api_version suffix is unconditionally appended to custom base_url, breaking enterprise proxies

[yann-combarnous]

Environment

• google-genai version: 1.64.0
• Python: 3.13.2

Description

When a custom base_url is passed (e.g. via langchain-google-genai's ChatGoogleGenerativeAI),
the SDK internally sets _http_options.api_version = "v1beta" and appends it to the base URL
when constructing request paths.

This makes it impossible to use an enterprise reverse proxy (e.g. WSO2 API Gateway) that exposes
the Gemini API at a clean path without the /v1beta segment, because every request ends up routed
to a non-existent path on the proxy.

Reproduction

from google import genai

client = genai.Client(
    api_key="unused",
    http_options={"base_url": "https://my-proxy.example.com/gemini/"},
)

#Actual requests go to: https://my-proxy.example.com/gemini/v1beta/models/...
#Expected:              https://my-proxy.example.com/gemini/models/...

Current workaround

# Directly mutate internal state after construction — fragile against SDK updates
client._api_client._http_options.api_version = ""

Expected behavior

http_options should expose an api_version field (or equivalent) that is honoured when a
base_url is explicitly set, defaulting to "" when the caller opts into a fully-qualified base
URL. Alternatively, if base_url already contains the version segment the SDK should not append it
again.