Reading leaked Claude Code source code

In src/buddy/types.ts, all the species names are hex-encoded:

const c = String.fromCharCode
export const duck = c(0x64,0x75,0x63,0x6b) as 'duck'
export const goose = c(0x67,0x6f,0x6f,0x73,0x65) as 'goose'

All 18 species, spelled out character by character in hexadecimal. Why? The comment explains:

One species name collides with a model-codename canary in excluded-strings.txt. The check greps build output (not source), so runtime-constructing the value keeps the literal out of the bundle while the check stays armed for the actual codename.

So somewhere in Anthropic's build pipeline there's a file called excluded-strings.txt that contains codenames for unreleased models, and a build check that greps the output to make sure none of them leaked into the public build. One of the companion species names happens to match one of these internal codenames. Rather than rename the species, they encoded all of them uniformly in hex so the literal string never appears in the compiled output.

I find this hilarious. Somewhere inside Anthropic, a model is codenamed after an animal that's also a companion species in Claude Code, and the solution is to write "duck" as 0x64,0x75,0x63,0x6b. For the record I don't think the conflicting species is actually "duck" (that would be too simple), but the comment says they encoded all of them uniformly so you can't tell which one it is. Clever.

The commands file has a section of internal-only commands that are hidden in external builds: bughunter, commitPushPr, ctx_viz, goodClaude (which is disabled and hidden, we will never know what it did), ultraplan, ultrareview, teleport, and ant-trace. These exist only in Anthropic's internal build.

There's also a rich set of feature flags for experimental modes: PROACTIVE (autonomous agent), KAIROS (an assistant/brief mode), COORDINATOR_MODE (multi-agent orchestration where Claude spawns worker agents), AGENT_TRIGGERS (cron job scheduling for agents), VOICE_MODE, and BUDDY (the companion pets). The coordinator mode is particularly interesting because it explicitly tells the orchestrating agent: "Never write 'based on your findings' or 'based on the research.' These phrases delegate understanding to the worker instead of doing it yourself." Whoever wrote that has seen too many LLM responses that start with "Based on my findings…"

In src/query.ts, line 24, there's this import:

import {
  logEvent,
  type AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS,
} from 'src/services/analytics/index.js'

This is a TypeScript type and its name is a sentence. Every developer who uses it must type out "I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS" as part of their code. It's a forcing function as you can't accidentally send file paths or code content to analytics without literally typing "I verified this is not code or filepaths."

The /insights command includes a section called "Multi-Clauding (Parallel Sessions)." The function detectMultiClauding() uses a sliding window algorithm to find the pattern: session1 -> session2 -> session1 within a 30-minute window. It counts and reports these as "overlap events."

I think they're tracking when you're running multiple Claude sessions simultaneously and reporting it as a usage metric.

The bash security system (bashSecurity.ts, 2,592 lines) is pure paranoia, and it's fascinating. It validates every shell command against a checklist of attack patterns.

Some highlights of what it checks for:

• Zsh's =cmd expansion, where =curl evil.com expands to /usr/bin/curl evil.com, bypassing permission rules because the parser sees "=curl" as the command name, not "curl"
• zmodload (gateway to zsh/mapfile which enables invisible file I/O)
• Heredoc injection, with a full line-by-line matching algorithm that replicates bash's heredoc-closing behavior
• Shell ANSI-C quoting ($'\x41') because it can encode arbitrary characters
• Process substitution in both directions (<() and >())
• emulate (eval-equivalent arbitrary code execution in zsh)
• ztcp (TCP exfiltration through Zsh builtins)

There's a separate file for destructive command warnings that pattern-matches things like git reset --hard ("may discard uncommitted changes"), rm -rf ("may recursively force-remove files"), DROP TABLE, and kubectl delete ("may delete Kubernetes resources"), each with a human-readable warning explaining what you're about to lose. And all of this is replicated for PowerShell in a separate file that tracks alias hijacking, module loading, and script block cmdlets.

There's a comment "This is really ugly but our current Tool type doesn't make it easy" in the MCP utility code, which feels honest, however I would say the security code is obsessive and thorough in a way that suggests real incidents behind every check, rather than ugly (code is generally ugly, arguably).

src/vim/ contains a full Vim keybinding implementation as a state machine. Not a wrapper around a library. A hand-rolled state machine with INSERT and NORMAL modes, operators (delete, change, yank; 556 lines), motions (h/j/k/l, w/b/e, W/B/E, 0/^/$, G), text objects (words, quotes, brackets, braces), find motions (f/F/t/T with repeat via ;/,), indent/outdent, join lines, replace, toggle case, and dot-repeat. The transitions file (490 lines) handles the full state machine logic.

The motions are pure functions and operators handle smart newline logic. There's a register system with linewise detection. Having went through many Vim (and "evil", in case of Emacs) plugins myself, honestly this is a more complete Vim implementation than most "Vim mode/evil packages" plugins I've used, and it's very impressive.

The query orchestration loop (src/query.ts, 1,729 lines) contains this comment at line 151:

/**
 * The rules of thinking are lengthy and fortuitous. They require plenty
 * of thinking of most long duration and deep meditation for a wizard to
 * wrap one's noggin around.
 *
 * The rules follow:
 * 1. A message that contains a thinking or redacted_thinking block must
 *    be part of a query whose max_thinking_length > 0
 * 2. A thinking block may not be the last message in a block
 * 3. Thinking blocks must be preserved for the duration of an assistant
 *    trajectory
 *
 * Heed these rules well, young wizard. For they are the rules of
 * thinking, and the rules of thinking are the rules of the universe.
 * If ye does not heed these rules, ye will be punished with an entire
 * day of debugging and hair pulling.
 */

There are three rules about how thinking blocks must be handled in the API, and apparently they caused so much suffering that someone chose to document them in medieval English as a warning to future developers. "If ye does not heed these rules, ye will be punished with an entire day of debugging and hair pulling", and the line directly below this comment is ironically const MAX_OUTPUT_TOKENS_RECOVERY_LIMIT = 3. I imagine this constant was born from exactly such a day.

There's a directory called src/buddy/. It implements a companion pet system, complete with species, rarity tiers, stats, ASCII art sprites with idle animations, hats, and eye styles.

Your user ID is hashed (using Mulberry32, a tiny PRNG that has the beautiful comment "good enough for picking ducks") and deterministically rolled into a companion. The species list includes duck, goose, blob, cat, dragon, octopus, owl, penguin, turtle, snail, ghost, axolotl, capybara, cactus, robot, rabbit, mushroom, and "chonk" (see the full species array).

Each companion has a rarity (common 60%, uncommon 25%, rare 10%, epic 4%, legendary 1%), and rarity determines whether your buddy can get a hat. Common buddies always go hatless. Uncommon and above roll from the HATS array, which includes crown, tophat, propeller, halo, wizard hat, beanie, or a "tinyduck", which is apparently a tiny duck sitting on top of your ASCII animal. The array also includes "none" though, so your epic companion might still go bald.

Each companion has five stats: DEBUGGING, PATIENCE, CHAOS, WISDOM, and SNARK. There's always one peak stat and one dump stat, just like D&D character generation. Legendary companions have a floor of 50 in all stats while common ones start at 5.

The architecture is split into "bones" and "soul". Bones (species, rarity, stats, eyes, hat, shininess) are deterministic from your user ID and regenerated every time, so you cannot edit your config file to fake a legendary rarity. The soul (name and personality) is generated once by the model and stored. There's even a shiny boolean with a 1% chance, like shiny Pokémon.

The sprites themselves are defined as 5x12 ASCII art grids with 3 frames of animation each. The cat goes:

   /\_/\
  ( ·   · )
  (  ω  )
  (")_(")

And in frame 2 it wiggles its tail: (")_(")~. The dragon breathes little tildes () in its third frame. The [[https://github.com/chatgptprojects/claude-code/blob/main/src/buddy/sprites.ts#L142-L164][octopus]] alternates between ~/\/\/\/\ and \/\/\/\/ tentacle positions. It's the kind of detail that makes you realize someone on the team was having a genuinely good time.

The companion sits beside the input box and "occasionally comments in a speech bubble." The system prompt instructs Claude not to pretend to be the companion or narrate what it might say, because the companion is handled separately. When the user addresses the companion by name, Claude is told to "stay out of the way: respond in ONE line or less."

The whole thing is behind a feature flag called BUDDY and almost nobody knows it exists.

Some things that I didn't cover in detail but are still worth knowing:

• The loading spinner randomly selects from 186 verbs including "Clauding", "Flibbertigibbeting", "Boondoggling", "Prestidigitating", "Photosynthesizing", "Shenaniganing", "Whatchamacalliting", and "Tomfoolering". When it finishes, it uses past tense verbs (many cooking-themed, like "Sautéed" and "Baked", plus some like "Cogitated" and "Crunched"), so you might see "Sautéed for 12s". You can extend or replace the spinner list in your settings.
• There's a /stickers command that opens your browser to stickermule.com/claudecode. That's the whole command.
• The team memory sync system describes its conflict resolution strategy as "the lesser evil" because local edits overwrite the server version, but the alternative (silently discarding local work) is worse.
• The keyboard parser handles both Kitty and XTerm extended key protocols and has special code paths for SSH tunnels where TERM_PROGRAM isn't forwarded. #Programming