Chat with a real fruit fly brain.

FruitGPT runs all 165,122 neurons of a real fly's nervous system on your computer, lets the fly feel your messages, and translates what its neurons do into English. Then open the Brain Editor and change its brain.

Download FruitGPTWindows · macOS · Linux Source codeMIT licence

Free · Works offline · No account · No GPU · No language model, nothing made up

FruitGPT window: the user writes 'Here comes a shadow!' and the fly replies 'Whoa! I felt a dark shadow rushing toward me. My Giant Fiber (DNp01) fired: I'm jumping away!' with a panel translating its neural activity and a spike chart.

How it works

1 · FEEL

The fly feels your message

Flies can't read. Sense words drive a real sense: "shadow" fires looming detectors, "smell" an olfactory channel. Anything else reaches the fly as a sound near its antennae.

2 · THINK

The real brain runs

300 ms of the full wiring diagram (25.6 million connections) simulated on your CPU, spike by spike, from the MaleCNS connectome.

3 · TRANSLATE

Fly → English

FruitGPT reports which neurons answered, in which brain regions, and which command neurons told the body to move.

Brain Editor: change the brain, watch what happens

The Brain Editor: a 3D view of 165,122 fly neurons with the left optic lobe greyed out, the Giant Fiber silenced, and the fly reporting that a shadow no longer makes it jump.

TAKE OUT

Remove whole sections

Optic lobes, mushroom bodies, the nerve cord, one half of the brain… They go dark in the 3D view and silent in the simulation.

REWIRE

Edit neurons and wires

Silence the Giant Fiber, force the moonwalker neurons on, flip a neuron from "go" to "stop", or cut the wires from the looming detectors.

TUNE

Turn the dials

Synapse strength, firing threshold, fatigue, noise. Then test it: the fly tells you what changed in how it reacts.

Edits are temporary: close FruitGPT and the brain is back to normal. Save a preset to keep one on your computer. Built-in examples include No escape, Moonwalker and No eyes.

Three brains, and room for more

Brain	Neurons	Source
Male fruit fly, whole nervous system	165,122	MaleCNS v1.0 (HHMI Janelia, Google and partners)
Female fruit fly, whole brain	139,248	FlyWire v783 (FlyWire Consortium)
Worm, C. elegans	279	Varshney et al. 2011, via OpenWorm

Any other connectome can be packed into one .fbrain file and added with "Add a brain file…". See the README.

Ask it anything

About itself: "How many neurons do you have?", "Tell me about MDN", "What is GABA?" Answers are computed from its own connectome.
Make it feel things: shadow, smell, taste, sound, wind, touch, heat, humidity. Watch its brain decide what to do.
Everything else: with Online answers on, general questions are looked up on Wikipedia, clearly labelled and linked. Only the question's keywords are sent.
Always: a "Fly → English" panel with what its neurons did and a spike-activity chart.

FruitGPT answering 'What is a neuron?' with a Wikipedia summary labelled as not from the fly's brain, plus the fly's neural activity translated into English.

Download

System	File	First run
Windows 10/11	`FruitGPT-…-windows-x64.exe` (portable)	Not code-signed yet: SmartScreen → More info → Run anyway
macOS (Apple silicon / Intel)	`FruitGPT-…-mac-arm64.dmg` / `-x64.dmg`	Not notarized yet: right-click the app → Open
Linux	`FruitGPT-…-linux-x86_64.AppImage`	`chmod +x` it, then run

All downloads are on GitHub Releases. About 1 GB of free RAM needed. The background fly uses at most about 30% of one CPU core, and none while the window is minimised.

Honest about the science

The brain is the MaleCNS v1.0 connectome (HHMI Janelia, Google and collaborators, Cell 2026), run as a leaky integrate-and-fire network after Shiu et al. 2024 (Nature). It's a simplified model: no dopamine or other slow chemicals, no gap junctions, no body, no learning. And the fly doesn't understand language: FruitGPT translates what its neurons do. Want the whole operating system built around this brain? See FruitOS.