Sync client ignores timeout for unreachable site (but async client works as expected)

[yazmolod]

Hi! I'm encountering an issue where the timeout argument seems to behave inconsistently between the synchronous and asynchronous clients.

I'm trying to query a site that delays responses based on geolocation or VPN - if you're from the "wrong" country, it just hangs (likely silently blocks the connection). I'm setting a timeout of 3 seconds to avoid this, but only the async client behaves as expected.

Code to reproduce

import asyncio
from time import perf_counter
import httpx

HOST = "https://nspd.gov.ru"
sync_client = httpx.Client(base_url=HOST, timeout=3)
async_client = httpx.AsyncClient(base_url=HOST, timeout=3)

if __name__ == "__main__":
    t0 = perf_counter()

    try:    
        asyncio.run(async_client.get("/api"))
    except httpx.ConnectTimeout:
        t1 = perf_counter()

    try:
        sync_client.get("/api")
    except httpx.ConnectTimeout:
        t2 = perf_counter()

    try:
        httpx.get(HOST + "/api", timeout=3)
    except httpx.ConnectTimeout:
        t3 = perf_counter()

    print(
        'Async client timeout: %.2f' % (t1 - t0),
        'Sync client timeout: %.2f' % (t2 - t1),
        'No client timeout: %.2f' % (t3 - t2),
        sep='\n'
    )

Output:

Async client timeout: 3.01  
Sync client timeout: 18.03  
No client timeout: 18.27  

Expected:

All three should timeout after ~3 seconds.

Actual:

Only the async client respects the timeout. Both sync and top-level httpx.get(...) calls hang for ~18 seconds.

Environment

httpx 0.28.1
python 3.13.0

Is this a bug or am I misunderstanding how timeout should work for sync requests? Would appreciate any insight - thanks in advance!