I was experimenting with concurrent request handling on few platforms.
The aim of the experiment was to have a broad measure of the capacity bounds of s
Extending on Alexander's answer.
The GAE scaling logic is based on incoming traffic trend analysis.
The key for being able to handle your case - sudden spikes in traffic (which can't be takes into account in the trend analysis due to its variation speed) - is to have sufficient resident (idle) instances configured for your application to handle such traffic until GAE spins up additional dynamic instances. It can handle as high peaks as you want (if your pockets are deep enough).
See Scaling dynamic instances for more details.