It's the last 5 commits, not the full history. Here's what actually gets sent in the system prompt:

  gitStatus: This is the git status at the start of the conversation...
  Current branch: main
  Main branch: main
  Status: (clean)

  Recent commits:
  6578431 chore: Update security contact email (#417)
  0dc71cd chore: Open source readiness fixes (#416)
  ...

Enough for Claude to understand what you've been working on without sending your entire repo history.