2025 was an eventful year of progress. I doubled down on my health, had some pleasant career surprises, and my wife and I made time for two vacations.

Reviewing my 2025 Goals

✅ Write 6 substantive pieces: Before 2023, most of my technical writing focused on RecSys and Search. In 2023 - 2024, this shifted towards applying LLMs. In 2024, I worked to bridge these two interests, starting with a deep dive on Improving RecSys & Search in the Age of LLMs. I then followed up with a technical walkthrough on finetuning an LLM-RecSys Hybrid for Steerable Recs with Semantic IDs. The deep dive was well received and led to an invitation from the AI Engineer World’s Fair to host the first-ever LLM × RecSys track.

The other major themes in my writing were evals—an industry where we still have much to learn and do as an industry—as well as general career and leadership advice.

• Improving Recommendation Systems & Search in the Age of LLMs
• Training an LLM-RecSys Hybrid for Steerable Recs with Semantic IDs
• Evaluating Long-Context Question & Answer Systems
• Product Evals in Three Simple Steps
• Advice for New Principal Tech ICs (i.e., Notes to Myself)
• Frequently Asked Questions about My Writing Process

✅ Prototype 4 apps in public: One of my all-time favorites is AI Reading Club (ARC; how it’s built). Inspired by Karpathy’s tweet, I built ARC to help people get more out of reading. I wasn’t satisfied with existing ideas, like uploading PDFs to a chatbot, because I thought they neglected the reading experience of the original text. Building ARC gave me an opportunity to design the reading experience I wanted. And now, it’s available on the Kindle iOS app!

Another favorite was training an LLM-RecSys Hybrid for Steerable Recommendations with Semantic IDs. I started this with the expectation that it would not work, and was shocked that the model could natively return recommendations based on natural language or item ID input. I still recall the “mind-blown” moment while watching it train—given an input Zelda game (typically only on Nintendo) and a request to filter for similar games on Xbox, it was able to recommend three open-world RPGs on Xbox.

I also shipped a few smaller prototypes, including building sub-agent capabilities into q-cli (before they were available anywhere) and a stock analysis app for my family.

✅ Health: I started running 5k weekly since July. While I had tried to do this previously, I was never consistent. Sticking to it led to noticeable improvements in my resting heart rate and VO2 max, as measured by my Apple Watch. Looking at the data from 2023 - 2025, I can see small but gradual improvements, which I hope to continue making progress on next year.

Resting heart rate from 2023 - 2025

V02 max from 2023 - 2025

❌ Snowboarding (do a black run in 2026): This goal fell short as I’ll have to skip the current season due to surgery. Nonetheless, my wife and I are happy with the progress we made earlier in the year (in Hakuba) and are eager to hit the slopes next season.

Health: Braces and jaw surgery

To fix my bite and prevent prematurely grinding down my molars, I started wearing braces in February and had jaw surgery in late November. I adapted to the braces more easily than expected, and am now in my third week of recovery from the surgery.

Career: Promoted to Principal and O1

I got promoted to Principal Applied Scientist. My O1-A visa was also approved around the same time. I’ve been enjoying the increased scope and learning that comes with the new role (though I’ve effectively been operating at this level for the past 12+ months; see point 26 here.)

Travel: Nagano and Las Vegas

My wife and I aim to travel at least once a year, ideally twice if possible. Our two trips this year were to Hakuba (a snow resort town, lesser-known than Niseko) and my first-ever trip to Las Vegas. The snowboarding and food in Hakuba were the best I’ve experienced, and I now have a new life goal to visit at least once a year, time and budget permitting. For Vegas, my top recommendations are Antelope Canyon, watching a show at The Sphere, and the Bellagio fountains (imagine the mechanical engineering involved in 1998!).

Statistics for 2025

Here are the top 20 most interacted-with pieces on my site.

Top 20 most interacted-with pieces in 2025

And here are the Google search metrics. While impressions increased from 1.97M to 3.39M (+71% YOY), clicks decreased from 56.5k to 42.2k (-25% YOY). Consequently, CTR dropped from 2.9% to 1.2% despite average position increasing from 24.6 to 17.7. I’m not exactly sure what’s driving this divergence. Perhaps Google’s AI Overviews or agentic traffic are inflating impressions without driving clicks.

Search traffic and trends in 2025

Goals for 2026

I’m keeping the same goals as 2025. I found myself stretching to meet the first two given my increased official scope at work, and I want the last two to solidify into lifelong habits.

• Write 6 substantive pieces
• Prototype 4 apps in public
• Health: Weekly 5k run + weights + healthy diet
• Snowboarding: Attempt a black run

If you found this useful, please cite this write-up as:

Yan, Ziyou. (Dec 2025). 2025 Year in Review. eugeneyan.com. https://eugeneyan.com/writing/2025-review/.

or

@article{yan20252025review,
  title   = {2025 Year in Review},
  author  = {Yan, Ziyou},
  journal = {eugeneyan.com},
  year    = {2025},
  month   = {Dec},
  url     = {https://eugeneyan.com/writing/2025-review/}
}