[BUG] `CLAUDE_SESSION_ID` not found in env

[BowTiedRadone]

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

CLAUDE_SESSION_ID seems to be no longer available in the main agent context.

❯ What is CLAUDE_SESSION_ID?                                                                                                                                                        
                                               
⏺ CLAUDE_SESSION_ID is a built-in environment variable provided by Claude Code that contains a unique identifier for the current conversation/session. It's a UUID that stays       
  constant throughout a single conversation but changes when a new conversation starts.                                                                                                                                                                                
                                                                                                                                                                                  
  You can see its current value:                                                                                                                                                    

⏺ Bash(echo $CLAUDE_SESSION_ID)
  ⎿  (No content)
                                                                                                                                                                                    
⏺ Interesting — it's empty in this shell context. Let me check how it's typically available:                                                                                        
                                                                                                                                                                                    
⏺ Bash(env | grep -i claude)                                                                                                                                                        
  ⎿  CLAUDE_CODE_SSE_PORT=32421
     CLAUDE_CODE_ENTRYPOINT=cli                                                                                                                                                     
     CLAUDECODE=1 

What Should Happen?

CLAUDE_SESSION_ID should be exported and available.

Error Messages/Logs

Steps to Reproduce

1. start claude: claude
2. ask for CLAUDE_SESSION_ID

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

2.1.37

Platform

Other

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

No response

[techjoec]

Workaround: Get your session ID via a SessionStart hook

Claude Code hooks receive session_id in their stdin JSON — you just need to feed it back. This gives you $CLAUDE_CODE_SESSION_ID in both the conversation context and the shell environment.

---

Setup (2 files)

Step 1 — Create the hook script

Save this as ~/.local/bin/claude-session-id-hook (or anywhere on your PATH):

#!/usr/bin/env bash
INPUT=$(cat)
SESSION_ID=$(echo "$INPUT" | jq -r '.session_id // empty')

# Inject into conversation context so the model can see it
jq -n --arg ctx "CLAUDE_CODE_SESSION_ID=$SESSION_ID" \
    '{ hookSpecificOutput: { hookEventName: "SessionStart", additionalContext: $ctx } }'

# Inject into shell environment so Bash tool calls can use it
# Guard: each session gets its own env file — skip if already written (resume/continue)
if [ -n "$CLAUDE_ENV_FILE" ] && ! grep -q "CLAUDE_CODE_SESSION_ID" "$CLAUDE_ENV_FILE" 2>/dev/null; then
    echo "export CLAUDE_CODE_SESSION_ID=\"$SESSION_ID\"" > "$CLAUDE_ENV_FILE"
fi

Then: chmod +x ~/.local/bin/claude-session-id-hook

Step 2 — Register the hook

Add to your ~/.claude/settings.json (merge into existing hooks if you have them):

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "claude-session-id-hook",
            "timeout": 5000
          }
        ]
      }
    ]
  }
}

---

Verify it works

Start a new Claude Code session, then run:

!echo $CLAUDE_CODE_SESSION_ID

You should get a UUID like a4b692e2-9095-43e4-849d-385e9e454782.

You can also ask Claude: "What is your CLAUDE_CODE_SESSION_ID from your system reminder?" — it will be able to read it directly from its context.

---

How it works

Channel	Mechanism	Available to
Conversation context	hookSpecificOutput.additionalContext	The model (system reminder)
Shell environment	$CLAUDE_ENV_FILE	Bash tool calls (echo $CLAUDE_CODE_SESSION_ID)

Edge cases handled

Scenario	Behavior
Resumed/continued session	Same env file path — grep guard skips the write
Forked session	New session ID, new env file — writes fresh
Parallel sessions	Each session invokes its own hook with its own stdin JSON
Subagents	Get the session ID via their parent's context (add a SubagentStart hook entry with the same script if you want it explicitly)

Requirements

• jq installed
• Claude Code with hooks support

[dpearson2699]

Confirmed this is still an bug on CC version 2.1.52

[github-actions]

Closing for now — inactive for too long. Please open a new issue if this is still relevant.