Being nitpicky about Python specifically, Python not necessarily single-threaded; gunicorn gets you a multiprocess HTTP/WSGI server if you configure it to. asyncio and gevent have made it easier to do things actually-concurrently. Judicious use of generator functions lets you stream results back instead of blocking I/O for big chunks. And we have threads. Yeah, the Global Interpreter Lock is still hanging around, it's not the fastest language, but there are ways to produce a Docker image of an API written in Python which can handle thousands of concurrent HTTP requests and actively use all available CPU cores to do intensive computation.

Here I thought you would bring multiprocessing and process pool in Python.