Is a 57-degree CPU temperature normal for a new MacBook Air during coding?

Apple does not document their expected operating temperature ranges and thermal limits, and AFAIK Apple does not provide a documented and supported API means for accessing the thermal sensor data and thermal profiles.

Pragmatically, Apple silicon processors — and most every other modern processor — will run correctly, will actively cool and/or actively throttle as temperatures increase, or will shut down (hard) when core temperatures approach hardware-damaging ranges.

Per reports, 14 (completely saturated) M4 cores runs the performance cores at around 90 to 100°C, and the efficiency cores around 85 to 90°C, and this with the active cooling busy.

Related: Is my Macbook at normal Temperatures? - Apple Community

57C is nothing to worry about.

While I don't work with Xcode, I am doing coding for an embedded processor with an RTOS and multiple peripheral interfaces on my M4 MacBook Air (24GB RAM, 512GB SSD). When doing a full, clean build of the project (currently mostly C language) I see temps get to 75-85C with pretty much all cores spinning up sometimes peaking a bit higher. That is at a room ambient of 20-24C. They do drop quite quickly after the build is done.

I can sometimes see similar spikes when processing RAW photos with my image processing app.

FWIW, at similar ambient temps, doing what I am currently doing root now (web surfing and typing this response), my CPU temps sit at around 36-40C. It's a few degrees higher than my M1 MacBook Air.

There is really not much to worry about as long as those temps are present for hours at a time.

Seems a little on the cool side. Code harder.

Keep your Mac laptop within acceptable operating temperatures - Apple Support