🛡️ Fixing ValueError: password cannot be longer than 72 bytes in Python 3.12 / 3.13 ( passlib + bcrypt )

When deploying FastAPI authentication routes using passlib[bcrypt] on Python 3.12 or Python 3.13 , newer versions of bcrypt ( >= 4.1.0 ) raise:

ValueError: password cannot be longer than 72 bytes, truncate manually if necessary

during passlib 's internal detect_wrap_bug startup check.

✅ The Instant Production Fix

Pin bcrypt==4.0.1 alongside passlib[bcrypt] in your requirements.txt :

fastapi uvicorn passlib[bcrypt] bcrypt==4.0.1 python-jose[cryptography] pydantic[email]

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