diff --git a/packages/react-reconciler/src/ReactFiberLane.new.js b/packages/react-reconciler/src/ReactFiberLane.new.js
index 878fc433f3c53..c5aef527a422a 100644
--- a/packages/react-reconciler/src/ReactFiberLane.new.js
+++ b/packages/react-reconciler/src/ReactFiberLane.new.js
@@ -11,6 +11,25 @@ import type {FiberRoot} from './ReactInternalTypes';
 
 // TODO: Ideally these types would be opaque but that doesn't work well with
 // our reconciler fork infra, since these leak into non-reconciler packages.
+export type LanePriority =
+  | 0
+  | 1
+  | 2
+  | 3
+  | 4
+  | 5
+  | 6
+  | 7
+  | 8
+  | 9
+  | 10
+  | 11
+  | 12
+  | 13
+  | 14
+  | 15
+  | 16
+  | 17;
 
 export type Lanes = number;
 export type Lane = number;
@@ -24,6 +43,28 @@ import {
 } from 'shared/ReactFeatureFlags';
 import {isDevToolsPresent} from './ReactFiberDevToolsHook.new';
 
+export const SyncLanePriority: LanePriority = 12;
+
+const InputContinuousHydrationLanePriority: LanePriority = 11;
+export const InputContinuousLanePriority: LanePriority = 10;
+
+const DefaultHydrationLanePriority: LanePriority = 9;
+export const DefaultLanePriority: LanePriority = 8;
+
+const TransitionHydrationPriority: LanePriority = 7;
+export const TransitionPriority: LanePriority = 6;
+
+const RetryLanePriority: LanePriority = 5;
+
+const SelectiveHydrationLanePriority: LanePriority = 4;
+
+const IdleHydrationLanePriority: LanePriority = 3;
+export const IdleLanePriority: LanePriority = 2;
+
+const OffscreenLanePriority: LanePriority = 1;
+
+export const NoLanePriority: LanePriority = 0;
+
 // Lane values below should be kept in sync with getLabelsForLanes(), used by react-devtools-scheduling-profiler.
 // If those values are changed that package should be rebuilt and redeployed.
 
@@ -127,19 +168,29 @@ export const NoTimestamp = -1;
 let nextTransitionLane: Lane = TransitionLane1;
 let nextRetryLane: Lane = RetryLane1;
 
+// "Registers" used to "return" multiple values
+// Used by getHighestPriorityLanes and getNextLanes:
+let return_highestLanePriority: LanePriority = DefaultLanePriority;
+
 function getHighestPriorityLanes(lanes: Lanes | Lane): Lanes {
   switch (getHighestPriorityLane(lanes)) {
     case SyncLane:
+      return_highestLanePriority = SyncLanePriority;
       return SyncLane;
     case InputContinuousHydrationLane:
+      return_highestLanePriority = InputContinuousHydrationLanePriority;
       return InputContinuousHydrationLane;
     case InputContinuousLane:
+      return_highestLanePriority = InputContinuousLanePriority;
       return InputContinuousLane;
     case DefaultHydrationLane:
+      return_highestLanePriority = DefaultHydrationLanePriority;
       return DefaultHydrationLane;
     case DefaultLane:
+      return_highestLanePriority = DefaultLanePriority;
       return DefaultLane;
     case TransitionHydrationLane:
+      return_highestLanePriority = TransitionHydrationPriority;
       return TransitionHydrationLane;
     case TransitionLane1:
     case TransitionLane2:
@@ -157,20 +208,26 @@ function getHighestPriorityLanes(lanes: Lanes | Lane): Lanes {
     case TransitionLane14:
     case TransitionLane15:
     case TransitionLane16:
+      return_highestLanePriority = TransitionPriority;
       return lanes & TransitionLanes;
     case RetryLane1:
     case RetryLane2:
     case RetryLane3:
     case RetryLane4:
     case RetryLane5:
+      return_highestLanePriority = RetryLanePriority;
       return lanes & RetryLanes;
     case SelectiveHydrationLane:
+      return_highestLanePriority = SelectiveHydrationLanePriority;
       return SelectiveHydrationLane;
     case IdleHydrationLane:
+      return_highestLanePriority = IdleHydrationLanePriority;
       return IdleHydrationLane;
     case IdleLane:
+      return_highestLanePriority = IdleLanePriority;
       return IdleLane;
     case OffscreenLane:
+      return_highestLanePriority = OffscreenLanePriority;
       return OffscreenLane;
     default:
       if (__DEV__) {
@@ -179,6 +236,7 @@ function getHighestPriorityLanes(lanes: Lanes | Lane): Lanes {
         );
       }
       // This shouldn't be reachable, but as a fallback, return the entire bitmask.
+      return_highestLanePriority = DefaultLanePriority;
       return lanes;
   }
 }
@@ -187,10 +245,12 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
   // Early bailout if there's no pending work left.
   const pendingLanes = root.pendingLanes;
   if (pendingLanes === NoLanes) {
+    return_highestLanePriority = NoLanePriority;
     return NoLanes;
   }
 
   let nextLanes = NoLanes;
+  let nextLanePriority = NoLanePriority;
 
   const suspendedLanes = root.suspendedLanes;
   const pingedLanes = root.pingedLanes;
@@ -202,10 +262,12 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
     const nonIdleUnblockedLanes = nonIdlePendingLanes & ~suspendedLanes;
     if (nonIdleUnblockedLanes !== NoLanes) {
       nextLanes = getHighestPriorityLanes(nonIdleUnblockedLanes);
+      nextLanePriority = return_highestLanePriority;
     } else {
       const nonIdlePingedLanes = nonIdlePendingLanes & pingedLanes;
       if (nonIdlePingedLanes !== NoLanes) {
         nextLanes = getHighestPriorityLanes(nonIdlePingedLanes);
+        nextLanePriority = return_highestLanePriority;
       }
     }
   } else {
@@ -213,9 +275,11 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
     const unblockedLanes = pendingLanes & ~suspendedLanes;
     if (unblockedLanes !== NoLanes) {
       nextLanes = getHighestPriorityLanes(unblockedLanes);
+      nextLanePriority = return_highestLanePriority;
     } else {
       if (pingedLanes !== NoLanes) {
         nextLanes = getHighestPriorityLanes(pingedLanes);
+        nextLanePriority = return_highestLanePriority;
       }
     }
   }
@@ -249,6 +313,8 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
     ) {
       // Keep working on the existing in-progress tree. Do not interrupt.
       return wipLanes;
+    } else {
+      return_highestLanePriority = nextLanePriority;
     }
   }
 
@@ -443,6 +509,9 @@ export function getLanesToRetrySynchronouslyOnError(root: FiberRoot): Lanes {
   return NoLanes;
 }
 
+export function returnNextLanesPriority() {
+  return return_highestLanePriority;
+}
 export function includesNonIdleWork(lanes: Lanes) {
   return (lanes & NonIdleLanes) !== NoLanes;
 }
@@ -548,6 +617,13 @@ export function higherPriorityLane(a: Lane, b: Lane) {
   return a !== NoLane && a < b ? a : b;
 }
 
+export function higherLanePriority(
+  a: LanePriority,
+  b: LanePriority,
+): LanePriority {
+  return a !== NoLanePriority && a > b ? a : b;
+}
+
 export function createLaneMap<T>(initial: T): LaneMap<T> {
   // Intentionally pushing one by one.
   // https://v8.dev/blog/elements-kinds#avoid-creating-holes
diff --git a/packages/react-reconciler/src/ReactFiberLane.old.js b/packages/react-reconciler/src/ReactFiberLane.old.js
index d4010468f0d74..926a3da32cbab 100644
--- a/packages/react-reconciler/src/ReactFiberLane.old.js
+++ b/packages/react-reconciler/src/ReactFiberLane.old.js
@@ -11,6 +11,25 @@ import type {FiberRoot} from './ReactInternalTypes';
 
 // TODO: Ideally these types would be opaque but that doesn't work well with
 // our reconciler fork infra, since these leak into non-reconciler packages.
+export type LanePriority =
+  | 0
+  | 1
+  | 2
+  | 3
+  | 4
+  | 5
+  | 6
+  | 7
+  | 8
+  | 9
+  | 10
+  | 11
+  | 12
+  | 13
+  | 14
+  | 15
+  | 16
+  | 17;
 
 export type Lanes = number;
 export type Lane = number;
@@ -24,6 +43,28 @@ import {
 } from 'shared/ReactFeatureFlags';
 import {isDevToolsPresent} from './ReactFiberDevToolsHook.old';
 
+export const SyncLanePriority: LanePriority = 12;
+
+const InputContinuousHydrationLanePriority: LanePriority = 11;
+export const InputContinuousLanePriority: LanePriority = 10;
+
+const DefaultHydrationLanePriority: LanePriority = 9;
+export const DefaultLanePriority: LanePriority = 8;
+
+const TransitionHydrationPriority: LanePriority = 7;
+export const TransitionPriority: LanePriority = 6;
+
+const RetryLanePriority: LanePriority = 5;
+
+const SelectiveHydrationLanePriority: LanePriority = 4;
+
+const IdleHydrationLanePriority: LanePriority = 3;
+export const IdleLanePriority: LanePriority = 2;
+
+const OffscreenLanePriority: LanePriority = 1;
+
+export const NoLanePriority: LanePriority = 0;
+
 // Lane values below should be kept in sync with getLabelsForLanes(), used by react-devtools-scheduling-profiler.
 // If those values are changed that package should be rebuilt and redeployed.
 
@@ -127,19 +168,29 @@ export const NoTimestamp = -1;
 let nextTransitionLane: Lane = TransitionLane1;
 let nextRetryLane: Lane = RetryLane1;
 
+// "Registers" used to "return" multiple values
+// Used by getHighestPriorityLanes and getNextLanes:
+let return_highestLanePriority: LanePriority = DefaultLanePriority;
+
 function getHighestPriorityLanes(lanes: Lanes | Lane): Lanes {
   switch (getHighestPriorityLane(lanes)) {
     case SyncLane:
+      return_highestLanePriority = SyncLanePriority;
       return SyncLane;
     case InputContinuousHydrationLane:
+      return_highestLanePriority = InputContinuousHydrationLanePriority;
       return InputContinuousHydrationLane;
     case InputContinuousLane:
+      return_highestLanePriority = InputContinuousLanePriority;
       return InputContinuousLane;
     case DefaultHydrationLane:
+      return_highestLanePriority = DefaultHydrationLanePriority;
       return DefaultHydrationLane;
     case DefaultLane:
+      return_highestLanePriority = DefaultLanePriority;
       return DefaultLane;
     case TransitionHydrationLane:
+      return_highestLanePriority = TransitionHydrationPriority;
       return TransitionHydrationLane;
     case TransitionLane1:
     case TransitionLane2:
@@ -157,20 +208,26 @@ function getHighestPriorityLanes(lanes: Lanes | Lane): Lanes {
     case TransitionLane14:
     case TransitionLane15:
     case TransitionLane16:
+      return_highestLanePriority = TransitionPriority;
       return lanes & TransitionLanes;
     case RetryLane1:
     case RetryLane2:
     case RetryLane3:
     case RetryLane4:
     case RetryLane5:
+      return_highestLanePriority = RetryLanePriority;
       return lanes & RetryLanes;
     case SelectiveHydrationLane:
+      return_highestLanePriority = SelectiveHydrationLanePriority;
       return SelectiveHydrationLane;
     case IdleHydrationLane:
+      return_highestLanePriority = IdleHydrationLanePriority;
       return IdleHydrationLane;
     case IdleLane:
+      return_highestLanePriority = IdleLanePriority;
       return IdleLane;
     case OffscreenLane:
+      return_highestLanePriority = OffscreenLanePriority;
       return OffscreenLane;
     default:
       if (__DEV__) {
@@ -179,6 +236,7 @@ function getHighestPriorityLanes(lanes: Lanes | Lane): Lanes {
         );
       }
       // This shouldn't be reachable, but as a fallback, return the entire bitmask.
+      return_highestLanePriority = DefaultLanePriority;
       return lanes;
   }
 }
@@ -187,10 +245,12 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
   // Early bailout if there's no pending work left.
   const pendingLanes = root.pendingLanes;
   if (pendingLanes === NoLanes) {
+    return_highestLanePriority = NoLanePriority;
     return NoLanes;
   }
 
   let nextLanes = NoLanes;
+  let nextLanePriority = NoLanePriority;
 
   const suspendedLanes = root.suspendedLanes;
   const pingedLanes = root.pingedLanes;
@@ -202,10 +262,12 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
     const nonIdleUnblockedLanes = nonIdlePendingLanes & ~suspendedLanes;
     if (nonIdleUnblockedLanes !== NoLanes) {
       nextLanes = getHighestPriorityLanes(nonIdleUnblockedLanes);
+      nextLanePriority = return_highestLanePriority;
     } else {
       const nonIdlePingedLanes = nonIdlePendingLanes & pingedLanes;
       if (nonIdlePingedLanes !== NoLanes) {
         nextLanes = getHighestPriorityLanes(nonIdlePingedLanes);
+        nextLanePriority = return_highestLanePriority;
       }
     }
   } else {
@@ -213,9 +275,11 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
     const unblockedLanes = pendingLanes & ~suspendedLanes;
     if (unblockedLanes !== NoLanes) {
       nextLanes = getHighestPriorityLanes(unblockedLanes);
+      nextLanePriority = return_highestLanePriority;
     } else {
       if (pingedLanes !== NoLanes) {
         nextLanes = getHighestPriorityLanes(pingedLanes);
+        nextLanePriority = return_highestLanePriority;
       }
     }
   }
@@ -249,6 +313,8 @@ export function getNextLanes(root: FiberRoot, wipLanes: Lanes): Lanes {
     ) {
       // Keep working on the existing in-progress tree. Do not interrupt.
       return wipLanes;
+    } else {
+      return_highestLanePriority = nextLanePriority;
     }
   }
 
@@ -443,6 +509,9 @@ export function getLanesToRetrySynchronouslyOnError(root: FiberRoot): Lanes {
   return NoLanes;
 }
 
+export function returnNextLanesPriority() {
+  return return_highestLanePriority;
+}
 export function includesNonIdleWork(lanes: Lanes) {
   return (lanes & NonIdleLanes) !== NoLanes;
 }
@@ -548,6 +617,13 @@ export function higherPriorityLane(a: Lane, b: Lane) {
   return a !== NoLane && a < b ? a : b;
 }
 
+export function higherLanePriority(
+  a: LanePriority,
+  b: LanePriority,
+): LanePriority {
+  return a !== NoLanePriority && a > b ? a : b;
+}
+
 export function createLaneMap<T>(initial: T): LaneMap<T> {
   // Intentionally pushing one by one.
   // https://v8.dev/blog/elements-kinds#avoid-creating-holes