Exercise 2: What Happens to an Auto Mode Network When Google Adds a New Region — Possible Solution
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An Auto mode VPC network automatically creates one new subnet, using
a predefined range inside 10.128.0.0/9, in every real region Google
Cloud adds - with no explicit action required from the team at all.
This means the moment Google launches a new region, the team's
network silently gains a new subnet in a region they never asked for
and have no plans to use.

This isn't dangerous by itself, but it is a real, automatic change to
the team's own network footprint that happens without their
involvement or approval, and it consumes part of the predefined
10.128.0.0/9 address space regardless of whether the team ever
deploys anything into that new subnet.

Custom mode avoids this entirely, because subnet creation is always a
deliberate, manual action - a Custom mode network never gains a new
subnet unless someone on the team explicitly creates one. This is
exactly why Google's own real documentation recommends Custom mode
for production: it keeps the network's own footprint fully under the
team's own control rather than expanding automatically as the
platform itself grows.

ANSWER: Their Auto mode network automatically and silently creates a
new subnet in the new region, using a predefined address range, with
no action or approval from the team. Custom mode would have avoided
this, since it never creates a subnet unless someone deliberately
does so - which is the real reason Google recommends Custom mode for
production networks.

WHY THIS WORKS AS AN ANSWER
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This correctly identifies the specific real automatic behavior Auto
mode networks have (an unrequested subnet appearing in every new
region) and ties it directly to Google's own stated real reasoning
for recommending Custom mode in production instead.