diff --git a/Configuration/ProcessModifiers/python/run3_ecalclustering_cff.py b/Configuration/ProcessModifiers/python/run3_ecalclustering_cff.py
new file mode 100644
index 0000000000000..170677a51d9c4
--- /dev/null
+++ b/Configuration/ProcessModifiers/python/run3_ecalclustering_cff.py
@@ -0,0 +1,6 @@
+import FWCore.ParameterSet.Config as cms
+
+# This modifier is for ECAL Run3 clustering studies
+
+run3_ecalclustering =  cms.Modifier()
+
diff --git a/SimDataFormats/CaloAnalysis/interface/SimCluster.h b/SimDataFormats/CaloAnalysis/interface/SimCluster.h
index 09433efb7a06d..30b75545cc0dd 100644
--- a/SimDataFormats/CaloAnalysis/interface/SimCluster.h
+++ b/SimDataFormats/CaloAnalysis/interface/SimCluster.h
@@ -177,6 +177,9 @@ class SimCluster {
     fractions_.emplace_back(fraction);
   }
 
+  /** @brief add rechit energy */
+  void addHitEnergy(float energy) { energies_.emplace_back(energy); }
+
   /** @brief Returns list of rechit IDs and fractions for this SimCluster */
   std::vector<std::pair<uint32_t, float>> hits_and_fractions() const {
     std::vector<std::pair<uint32_t, float>> result;
@@ -186,12 +189,26 @@ class SimCluster {
     return result;
   }
 
+  /** @brief Returns list of rechit IDs and energies for this SimCluster */
+  std::vector<std::pair<uint32_t, float>> hits_and_energies() const {
+    assert(hits_.size() == energies_.size());
+    std::vector<std::pair<uint32_t, float>> result;
+    result.reserve(hits_.size());
+    for (size_t i = 0; i < hits_.size(); ++i) {
+      result.emplace_back(hits_[i], energies_[i]);
+    }
+    return result;
+  }
+
   /** @brief clear the hits and fractions list */
   void clearHitsAndFractions() {
     std::vector<uint32_t>().swap(hits_);
     std::vector<float>().swap(fractions_);
   }
 
+  /** @brief clear the energies list */
+  void clearHitsEnergy() { std::vector<float>().swap(energies_); }
+
   /** @brief returns the accumulated sim energy in the cluster */
   float simEnergy() const { return simhit_energy_; }
 
@@ -206,6 +223,7 @@ class SimCluster {
   float simhit_energy_;
   std::vector<uint32_t> hits_;
   std::vector<float> fractions_;
+  std::vector<float> energies_;
 
   math::XYZTLorentzVectorF theMomentum_;
 
diff --git a/SimDataFormats/CaloAnalysis/src/classes_def.xml b/SimDataFormats/CaloAnalysis/src/classes_def.xml
index 3d54f8b2be929..89a2b4c9f5aaf 100644
--- a/SimDataFormats/CaloAnalysis/src/classes_def.xml
+++ b/SimDataFormats/CaloAnalysis/src/classes_def.xml
@@ -8,8 +8,9 @@
   <class name="CaloParticleRefVector"/>
   <class name="CaloParticleRefProd"/>
   <class name="CaloParticleContainer"/>
-  <class name="SimCluster"  ClassVersion="3">
-   <version ClassVersion="3" checksum="1773780587"/>
+  <class name="SimCluster"  ClassVersion="4">
+    <version ClassVersion="4" checksum="3868743425"/>
+    <version ClassVersion="3" checksum="1773780587"/>
   </class>
   <class name="SimClusterCollection"/>
   <class name="edm::Wrapper<SimClusterCollection>"/>
diff --git a/SimGeneral/CaloAnalysis/plugins/CaloTruthAccumulator.cc b/SimGeneral/CaloAnalysis/plugins/CaloTruthAccumulator.cc
index 4dbc4252beef3..ff7e8a22fd75b 100644
--- a/SimGeneral/CaloAnalysis/plugins/CaloTruthAccumulator.cc
+++ b/SimGeneral/CaloAnalysis/plugins/CaloTruthAccumulator.cc
@@ -486,6 +486,7 @@ void CaloTruthAccumulator::finalizeEvent(edm::Event &event, edm::EventSetup cons
     for (auto &sc : *(output_.pSimClusters)) {
       auto hitsAndEnergies = sc.hits_and_fractions();
       sc.clearHitsAndFractions();
+      sc.clearHitsEnergy();
       for (auto &hAndE : hitsAndEnergies) {
         const float totalenergy = m_detIdToTotalSimEnergy[hAndE.first];
         float fraction = 0.;
@@ -495,6 +496,7 @@ void CaloTruthAccumulator::finalizeEvent(edm::Event &event, edm::EventSetup cons
           edm::LogWarning(messageCategory_)
               << "TotalSimEnergy for hit " << hAndE.first << " is 0! The fraction for this hit cannot be computed.";
         sc.addRecHitAndFraction(hAndE.first, fraction);
+        sc.addHitEnergy(hAndE.second);
       }
     }
   }
diff --git a/SimGeneral/MixingModule/python/caloTruthProducer_cfi.py b/SimGeneral/MixingModule/python/caloTruthProducer_cfi.py
index 071fa1cd7dc0f..a4bad8726d169 100644
--- a/SimGeneral/MixingModule/python/caloTruthProducer_cfi.py
+++ b/SimGeneral/MixingModule/python/caloTruthProducer_cfi.py
@@ -46,6 +46,18 @@
     simHitCollections = dict(hgc = caloParticles.simHitCollections.hgc + [cms.InputTag('g4SimHits','HFNoseHits')])
 )
 
+from Configuration.ProcessModifiers.run3_ecalclustering_cff import run3_ecalclustering
+run3_ecalclustering.toModify(
+        caloParticles,
+	simHitCollections = cms.PSet(
+            ecal = cms.VInputTag(
+                cms.InputTag('g4SimHits','EcalHitsEE'),
+                cms.InputTag('g4SimHits','EcalHitsEB'),
+                cms.InputTag('g4SimHits','EcalHitsES')
+            )
+	)
+)
+
 from Configuration.Eras.Modifier_fastSim_cff import fastSim
 fastSim.toReplaceWith(caloParticles, cms.PSet()) # don't allow this to run in fastsim
 
diff --git a/SimGeneral/MixingModule/python/digitizers_cfi.py b/SimGeneral/MixingModule/python/digitizers_cfi.py
index 12682181c7264..247acfe7a0415 100644
--- a/SimGeneral/MixingModule/python/digitizers_cfi.py
+++ b/SimGeneral/MixingModule/python/digitizers_cfi.py
@@ -102,7 +102,8 @@
 theDigitizersValid = cms.PSet(theDigitizers)
 theDigitizers.mergedtruth.select.signalOnlyTP = True
 
-phase2_hgcal.toModify( theDigitizersValid,
+from Configuration.ProcessModifiers.run3_ecalclustering_cff import run3_ecalclustering
+(run3_ecalclustering | phase2_hgcal).toModify( theDigitizersValid,
                        calotruth = cms.PSet( caloParticles ) ) # Doesn't HGCal need these also without validation?
 (premix_stage2 & phase2_hgcal).toModify(theDigitizersValid, calotruth = dict(premixStage1 = True))