Claude Code CC 2.1.124 and 2.1.126: File Modification Budget Exceeded Reminder, Harness Instructions Update, REPL Awaits Clarification, and Malware Analysis Reminder Removed

Two new releases of Claude Code system prompts shipped: v2.1.124 (+166 tokens) and v2.1.126 (-87 tokens). Here's what changed.

CC 2.1.124: +166 tokens

File modification detection (budget exceeded) reminder

New System Reminder: When a user or linter modifies a file, but the diff is omitted because other modified files already exceeded the snippet budget, the agent now receives a reminder that a file change was detected but not shown. It directs the agent to read the file if the current content is needed.

Harness instructions update

Removed the core-identity function call. Instead, added explicit introductory-line and security-note insertion points before the shared harness instructions. This gives clearer control over how the agent's role and security context are injected.

REPL tool usage and scripting conventions clarification

The system prompt now clarifies that thenable shorthand results (e.g., Promise objects) are only auto-awaited at return time. For inline uses—such as concatenation, template literals, or arguments to another call—you must explicitly await the value first.

Example from the release notes: if using a thenable in a template string, wrap it with await.

CC 2.1.126: -87 tokens

Removed malware analysis reminder

Removed the System Reminder that asked agents to consider whether each file read is malware and to analyze malware without improving or augmenting it. This reduces prompt overhead and avoids unnecessary checks in non-malware contexts.

Who it's for

Developers using Claude Code agents who want to understand token budget impacts, REPL async behavior, and security prompt design.