Lief Tech — Dev, Business & Finance Blog
Lief Tech is a dev, business, and finance blog — practical writing on software engineering, AI tooling, solo-founder strategy, and personal finance, all from direct experience building and running a product.
What does Lief Tech cover?
Backend engineering with Spring Boot and Python, cloud infrastructure, AI-powered product development, stock market analysis, real estate, and personal finance. Posts are grounded in shipping real software and making real money decisions — not in theory.
Who writes Lief Tech?
A software engineer and founder with hands-on experience across backend systems, web platform standards, and solo product operations. New posts several times a week.
- 3D Gaussian Splatting vs Unreal Engine: Two Ways to Build a 3D World — and Where Each One Ships
- LLMs Inside Unreal Engine: The New Skills Game Developers Need in 2026
- Living With Claude Fable 5: How the Most Capable Model Changes the Way You Actually Work
- Luma's Bet: From Video Generator to a Single Model That Thinks in Pixels
- The Best AI Video Models in 2026: Types, Differences, and Where This Is All Going
- The Duolingo Founder Story: Luis von Ahn, a Green Owl, and the Plan to Make Education Free
- The Midjourney Founder Story: David Holz, the Company That Took No VC Money, and the $500M Bootstrap
- The Figma Founder Story: Drones, a Meme Generator, and the $20 Billion Deal That Got Blocked
- The Spotify Founder Story: How Daniel Ek Beat Free Music by Being Faster Than Theft
- The Stripe Founder Story: Two Brothers From Limerick and Seven Lines of Code
- Elon Musk's X Money Says It Will Pay You 6% on Savings. Is It Too Good to Be True?
- Commercial Real Estate Investing: The Complete Guide
- Samsung vs SK Hynix: the HBM battle that will decide Korea's AI chip future
- The end of jeonse and what it means for renters in Korea
- TSMC and the AI chip bottleneck Wall Street can't price correctly
- ISA: the Korean tax-free savings account most people don't use
- This Summer's Heat Wave: Key Points of the 2026 Vulnerable Population Protection Plan
- Majoring in AI or Software? Don't Miss the New AI Academic Incentive Student Loan
- Today's Financial Benefit: 2026 Small Business Stability Voucher (Up to 250,000 KRW)
226 posts
Weekly Retrospective — July Week 2, 2026
As it's gotten easier to build services with AI, I've been watching so many of them come to life and fade away.
Weekly Retrospective — July Week 1, 2026
It's been a while since I wrote my retrospective — I usually write one every week.
The Duolingo Founder Story: Luis von Ahn, a Green Owl, and the Plan to Make Education Free
Luis von Ahn invented CAPTCHA, sold reCAPTCHA to Google, and won a MacArthur 'genius' grant — then walked away from all of it to solve a problem from his childhood in Guatemala: education that only the rich can afford. How a computer scientist who was obsessed with harnessing human attention built Duolingo into a public company with hundreds of millions of learners.
3D Gaussian Splatting vs Unreal Engine: Two Ways to Build a 3D World — and Where Each One Ships
3D Gaussian Splatting captures reality; Unreal Engine authors it. This is a practical comparison of how you actually build a scene with each pipeline, what the result looks and behaves like, and the real productions — from Polycam captures to LED-wall virtual production — where each one ships.
LLMs Inside Unreal Engine: The New Skills Game Developers Need in 2026
In 2026, wiring a large language model into an Unreal Engine NPC stopped being a research demo and became a plugin you install from FAB. NVIDIA's ACE Game Agent SDK, Convai's NeuroSync, on-device small language models — here's what actually changed, and the concrete skills a game developer needs to build a character that talks back.
The Midjourney Founder Story: David Holz, the Company That Took No VC Money, and the $500M Bootstrap
David Holz spent nearly a decade building Leap Motion, raised $94M, and watched it sell for a fraction of its peak. Then he did the opposite: he started Midjourney with no outside capital, ~40 people, and a Discord bot — and turned it into a reported $500M-ARR business. How a burned VC skeptic built one of the most profitable companies in AI.
Living With Claude Fable 5: How the Most Capable Model Changes the Way You Actually Work
The Claude Fable 5 release notes tell you the parameters that changed. They don't tell you how it reshapes your day-to-day workflow — the timeouts, the prompts you have to unlearn, and why 'high' effort is usually the right default. A practitioner's field notes after a few weeks of building on Fable 5.
Luma's Bet: From Video Generator to a Single Model That Thinks in Pixels
Luma AI started as a 3D-capture app, became a top-tier AI video model with Ray3, and is now wagering its future on Uni-1 — a single 'unified intelligence' model that reasons in language and renders in pixels in one pass. Here's what Luma actually shipped, why the $4B valuation, and where it's heading.
The Figma Founder Story: Drones, a Meme Generator, and the $20 Billion Deal That Got Blocked
Dylan Field dropped out of college on a $100k Thiel grant, then spent four years building nothing anyone could see — burning through ideas like drones and a meme generator before landing on 'Google Docs for design.' How Figma survived a near-failure stealth period, a blocked $20B Adobe acquisition, and IPO'd in 2025 at $68 billion.
Weekly Retrospective — June Week 4, 2026
I spent a hectic month—three services, a review, a competition application, and more.
The Spotify Founder Story: How Daniel Ek Beat Free Music by Being Faster Than Theft
When Daniel Ek started Spotify, the music industry was being hollowed out by piracy and everyone agreed the answer was lawsuits. Ek disagreed. He bet that you could not sue people away from free music — you could only out-experience it. The story of how a working-class kid from a Stockholm suburb made streaming start in 200 milliseconds, survived years of brutal licensing fights, and turned 'better than stealing' into a $30-billion company.
The Best AI Video Models in 2026: Types, Differences, and Where This Is All Going
Veo 3.1, Kling 3.0, Runway Gen-4.5, Seedance, and the strange case of Sora's shutdown. A clear-eyed map of the AI video generation models that actually matter in 2026 — how they differ, which one to pick for what, and where the field is heading.
Claude Fable 5 and Mythos 5: What the New Models Change, and How They Perform
Anthropic's Claude Fable 5 is now its most capable widely released model, and Claude Mythos 5 brings the same engine to Project Glasswing. Here's what actually changed in the API, why thinking is now always on, and what the performance gains look like in practice.
The Stripe Founder Story: Two Brothers From Limerick and Seven Lines of Code
Stripe is now one of the most valuable private companies on earth, processing payments for millions of businesses. But it started with two teenage brothers from rural Ireland who had already sold one company before they could legally drink — and who were annoyed that taking money online was absurdly hard. Here's how Patrick and John Collison built it.
The Replit Founder Story: From a Browser Hack in Amman to a Billion-Dollar IDE
Replit lets anyone write and run code in a browser, and is now valued north of a billion dollars. But it started as an open-source side project by a kid in Amman, Jordan, who refused to believe that programming had to be hard to start. Here's how Amjad Masad turned a browser hack into a company betting on the next billion software creators.
Elon Musk's X Money Says It Will Pay You 6% on Savings. Is It Too Good to Be True?
X Money, the fintech app built inside X, is reportedly offering 6% APY on savings plus 3% cash back — roughly 15x the US national average savings rate. Here's how the offer works, where the 6% really comes from, and the catches worth understanding before you move your cash.
The Nvidia Founder Story: A Denny's Booth, a Sega Bailout, and 30 Days From Death
Nvidia is now one of the most valuable companies on earth and the engine room of the entire AI boom. But it began in a Denny's booth in 1993, nearly died after its first chip flopped, and survived only because the founder told a customer the truth and a Japanese games company paid him anyway. Here's how Jensen Huang built it.
Anthropic Shipped Its Most Powerful Claude Yet — Then the US Government Pulled the Plug
On June 9, 2026, Anthropic released Fable 5 and Mythos 5, its most capable models ever. Three days later it suspended access after a US export-control directive limited the models to US nationals. Here's what happened, why national security got involved, and what it means for the AI industry.
Weekly Retrospective — June Week 3, 2026
It feels like I've just been frantically tackling one thing after another, and somehow it's already the end of June.
When You Should NOT Use Sub-Agents
Sub-agents are the default reflex for any hard task now — but Anthropic's own engineering guidance is blunt about where they backfire. A look at the token math, the decomposition test, and the failure modes that mean a single agent is the right call.
The Notion Founder Story: Noodles, Kyoto, and a Rewrite That Saved the Company
Notion is a $10B+ workspace used by over 100 million people — but in 2015 it was two founders in a cheap Kyoto apartment who had scrapped their code, laid off their only employees, and were borrowing money from mom. Here's how Ivan Zhao and Simon Last almost died, then rebuilt.
From Agent Engineering to Harness Engineering to Loop Engineering
The discipline of building with LLMs has shifted three times in two years — from crafting agents, to crafting the harness around them, to crafting the loop the agent runs inside. Here's what each shift actually changed and why it matters.
Commercial Real Estate Investing: The Complete Guide
A practical, numbers-first walkthrough of investing in commercial retail property — how yield really works, the location and tenant signals that matter, the due diligence that protects your downside, and the taxes and exit math most first-time buyers get wrong.
How to Research Your App's Target Audience (With Real Examples)
A practical method for identifying and validating your app's real target audience — using App Store reviews, community listening, competitor changelogs, and micro-experiments, with examples from Notion, Calm, and Duolingo.
Why Developers Leave Claude for Open-Source Models
Cost, privacy, refusals, and a narrowing capability gap are pushing developers from Claude's API to self-hosted open-source models. Here's what that shift looks like from the inside.
From Side Project to Acquisition: The Moltbook Story
A first-person account of building Moltbook — a developer knowledge-capture tool — from a weekend prototype to a successful acquisition, and what the journey taught me about shipping with intent.
MCP, Skills, Hooks, Sub-agents: What They Are and How to Choose
Claude Code offers four extension layers — MCP, skills, hooks, and sub-agents — that look similar but operate at fundamentally different depths. Here's a clear framework for choosing the right one.
Back to Basics: LLM, RAG, and GraphRAG
A clear-eyed look at what large language models, retrieval-augmented generation, and graph-based RAG actually are — and when each one earns its place.
My personal CLI-replacement tool for running multiple MVPs solo—should I open-source it?
A CLI-replacement tool I built to run and manage multiple solo projects—shared standards, per-project issue tracking, and accumulated Git history/context, all in one place.
Kubernetes vs AWS Lambda: When Serverless Actually Saves You Money
A clear-eyed look at the real cost math behind Kubernetes and AWS Lambda — and how to know which one is bleeding your budget without you noticing.