The unspectacular part that makes the difference
Maintenance is rarely noticed while it works. It gets noticed when it has been missing: a site that no longer starts after a PHP update, a hole that stood open for months, a backup that could not be restored.
So we treat maintenance as a task of its own with a fixed rhythm, not as something that runs along on the side.
Security in TYPO3
TYPO3 has a security team of its own that publishes vulnerabilities in the core and in extensions in a coordinated way. That is an advantage, because you find out reliably what is affected. It is also an obligation: publication also tells everyone else what to look for.
With every advisory we check whether the affected component exists in your installation, whether it is reachable from outside, and which version is running. Only then does it become clear how urgent it really is.
What we do not promise
We deliberately quote no fixed response times and no availability figures here. Numbers like that are only worth anything when they fit the actual environment, and we do not know yours before we have talked.
What we do instead: put the scope of the arrangement in writing before it starts. It then says what is covered, what happens at what interval, and what would be charged separately in a given case.