title_body: When smart contracts launch, will every node on the network have to run every contract transaction?
upvoted_answer: The validation of the state change of a smart contact in the eUTXO model is done when accepting the transaction. When a node validates a transaction, the node determines if the transaction is allowed to use a certain output as an input. The transaction will look up the script provided by the output's address and will execute the script if the transaction can use the output as an input. The node can validate multiple transactions in parallel if they are not consuming the same input.
  References:
  
  https://iohk.io/en/blog/posts/2021/04/13/plutus-what-you-need-to-know/
  https://iohk.io/en/blog/posts/2021/03/11/cardanos-extended-utxo-accounting-model/
  https://iohk.io/en/blog/posts/2021/03/12/cardanos-extended-utxo-accounting-model-part-2/