easter egg)
Codenames surface occasionally in error messages, log output, and settings keys. For example, analytics events are prefixed with tengu_ (e.g. tengu_sonnet45_to_46_migration), and the Fennec model alias is handled by the migrateFennecToOpus migration.

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