After trump agreement, a new suit shows 1st round control (ace or void) and slam interest. This applies at all levels with some exceptions.1

Bid at the cheapest level so a Control Bid in a suit would deny 1st round control in a lower ranked suit (that could have been bid but wasn’t).

1Notes and Exceptions for Discussion

  • Trial Bids are not played. So 1♠-2♠-3♦ under this agreement would be a Control Bid showing a very strong, unbalanced hand (but not worth 2♣) with ♦ control, but not club control. However this is of limited usefulness as a non 2♣ opening bid against parnter’s simple raise doesn not seem destined for slam - perhaps there is a better use for this bid… e.g. diamond shortage, game invitational)
  • Inverted Minors. 1♣-2♣-2♦/2♥/2♠. See Response to Inverted Minors.