I have Aranet4 CO2 monitors inside my apartment, one near my desk and one in the living room both at eye level and visible to me at all times when I’m in those spaces. Anecdotally, I find myself thinking “slower” @ 900+ ppm, and can even notice slightly worse thinking at levels as low as 750ppm.
I find indoor levels @ <600ppm to be ideal, but not always possible depending on if you have guests, air quality conditions of the day, etc.
I unfortunately only live in a space with 1 window, so ventilation can be difficult. However a single well placed fan facing outwards blowing towards the window improves indoor circulation. With the HVAC system fan also running, I can decrease indoor ppm by 50-100 in just 10-15 minutes.
If you don’t already periodically vent your space (or if you live in a nice enough climate, keep windows open all day), then I highly recommend you start doing so.
re: 1b (development likely impossible to kept secret given scale required)
I’m remind of Dylan Patel’s comments (semianalysis) on a recent episode of the Dwarkesh Podcast which goes something like:
Given the success we’ve seen in training SOTA models with constrained GPU resources (Deepseek), I don’t think it’s far fetched to think you can hide bleeding edge development. It turns out all you need is a few hundred of the smartest people in your country and a few thousand GPUs.
Hrm...sounds like the size of the Manhattan Project.