CLAUDE_AGENT_SDK_VERSION

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_AGENT_SDK_VERSION is a Claude Code environment variable: Agent SDK version sent in User-Agent header. Present since v2.1.69 or earlier and still present in v2.1.294. It is not in the official reference.

Status	Present in v2.1.294
Added	Present since v2.1.69 or earlier
Category	Agents and subagents
Official docs	Not listed

How to set it

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

export CLAUDE_AGENT_SDK_VERSION=<value>
claude

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

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

Release notes that mention it

83 Undocumented Claude Code Environment Variables (v2.1.19)

Related variables

CLAUDE_AGENT_SDK_CLIENT_APP: Client application name.
CLAUDE_AGENT_SDK_DISABLE_BUILTIN_AGENTS: Disable built-in agent types.
CLAUDE_AGENT_SDK_MCP_NO_PREFIX: Don't prefix MCP tool names with server name.
CLAUDE_AGENT_SDK_DISABLE_MCP_MANIFESTS
CLAUDE_AGENT: Short-form identifier for the current agent, used in inter-agent messaging and log attribution.
CLAUDE_CODE_AGENT: Full agent descriptor passed into a spawned agent process — likely the agent's frontmatter (tools, allowed/disallowed lists, system prompt path) so the child can reconstruct its runtime without re-reading disk.
CLAUDE_CODE_AGENT_COST_STEER: Controls cost-aware behavior for subagent delegation.
CLAUDE_CODE_AGENT_LIST_IN_MESSAGES: An early agent-listing toggle, made obsolete by the Agent View and coordinator surfaces that now own how agents are shown.

Frequently asked questions

What does CLAUDE_AGENT_SDK_VERSION do?

Agent SDK version sent in User-Agent header

Which Claude Code version has CLAUDE_AGENT_SDK_VERSION?

Present since v2.1.69 or earlier and still present in v2.1.294.

How do I set CLAUDE_AGENT_SDK_VERSION?

Export it before starting Claude Code (export CLAUDE_AGENT_SDK_VERSION=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.