With stone foundation, Greek castles compete to be most up-to-date (9)

'most up-to-date' is the definition.
Both the answer and definition are superlative adjectives. Perhaps they are linked in a way I don't understand?

'with stone foundation greek castles compete' is the wordplay.
I cannot quite understand how this works, but
'stone' could be 'st' (abbreviation) and 'st' is present in the answer.
'greek' could be 'gr' (abbreviation for Greek) and 'gr' is found within the answer.
'compete' could be 'vie' (synonyms) and 'vie' is present in the answer.
The remaining letters 'oo' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'to be' is the link.

Can you help me to learn more?