REPL Mode: An Exclusive Workflow for Anthropic's Internal Users

src/tools/REPLTool/constants.ts defines a "REPL mode" — a working mode exclusive to internal Anthropic employees:

// src/tools/REPLTool/constants.ts
export function isReplModeEnabled(): boolean {
  if (isEnvDefinedFalsy(process.env.CLAUDE_CODE_REPL)) return false
  if (isEnvTruthy(process.env.CLAUDE_REPL_MODE)) return true
  return (
    process.env.USER_TYPE === 'ant' &&
    process.env.CLAUDE_CODE_ENTRYPOINT === 'cli'
  )
}

export const REPL_ONLY_TOOLS = new Set([
  FILE_READ_TOOL_NAME,
  FILE_WRITE_TOOL_NAME,
  FILE_EDIT_TOOL_NAME,
  GLOB_TOOL_NAME,
  GREP_TOOL_NAME,
  BASH_TOOL_NAME,
  NOTEBOOK_EDIT_TOOL_NAME,
  AGENT_TOOL_NAME,
])

When REPL mode is enabled, these tools disappear from Claude's direct tool list — Claude can only call them indirectly through the REPL tool. The REPL tool batches multiple operations together, reducing the number of API round-trips. SDK entry points (sdk-ts, sdk-py) never enable REPL mode, because SDK users need to call these tools directly for their automation scripts.