What is the recommended web server architecture for free-threaded Python 3.13+?

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With PEP 703 (free-threaded Python), threads can now run truly in parallel without the GIL. This changes the calculus for web frameworks:

  1. WSGI + ThreadPool: Pure sync, minimal overhead, direct parallelism
  2. ASGI + async: Event loop has overhead when dispatching to threads via run_in_executor()

In my benchmarks, a pure sync ThreadPoolExecutor approach is 3-4x faster for CPU-bound handlers than ASGI + threadpool, due to async boundary overhead.

Questions:

  • Should new frameworks for free-threaded Python be sync-first (WSGI)?
  • Is there work on optimizing ASGI for thread-based handlers?
  • Is a new standard needed that’s thread-native?
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