The 29th International Obfuscated C Code Contest (IOCCC) 2025 Winners

The 29th International Obfuscated C Code Contest (IOCCC) 2025 has concluded with a volume and quality of submissions described by organizers as being at "near-historic heights." The contest continues to push the boundaries of the C language, challenging authors to create programs that are functionally correct but intentionally impossible to read.

Notable Winning Entries of IOCCC29

The 2025 winners include a diverse array of complex software implementations compressed into obfuscated C code. Key highlights include:

• GameBoy Emulator (ncw1): Created by Nick Craig-Wood, this entry is noted for its extreme obfuscation, with the source code itself visually resembling a GameBoy.
• OISC Virtual Machine (cable): A 366-byte C program implementing a One Instruction Set Computer (OISC) capable of running Linux and Doom.
• Quine Pong (uellenberg): A combination of a quine (a program that prints its own source code) and a playable game of Pong.
• Patch/Diff Quine (endoh3): A highly resilient entry by Yusuke Endoh.
• Ocean Sound Generator (tompng): An entry recognized for being "most soothing."
• Zoltraak Encoding (yang2): A submission by Don Yang that references the offensive magic from the series Frieren.

Contest Statistics and Trends

Despite a four-year hiatus between 2020 and 2024, the IOCCC has seen a resurgence in participation. The organizers noted that the submission volume for IOCCC29 remained similar to the previous contest (IOCCC28), suggesting a sustained interest in the art of obfuscation.

The "Hat-trick of Hat-tricks"

Three authors achieved the rare feat of winning three separate awards in a single contest:

• Yusuke Endoh: Won for endoh1, endoh2, and endoh3.
• Nick Craig-Wood: Won for ncw1, ncw2, and ncw3.
• Don Yang: Won for yang1, yang2, and yang3.

Global Reach

While winners typically come from established locations, IOCCC29 expanded its geographic footprint with a winning entry from Taiwan by author jingp49.

Evolution of Contest Management

Following the closing of IOCCC28, the organizers implemented a rigorous documentation process for judging, selecting winners, and preparing the website. This effort was intended to improve the overall administration of the contest. Additionally, the IOCCC has integrated more modern workflows, including the use of GitHub pull requests for submitting fixes to winning entries and managing the mkiocccentry repository.

The Role of AI and LLMs in Obfuscation

The intersection of Large Language Models (LLMs) and obfuscated code has become a point of discussion among the community. According to the official guidelines, the IOCCC permits the use of LLMs, acknowledging that authors have a history of using various tools to develop their code.

Community reactions to this are mixed. Some participants argue that LLMs may diminish the meaning of the competition because they can easily convert clear code into obfuscated C and verify its correctness. Others suggest that the potential for LLMs to compete as authors themselves would be a fascinating development.

Looking Ahead to IOCCC30

The organizers plan to open IOCCC30 toward the end of 2026, with the contest expected to close in the first quarter of 2027. Non-winning authors from the 2025 cycle are encouraged to polish their code and resubmit for the 30th anniversary contest, as several 2025 winners were improved versions of previous non-winning entries.

Summary of 2025 Awards

Entry	Award
ayu	IMO award
cable	Best imaginary emulator
cesmoak	Retro space award
diels-grabsch	Best one liner
dogon	Consistently constant award
endoh1	Most likely to dazzle
endoh2	Most likely to shock
endoh3	Most resilient
ferguson	Opposite award
howe	Most likely to invade
jhshrvdp	Most likely to teleport
jingp49	Who won award
kurdyukov	Most likely to count
mattpep	Most obfuscated options
ncw1	Best real emulator
ncw2	Best fractional emulator
ncw3	Best use of Unicode
tompng	Most soothing
uellenberg	Ping pong prize
yang1	Compound prize
yang2	Most magical word
yang3	INABIAF award