https://github.com/btucker/graftty

Nov 2024: Don’t dismiss this; it may be the next platform shift. But the actual questions are still unsettled: scaling, usefulness, deployment, and business model.

May 2025: The model layer is already showing signs of commoditization, so the important question shifts toward deployment: products, use cases, UX, errors, and enterprise adoption.

Nov 2025: The capital cycle has become the story: everyone is spending because missing the platform shift is worse than overbuilding, but there is still no clarity on product shape, moats, or value capture. That creates bubble-like dynamics.

May 2026: Provisional thesis: models look likely to become infrastructure, while value probably moves up-stack into apps, workflows, product, proprietary data/context, GTM, and new questions made possible by cheap automation. But he is still explicitly calling this provisional.

It was a great reminder for a bunch of hotshot underclassmen that there were so many skills we all had yet to develop.

Unfortunately, I found the small context window makes the utility pretty limited.

Playground here: https://btucker.github.io/selkie/

One of the cool features is it can use kitty to output diagrams direct to the terminal (if kitty is supported like in ghostty).

I'm planning to blog about the whole process soon.

ETA: used Claude Code to reverse engineer it:

   Insight ─────────────────────────────────────

  Claude.app VM Architecture:
  1. Uses Apple's Virtualization.framework (only on ARM64/Apple Silicon, macOS 13+)
  2. Communication is via VirtioSocket (not stdio pipes directly to host)
  3. The VM runs a full Linux system with EFI/GRUB boot

  ─────────────────────────────────────────────────

        ┌─────────────────────────────────────────────────────────────────────────────────┐
        │  macOS Host                                                                     │
        │                                                                                 │
        │  Claude Desktop App (Electron + Swift native bindings)                          │
        │      │                                                                          │
        │      ├─ @anthropic-ai/claude-swift (swift_addon.node)                           │
        │      │   └─ Links: Virtualization.framework (ARM64 only, macOS 13+)            │
        │      │                                                                          │
        │      ↓ Creates/Starts VM via VZVirtualMachine                                   │
        │                                                                                 │
        │  ┌──────────────────────────────────────────────────────────────────────────┐  │
        │  │  Linux VM (claudevm.bundle)                                              │  │
        │  │                                                                          │  │
        │  │  ┌────────────────────────────────────────────────────────────────────┐  │  │
        │  │  │  Bubblewrap Sandbox (bwrap)                                        │  │  │
        │  │  │  - Network namespace isolation (--unshare-net)                     │  │  │
        │  │  │  - PID namespace isolation (--unshare-pid)                         │  │  │
        │  │  │  - Seccomp filtering (unix-block.bpf)                              │  │  │
        │  │  │                                                                    │  │  │
        │  │  │  ┌──────────────────────────────────────────────────────────────┐  │  │  │
        │  │  │  │  /usr/local/bin/claude                                       │  │  │  │
        │  │  │  │  (Claude Code SDK - 213MB ARM64 ELF binary)                  │  │  │  │
        │  │  │  │                                                              │  │  │  │
        │  │  │  │  --input-format stream-json                                  │  │  │  │
        │  │  │  │  --output-format stream-json                                 │  │  │  │
        │  │  │  │  --model claude-opus-4-5-20251101                            │  │  │  │
        │  │  │  └──────────────────────────────────────────────────────────────┘  │  │  │
        │  │  │       ↑↓ stdio (JSON-RPC)                                          │  │  │
        │  │  │                                                                    │  │  │
        │  │  │  socat proxies:                                                    │  │  │
        │  │  │  - TCP:3128 → /tmp/claude-http-*.sock (HTTP proxy)                │  │  │
        │  │  │  - TCP:1080 → /tmp/claude-socks-*.sock (SOCKS proxy)              │  │  │
        │  │  └────────────────────────────────────────────────────────────────────┘  │  │
        │  │                                                                          │  │
        │  └──────────────────────────────────────────────────────────────────────────┘  │
        │           ↕ VirtioSocket (RPC)                                                 │
        │      ClaudeVMDaemonRPCClient.swift                                             │
        │           ↕                                                                    │
        │      Node.js IPC layer                                                         │
        └─────────────────────────────────────────────────────────────────────────────────┘

ComponentDetailsKernelLinux 6.8.0-90-generic aarch64 (Ubuntu PREEMPT_DYNAMIC)OSUbuntu 22.04.5 LTS (Jammy Jellyfish)HostnameclaudeCPU4 cores, Apple Silicon (virtualized), 48 BogoMIPSRAM3.8 GB total (~620MB used at idle)SwapNone

Storage Layout

DeviceSizeTypeMount PointPurpose/dev/nvme0n1p19.6 GBext4/Root filesystem (rootfs.img)/dev/nvme0n1p1598 MBvfat/boot/efiEFI boot partition/dev/nvme1n19.8 GBext4/sessionsSession data (sessiondata.img)virtiofs-virtiofs/mnt/.virtiofs-root/shared/...Host filesystem access

Filesystem Mounts (User Perspective)

        /sessions/gallant-vigilant-lamport/
        ├── mnt/
        │   ├── claude-cowork/     → Your selected folder (virtiofs + bindfs)
        │   ├── .claude/           → ~/.claude config (bindfs, rw)
        │   ├── .skills/           → Skills/plugins (bindfs, ro)
        │   └── uploads/           → Uploaded files (bindfs)
        └── tmp/                   → Session temp files
        
        Session User
        A dedicated user is created per session with a Docker-style random name:
        User: gallant-vigilant-lamport
        UID:  1001
        Home: /sessions/gallant-vigilant-lamport
        Process Tree
        PID 1: bwrap (bubblewrap sandbox)
        └── bash (shell wrapper)
            ├── socat TCP:3128 → unix socket (HTTP proxy)
            ├── socat TCP:1080 → unix socket (SOCKS proxy)
            └── /usr/local/bin/claude (Claude Code SDK)
                └── bash (tool execution shells)

        Security Layers

        Apple Virtualization.framework - Hardware-level VM isolation
        Bubblewrap (bwrap) - Linux container/sandbox

        --unshare-net - No direct network access
        --unshare-pid - Isolated PID namespace
        --ro-bind / / - Read-only root (with selective rw binds)


        Seccomp - System call filtering (unix-block.bpf)
        Network Isolation - All traffic via proxied unix sockets

        Network Architecture
        ┌─────────────────────────────────────────────────────────────┐
        │  Inside Sandbox                                             │
        │                                                             │
        │  claude process                                             │
        │      │                                                      │
        │      ↓ HTTP/HTTPS requests                                  │
        │  localhost:3128 (HTTP proxy via env vars)                   │
        │      │                                                      │
        │      ↓                                                      │
        │  socat → /tmp/claude-http-*.sock ─────────┐                │
        │                                            │                │
        │  localhost:1080 (SOCKS proxy)              │                │
        │      │                                     │                │
        │      ↓                                     │                │
        │  socat → /tmp/claude-socks-*.sock ────────┤                │
        └───────────────────────────────────────────┼────────────────┘
                                                    │
                                VirtioSocket ←──────┘
                                                    │
        ┌───────────────────────────────────────────┼────────────────┐
        │  Host (macOS)                             │                │
        │                                           ↓                │
        │                              Claude Desktop App            │
        │                                           │                │
        │                                           ↓                │
        │                                    Internet                │
        └─────────────────────────────────────────────────────────────┘
        Key insight: The VM has only a loopback interface (lo). No eth0, no bridge. All external network access is tunneled through unix sockets that cross the VM boundary via VirtioSocket.


  Communication Flow

  From the logs and symbols:

  1. VM Start: Swift calls VZVirtualMachine.start() with EFI boot
  2. Guest Ready: VM guest connects (takes ~6 seconds)
  3. SDK Install: Copies /usr/local/bin/claude into VM
  4. Process Spawn: RPC call to spawn /usr/local/bin/claude with args

  The spawn command shows the actual invocation:
  /usr/local/bin/claude --output-format stream-json --verbose \
    --input-format stream-json --model claude-opus-4-5-20251101 \
    --permission-prompt-tool stdio --mcp-config {...}

Great Engineer + AI = Great Engineer++ (Where a great engineer isn't just someone who is a great coder, they also are a great communicator & collaborator, and love to learn)

Good Engineer + AI = Good Engineer

OK Engineer + AI = Mediocre Engineer

Interesting you're getting such slow speeds. Ask them if a tech can stop by and troubleshoot with you.