Mistral() silently accepts api_key=None with no env var fallback — error only at call time

[YousefZahran1]

Bug

Mistral() with no api_key and no MISTRAL_API_KEY env var constructs successfully with api_key=None. No env var lookup happens at init time. Misconfiguration is only discovered when the first API call fails — the opposite of how OpenAI and Anthropic SDKs behave.

Reproduce (mistralai 2.4.5, no API key needed)

import os, inspect
from mistralai.client import Mistral

os.environ.pop('MISTRAL_API_KEY', None)

client = Mistral()                          # No exception raised
print('Client created with no key')        # This prints

sig = inspect.signature(Mistral.__init__)
print(sig.parameters['api_key'].default)   # None — no env var fallback

Expected

Check MISTRAL_API_KEY at construction time. Raise ValueError immediately if no key found — matching OpenAI and Anthropic SDK behavior.

Suggested Fix

def __init__(self, api_key=None, ...):
    if api_key is None:
        api_key = os.environ.get('MISTRAL_API_KEY')
    if api_key is None:
        raise ValueError(
            'No API key provided. Pass api_key=... or set MISTRAL_API_KEY env var.'
        )

Happy to open a PR.

— Youssef Ibrahim | github.com/YousefZahran1