Claude Code Context Compression Data — Fix (2026)

The Error

Context compressed: earlier messages may be incomplete

The Fix

# After seeing this warning, re-read any files critical to your current task
# Tell Claude: "Read src/main.ts and src/config.ts again"
# Store important context that must survive compression:
cat >> CLAUDE.md << 'EOF'
# Current Task State
- Working on: refactoring auth module
- Key file: src/auth/provider.ts
- Approach: extract validateToken into separate utility
EOF

Why This Works

When a conversation exceeds the model’s context window, Claude Code compresses earlier messages to make room. This discards details from the beginning of the session — file contents read earlier, initial instructions, and intermediate decisions. Re-reading files restores that knowledge, and persisting state in CLAUDE.md ensures it survives any future compression cycles.

If That Doesn’t Work

# Start a fresh session with explicit context
claude "Read CLAUDE.md, then continue the auth refactoring task"
# Or use the /compact command proactively before hitting limits
# This gives you control over what gets summarized
# Check conversation length:
# If you've been in one session for 30+ exchanges, start fresh

Long sessions degrade quality progressively. Fresh sessions with good CLAUDE.md context perform better than compressed continuations.

Prevention

Add to your CLAUDE.md:

For multi-step tasks, record current progress and key decisions in CLAUDE.md after each major step. Keep sessions focused on single objectives. Start new sessions rather than extending conversations beyond 25-30 exchanges.

This fix also applies if you see these related error messages:

  • ContextWindowExceeded: input exceeds maximum context length
  • Error: message content too large
  • TokenLimitExceeded: reduce input size
  • TokenLimitExceeded: max tokens reached
  • Error: output truncated at max_tokens

Frequently Asked Questions

What is the context window limit?

Claude’s context window is 200,000 tokens. This includes system prompts, conversation history, file contents read during the session, and tool results. When the total exceeds this limit, Claude Code must compress or drop earlier context.

How does context compression work?

When approaching the context limit, Claude Code summarizes earlier messages to free space for new content. This compression is lossy — specific code snippets and exact line numbers from early in the conversation may be approximated. Starting a fresh conversation avoids compression artifacts.

How do I work with large codebases without exceeding the context?

Be specific about which files to read. Instead of asking Claude Code to ‘understand the whole codebase,’ point it to the specific files relevant to your task. Use the Glob and Grep tools to find relevant code before reading it.

What causes token count mismatches?

Token counts are estimated before sending a request and precisely calculated on the server. The estimation uses a fast local tokenizer that may differ slightly from the server’s tokenizer. Small discrepancies (1-3%) are normal and do not affect functionality.

Estimate usage → Calculate your token consumption with our Token Estimator.

Try it: Paste your error into our Error Diagnostic for an instant fix.

Implementation Details

When working with this in Claude Code, pay attention to these practical details:

Project configuration. Add specific instructions to your CLAUDE.md file describing how your project handles this area. Include file paths, naming conventions, and any patterns that differ from common defaults. Claude Code reads CLAUDE.md at the start of every session and uses it to guide all operations.

Testing the setup. After configuration, verify everything works by running a simple test task. Ask Claude Code to perform a read-only operation first (like listing files or reading a config) before moving to write operations. This confirms that permissions, paths, and tools are all correctly configured.

Monitoring and iteration. Track your results over several sessions. If Claude Code consistently makes the same mistake, the fix is usually a more specific CLAUDE.md instruction. If it makes different mistakes each time, the issue is likely in the project setup or toolchain configuration.

Troubleshooting Checklist

When something does not work as expected, check these items in order:

  1. CLAUDE.md exists at the project root — run ls -la CLAUDE.md to verify
  2. Node.js version is 18+ — run node --version to check
  3. API key is set — run echo $ANTHROPIC_API_KEY | head -c 10 to verify (shows first 10 characters only)
  4. Disk space is available — run df -h . to check
  5. Network can reach the API — run curl -s -o /dev/null -w "%{http_code}" https://api.anthropic.com (should return 401 without auth, meaning the server is reachable)
  6. No conflicting processes — run ps aux | grep claude | grep -v grep to check for stale sessions