Thanks to carguy75 for recommending this low viscosity brake fluid upgrade, Bosch ESI6 gives quicker brake pedal response in stop and go city traffic at sub-zero temperatures, every winter area car should be running low viscosity brake fluid.
https://www.boschautoparts.com/p/esi-brake-fluid

No problem. I am glad you have good results with the ES16 brake fluid.

I use that brake fluid in all my cars and have not been disappointed yet.

WOW When I first read this post I thought it was a joke. So I went to the Bosch ES16 site and read their claims. Nowhere does it say anything about a "quicker pedal response". It is all about life expectancy and boiling points. So, please explain the physics behind your claim that you get quicker pedal response with this fluid. Brake fluid is nothing more than a non compressible fluid between the master cylinder and the calipers. If brake fluid is replaced occasionally it all works the same. As long as there is little to no water in the fluid. I await your response.

That's excellent advice.
I used Textar DOT4 LV low-viscosity brake fluid, but it has simpler characteristics compared to Bosch brake fluid. Textar needs to be changed every 2 years, while Bosch needs to be changed every 3 years. Also, Bosch has a higher wet boiling point. Accordingly, it has a higher safety margin against overheating and a longer service life.

Low-viscosity brake fluid remains liquid in freezing temperatures and ensures an immediate response from ABS and ESP systems, while regular brake fluid is thicker and flows more slowly through the micro-valves of the ABS unit in cold weather. In hot weather, there is not much difference during normal driving, but for example, at high temperatures during racing, it is better to use low-viscosity fluid.

I bought into Bosch ESI6 brake fluid for the 3 year flush period claim not looking at the much lower viscosity and surprised how well this LV fluid makes brake pedal feel at -20∘F we've had last few nights in this area. AI Overview says; Low temperatures, particularly below −40∘F / -40∘C cause DOT 3 brake fluid to significantly increase in viscosity, making it thicker and slower to flow. This thickening results in a sluggish, "spongy" brake pedal feel, sluggish brake response, and potentially, ABS system errors. Didn't ask mechanic to check water content of brake fluid before we flushed a few days ago but last fall was around 2%.

The Lexus owners manual says 3 year replacement also. This is for DOT3. So, how is this better? The number of people on this forum that operate their vehicles at or below -40C or F (same thing) is probably below 1% and that is being generous.

I wouldn't trust the manufacturer's recommendations.

Bought 10 quarts of this recently good product (and good value) but I can't tell any difference in the brake pedal.

With calm driving, without constant extreme braking and not in freezing temperatures, there will most likely be no difference. Especially if the old brake fluid was good (low water content).

Normal driving, hasn't been super cold yet (might not happen again this year). Now I want it to get bitter cold so I can test.

The ES16 lasts twice as long as DOT 3 brake fluid so it would be a 6 year service life in the RX350 application if pushed. However, I would still go no longer than 3 years in my RX350 before flushing. I used to flush DOT3 every 2 years.

The ES16 is a good quality brake fluid that allows the ABS system to work smoother and quicker due to it high boiling point and lower viscosity as well as having a longer service life, however many RX350 owners will probably never push their RX350 to its braking limits to tell the difference over the DOT 3 unless in extreme conditions like freezing temperatures, emergency braking requiring ABS or a lot of down hill braking.

Note: The RX350 AWD system requires the brakes to work quickly as well to control wheel spin and maintain traction so having a lower viscosity brake fluid benefits that function as well.