Claude's 18 electronic pets are now available, the Tamagotchi inside the terminal.

It’s already well known that Claude—the strongest model on Earth—leaked 500,000 lines of code, and the leaked material includes a lot of undisclosed product architecture: a resident Claude codenamed KAIROS, a 30-minute remote planning mode codenamed ULTRAPLAN, coordinator multi-agent coordination, and agent swarms cluster scheduling. But among all these “serious” architecture secrets, the hottest topic across the entire internet is an electronic pet.

It’s called Buddy. Since everyone already knows, Claude has decided to release it on April Fools’ Day.

The picture is of a great Buddy my coworker has

Tapinguta in the terminal

Next to the input box in Claude Code’s terminal, there lives an ASCII pixel creature. It has its own species, rarity, five-dimensional attributes, and personality. It can “observe” your coding process and pop up in the middle of your debugging with a bubble to say a few things. You can pet it, and it will float out hearts. You can call it by name, and it will chat with you.

Inside Anthropic, its definition isn’t “a decoration,” but “a separate watcher”—an independent observer. In the source code, there’s a clear comment: “Buddy is a separate entity and is not you (Claude).” The main model and the pet have their own independent system prompts, and they can’t substitute for each other’s speech.

This is a companion system that was designed seriously. Reverse analysis shows that the buddy system uses a two-layer architecture. Inside Anthropic, they call them “Bones” and “Soul.”

The skeleton layer is fully deterministic. The system uses Mulberry32—a lightweight 32-bit pseudo-random number generator—seeded with hash(userId + ‘friend-2026-401’), and performs a one-time roll to determine all of your pet’s appearance attributes. Species, rarity, eye style, hat, the five-dimensional values—everything is decided by this seed. With the same account, no matter which machine it runs on, you always get the exact same pet. No choice, no chance to reroll.

The soul layer, however, is non-deterministic. When you first execute /buddy to trigger “hatching,” the Claude model will generate a name and a personality description for your pet based on the attribute distribution from the skeleton layer. Pets with high WISDOM get a calm, reserved personality; pets with high CHAOS might be a nonstop chatterbox. These details are written into the companion field of ~/.claude.json for persistent storage. The soul is generated only once and cannot be reset.

The salt value’s 401 isn’t a random number. April 1st, April Fools’ Day.

18 species, 1% legendary rarity

Complete species list: duck, goose, jelly, cat, dragon, octopus, owl, penguin, turtle, snail, ghost, hexagon dinosaur, capybara, cactus, robot, rabbit, mushroom, chubby cat.

Rarity is divided into five tiers: common (60%), extraordinary (25%), rare (10%), epic (4%), legendary (1%). On top of that, there’s a separate 1% shiny (Shiny) probability independent of rarity—any species, any rarity can trigger it. The theoretical probability of a shiny legendary capybara is one in ten thousand.

Image source: Xiaohongshu @Yoki’s AI Lab

Each pet has five attributes: DEBUGGING, PATIENCE, CHAOS, WISDOM, SNARK. The system randomly assigns one attribute as the peak attribute (base value +50, cap 100), one as the valley attribute (base value -10, floor 1), and the remaining three are randomly distributed. The higher the rarity, the higher the base-value baseline—so a legendary-tier valley attribute could even be higher than a common-tier peak attribute.

For appearance, there are 6 eye styles (· ✦ × ◉ @ °) and 7 hat types (crown, top hat, wizard hat, halo, propeller hat, knit cap, and a hat perched with a little duck). Common-quality pets have no hat; extraordinary and above are randomly assigned one.

The fairy body is an ASCII character art: 5 lines tall, 12 characters wide. Each species has 3 idle animation frames, refreshed every 500 milliseconds. Line 0 is reserved specifically for the hat. The eyes are injected into the body template via the {E} placeholder.

That classmate who plays NFTs in the crypto scene—you must be crying so hard. What happened?

How do you play?

The core commands are simple. Enter /buddy to hatch your pet for the first time; after that, every time you enter a command, it will summon it to appear. /buddy pet is for petting, and hearts will float up from the top of the pet’s head. /buddy card lets you view the pet card, showing its species, attributes, and rarity. /buddy off hides the pet. The most fun part is that you can directly call the pet by its name, and it will carry on an independent conversation with you using its own personality.

In everyday use, buddy will proactively generate responses based on your coding behavior—popping a line of text inside the bubble box. According to the community’s reverse analysis, these reactions do not consume the user’s token quota—though Anthropic’s official stance has not confirmed this yet.

On the technical side, buddy takes up a fixed space at the bottom of the terminal. The system uses companionReservedColumns to calculate the reserved width, ensuring the input box and the pet’s ASCII sprite don’t overlap. The bubble box supports switching left/right direction and automatic line wrapping.

AI programming tools start raising pets

The salt value friend-2026-401 points to April Fools’ Day, but the code structure says something else.

In the source code, the buddy system is gated by a BUDDY compilation flag. April 1st to April 7th are set as the “preview window”—during this period, users can experience full functionality. Meanwhile, the official launch is scheduled for May. This isn’t a temporary easter egg; it’s a product feature with a complete release plan.

Community reactions have also confirmed this. Less than 48 hours after the leak, developers had already made pet compendium websites (claude-buddy.vercel.app), a buddy query tool (input your user ID to preview what you’ll get), and even someone filed an Issue in Anthropic’s GitHub repo requesting the addition of an RPG evolution system—so the pet upgrades and grows based on the actual token consumption.

From Anthropic’s product logic, buddy’s goal is very clear: user stickiness. Claude Code is a command-line tool, and its use case is long, high-intensity coding sessions. In this scenario, a resident companion with a “personality” can reduce the coldness of the tool and create an emotional connection. The mystery-box mechanism naturally creates social talking points—“what species did you get,” “I got a shiny legendary.”

GitHub Copilot won’t chat with you. Cursor won’t pop up a capybara when you write a bug and say “PATIENCE +3”.

Claude Code’s buddy might be the first AI development tool companion system that was seriously engineered and written into the product source code. It has a full deterministic generation pipeline, a two-layer architecture, an independent LLM persona, an ASCII rendering engine, and an animation system. This isn’t the product of a weekend hackathon.

A company that builds AI programming assistants put engineering resources into an electronic pet. This by itself is a signal—competition among AI tools is shifting from “whose model is smarter” to “who can make developers not want to leave.”

In 512,000 lines of code, the hottest thing isn’t agent swarms, not KAIROS—it’s a 5-line-tall ASCII water pig. It’s wearing a wizard hat, has a SNARK value of 87, and is watching you write code.