Why we made Copilot++

We fell in love with Copilot when it launched back in 2021. It was, and is, a genius idea: Code is inherently low-entropy, which means that as programmers, we're often bottlenecked by keystroke throughput when trying to transfer our ideas into code. Predicting the code to insert next allows us to bypass this bottleneck with a simple Tab.

Something always felt a little bit missing, though. We found ourselves deleting halves of lines to have Copilot rewrite the last half whenever we wanted to do an obvious edit. This required extra keystrokes — the exact thing we were trying to save — and sometimes it just wouldn't even get what we were trying to do, even for edits that felt so obvious to us.

The issue, we realized, is that Copilot tries to solve the wrong problem. It tries to solve the problem of writing completely new code. But as software engineers, most of what we're doing is editing existing code. Simple insertions is the wrong abstraction; edits is the right abstraction. And because of how it's trained, Copilot doesn't exploit the fact that code edits are even lower entropy than code itself.

Copilot++ is our attempt at solving the right problem. Our model is trained on sequences of small diffs, and can see the edits you have made in the last few minutes at inference-time. This makes the model feel much smarter. Copilot++ is also given the ability to actually edit your code, not just predict insertions, so that a single Tab can get you to exactly where you want to be.

As so often happens, it turned out that solving the right problem also came with a few unintentional benefits. Like how you can write pseudocode, hit Tab, and have Copilot++ perfectly translate it into working code. Or how you can press Tab on a lint error to fix the underlying code in one keystroke. Or how, for Vim users, you can fix your code while staying in Normal mode.

Copilot++ is still an early version — for example, we expect latency to be cut in half over the next few months, and we hope to reduce the false-positive rate — but we all already find it really useful, and think you might too. It truly shines when you're in the weeds, coding, and may shine a little bit less bright if you're just trying it out on toy examples, so if you're reading this, we recommend that you go disable your existing autocomplete extension, turn Copilot++ on, and just let yourself experience what it feels like to code with it for a day.

We hope you enjoy.

— The Devs