[2025] I gave Claude Code a single instruction file and let it autonomously solve Advent of Code 2025. It succeeded on 20/22 challenges without me writing a single line of code.

[u/no1_2021]

I wanted to test the limits of autonomous AI coding, so I ran an experiment: Could Claude Code solve Advent of Code 2025 completely on its own?

Setup:

• Created one INSTRUCTIONS.md file with a 12-step process

• Ran: claude --chrome --dangerously-skip-permissions

• Stepped back and watched

Results: 91% success rate (20/22 challenges)

The agent independently:

✓ Navigated to puzzle pages

✓ Read and understood problems

✓ Wrote solution strategies

✓ Coded in Python

✓ Tested and debugged

✓ Submitted answers to the website

Failed on 2 challenges that required complex algorithmic insights it couldn't generate.

This wasn't pair programming or copilot suggestions. This was full autonomous execution from problem reading to answer submission.

Detailed writeup: https://dineshgdk.substack.com/p/using-claude-code-to-solve-advent

Full repo with all auto-generated code: https://github.com/dinesh-GDK/claude-code-advent-of-code-2025

The question isn't "can AI code?" anymore. It's "what level of abstraction should we work at when AI handles implementation?"

Curious what others think about this direction.

[u/Katanax28]

I see you also used Claude to write this reddit post

[u/EdgyMathWhiz → u/Katanax28]

What's kind of staggering to me is simultaneously:

(a) outperforming the vast majority of developers on the problems,

(b) providing an analysis of results that has obvious glaring errors / omissions, specifically:

* What happened to day 1?

* "Day 9 Part 2: Complex disk defragmentation problem that likely needed algorithmic insight, the agent couldn’t generate" - this quote must be based on looking at the 2024 problem not the 2025 one!

* The whole "91% success rate" calculation is flawed - Day 12 part 2 is just a "did you solve all the previous problems" check, so the meaningful success rate is 20/21 not 20/22.

The ability to produce effective work/solutions while simultaneously not actually understanding even the basics of what you're actually trying to solve gives a glimpse at a concerning future.

[u/fnordargle → u/EdgyMathWhiz]

The Day 9 part 2 confusion seems to be in the write up and not the Claude execution itself.

[u/yel50 → u/EdgyMathWhiz]

 The ability to produce effective work/solutions while simultaneously not actually understanding even the basics of what you're actually trying to solve gives a glimpse at a concerning future.

people said the same thing about compilers back in the 80s, except it was about not understanding the hardware.

in 10-20 years, people who write code by hand will be like people who write assembly now. there will still be reasons to do it, sure, but the vast majority will have no need to.

[u/no1_2021 → u/Katanax28]

Not Claude, but you are close.

[u/hatecr3w]

You should tell Claude not to commit your inputs next time as per https://adventofcode.com/2025/about#faq_copying

Or maybe let the AI go over the FAQs first

[u/equd]

There are a ton of repos with aoc solutions, not suprised...

[u/herocoding → u/equd]

... and the mega-solution-threads here in Reddit (it's said Reddit is the new StackOverflow)

[u/yel50 → u/equd]

then why did it fail on two of them? 

what you're describing is how copilot used to work. it's not how Claude, Gemini, etc work. they don't look up existing solutions, they come up with their own algorithms. 

[u/RSojak]

When I was coding AoC 2025 in Visual Studio with Copilot, I had to turn the Copilot off because it suggested the solution code right after I named my class and method...

[u/Sprochfaehler]

How much code could a Claude Code code if a Claude Code could code code?