diff --git a/README.md b/README.md
index 351860f1..b3cdb0bb 100644
--- a/README.md
+++ b/README.md
@@ -347,6 +347,11 @@ export interface AutoroutingPhaseProps extends RoutingTolerances {
    * direction unconstrained.
    */
   busFanoutDirections?: Record<BusName, BusFanoutDirection>;
+  /**
+   * Padding between the union of the fanout source pads and the shared
+   * boundary where fanout traces terminate.
+   */
+  fanoutBoundaryPadding?: FanoutBoundaryPadding;
 }
 ```
 
@@ -422,6 +427,12 @@ export interface BreakoutProps extends Omit<
   paddingRight?: Distance;
   paddingTop?: Distance;
   paddingBottom?: Distance;
+  /**
+   * Padding between the union of the fanout source pads and the shared
+   * boundary where fanout traces terminate. This is independent of the
+   * breakout group's layout padding.
+   */
+  fanoutBoundaryPadding?: FanoutBoundaryPadding;
 }
 ```