CLAUDE_CODE_MCP_INSTR_DELTA

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_CODE_MCP_INSTR_DELTA is a Claude Code environment variable: Delta/incremental MCP instruction updates. Instead of sending full MCP server instructions every turn, this likely enables sending only changes — reducing overhead for sessions with many MCP servers. Removed in v2.1.91, so current releases ignore it. It is not in the official reference.

Status	Removed in v2.1.91
Added	Added in v2.1.70
Category	MCP
Official docs	Not listed

How to set it

For one session, export it in the shell that starts Claude Code:

export CLAUDE_CODE_MCP_INSTR_DELTA=<value>
claude

To apply it to every session, add it to the env object of a settings file:

// ~/.claude/settings.json
{
  "env": {
    "CLAUDE_CODE_MCP_INSTR_DELTA": "<value>"
  }
}

Release notes that mention it

Claude Code v2.1.70 — 3 New Environment Variables and 1 Removed

Related variables

CLAUDE_CODE_ENABLE_REFRESH_MCP_TOOLS: Enables an on-demand MCP-tool refresh capability, grouped with CLAUDE_CODE_ENABLE_TASKS and CLAUDE_CODE_ENABLE_REMOTE_RECAP.
CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH
CLAUDE_CODE_MCP_ALLOWLIST_ENV: Specifies an allowlist of environment variables that MCP servers can access.
CLAUDE_CODE_MCP_AUTO_BACKGROUND_MS
CLAUDE_CODE_MCP_SERVER_NAME: Added in v2.1.85 to identify which MCP server a helper process was acting on behalf of.
CLAUDE_CODE_MCP_STARTUP_WAIT_MS
ENABLE_CLAUDEAI_MCP_SERVERS: Enable Claude.ai-hosted MCP servers.
ENABLE_MCP_LARGE_OUTPUT_FILES: Enable large output files for MCP.

Frequently asked questions

What does CLAUDE_CODE_MCP_INSTR_DELTA do?

Delta/incremental MCP instruction updates. Instead of sending full MCP server instructions every turn, this likely enables sending only changes — reducing overhead for sessions with many MCP servers.

Which Claude Code version has CLAUDE_CODE_MCP_INSTR_DELTA?

Removed in v2.1.91, so current releases ignore it.

How do I set CLAUDE_CODE_MCP_INSTR_DELTA?

Export it before starting Claude Code (export CLAUDE_CODE_MCP_INSTR_DELTA=value), or add it to the "env" object in ~/.claude/settings.json to apply it to every session.

All variables, searchable: Claude Code environment variables.