Blog
Engineering notes from 9io.
How we build products, AI systems and trading infrastructure — and what we learn on the way. Written by the people who do the work, with the sources linked.
Algo trading
The look-ahead bias our backtester prevents, and the leaks it misses
Our daily backtester shows its detectors only past bars and fills stops pessimistically. What still leaks in, and a checklist for building your own.
5 October 2026 · 15 min read LLMsIs Claude nerfed? How to measure model drift yourself
Is Claude nerfed, or did something else change? Documented degradations, the changes that only look like one, and a nightly drift check with error bars.
3 October 2026 · 17 min read TestingHow we pinned down four intermittent bugs in React 19 and Python
Four bugs in a React 19 and Python stack that failed only some of the time, the condition behind each, and how we made each one show up on demand.
30 September 2026 · 10 min read