Hey neighbor,

This week had a number that stopped me cold. One billion. That's how many people are now using ChatGPT every month. Let's put that in perspective — and then get to the other big stories.

THIS WEEK IN AI

ChatGPT just crossed 1 billion active users

ChatGPT crossed 1 billion active users this month — making it one of the fastest-growing consumer products in human history. To put that in perspective: it took Facebook over eight years to reach 1 billion users. ChatGPT did it in less than three.

One in eight people on earth now uses ChatGPT every month. That's not a tech trend anymore. That's a global shift in how people work, learn, and get information.

What this means for you: if you haven't tried ChatGPT yet, you're now in a shrinking minority. And if you have tried it, the tool you're using is one of the most widely adopted pieces of software in human history. Understanding how to use it well is becoming as important as knowing how to use email.

An AI just solved 10 math problems that had stumped humanity for decades

OpenAI's Astra model solved 10 previously unsolved math problems with verified proofs — a genuine scientific first, not a benchmark stunt.

Here's why this matters in plain English. These weren't easy problems — they were problems that the world's best mathematicians had been working on for years or decades without solutions. An AI sat down, worked through them, and produced verified correct proofs.

This is different from AI being good at writing emails or summarizing documents. This is AI doing something that required genuine creative reasoning — the kind of thinking that was supposed to be uniquely human. It's a significant moment in the history of science.

Google Gemini just hit 1 billion monthly users too

Google's Gemini hit 1 billion monthly users — reaching the milestone at almost exactly the same time as ChatGPT's announcement.

Two competing AI assistants both hitting 1 billion users in the same week tells you something important: this isn't a winner-take-all market. People are using multiple AI tools for different purposes — just like they use Google for search but YouTube for video and Gmail for email. The AI ecosystem is maturing into something more like the broader internet than a single dominant platform.

What this means for you: the competition between ChatGPT and Gemini is good for users. It keeps both tools improving fast and keeps prices low.

PLAIN ENGLISH EXPLAINER

What does it mean that AI "solved" math problems — and why should non-mathematicians care?

When we say AI solved unsolved math problems, we mean something very specific. These are problems where mathematicians knew what the question was but couldn't find a proof — a logical argument that definitively shows why the answer is correct.

Think of it like a very hard crossword puzzle where you know all the clues but can't figure out some of the answers. OpenAI's Astra didn't just guess — it worked through the logic step by step and produced complete, verified solutions that human mathematicians confirmed were correct.

Why should you care if you're not a mathematician? Because math is the foundation of everything in science and engineering. Breakthroughs in mathematics often lead to breakthroughs in medicine, physics, computer science, and more — sometimes decades later. The proofs solved this week might lead to advances we can't predict yet.

More immediately: frontier AI leaders are increasingly arguing that AI has entered the early stages of an intelligence explosion — where AI systems begin accelerating their own development. An AI that can solve problems humans couldn't solve is a meaningful step in that direction. This is worth paying attention to.

TOOL OF THE WEEK

Try this: GPT-5.6 Luna — the most powerful ChatGPT just got 80% cheaper

GPT-5.6 Luna prices dropped 80% this week — making one of the most capable AI models available significantly more affordable for everyday users and small businesses.

If you've been using the free version of ChatGPT and wondering whether it's worth paying for the Plus subscription, this week's price drop makes it a much easier decision.

Here are three things worth trying with a more powerful model:

→ Give it a genuinely complex task — planning a major life decision, analyzing a financial situation, researching a big purchase — and see how it handles nuance compared to the free version

→ Ask it to help you understand something you've been confused about for a long time — a medical condition, a legal concept, a financial term

→ Ask it to write something creative — a speech, a poem, a story — and see how the quality compares to what you've experienced before

The free version is still excellent. But if you've been curious about the paid tier, prices just got significantly more reasonable.

NEIGHBOR'S THOUGHT

One billion neighbors

One billion people using ChatGPT. One billion using Gemini. The same week.

I started this newsletter because I believed that understanding AI was going to matter — not just for tech workers but for everyone. For parents. For people changing careers. For retirees trying to make sense of a world that's changing faster than they expected.

Nineteen weeks in, I feel more certain of that than when we started. One billion people using these tools means AI literacy is no longer optional. It's becoming as essential as reading, as fundamental as knowing how to use a phone.

That's not scary. That's an opportunity. And you're ahead of most people just by understanding what's happening.

One billion neighbors using AI. And you're one of them — with the advantage of actually understanding what you're using and why.

That matters. See you next week.

UNTIL NEXT WEEK

That's your week in AI — Issue #19. Nearly five months in and the milestones keep arriving.

If this newsletter has helped you feel more informed and less overwhelmed by AI, share it with one person this week. Every new reader is a neighbor who gets to understand what's happening.

See you next Thursday. ☀️

— The AI Neighbor Team
theaineighbor.com