A Performance Evaluation of Flask (WSGI) and Fastapi (ASGI) Under High-Concurrency Workloads

Python web development is experiencing a paradigm shift from the traditional Synchronous Web Server Gateway Interface (WSGI) to the modern Asynchronous Server Gateway Interface (ASGI). While WSGI frameworks like Flask have existed for a long time as the industry standard for microservices, their blocking architecture inherently restricts performance under high-concurrency workloads. This research fills this specific gap completely by introducing a rigorous quantitative benchmark comparing Flask WSGI with FastAPI (ASGI). Through the construction of two functionally identical applications and rigorous controlled I/O-bound load testing using Apache JMeter, throughput, latency, and error rates are measured. Results show a stark contrast in stability; ASGI kept 100% reliability, WSGI failed by 76% under identical load. These findings have actionable implications for software developers that moving to asynchronous frameworks is not just an adaptation but a requirement in our current and high-throughput API environment.