diff --git a/Configuration/PyReleaseValidation/python/relval_upgrade.py b/Configuration/PyReleaseValidation/python/relval_upgrade.py
index e6adaab29c36f..3949d4573dea4 100644
--- a/Configuration/PyReleaseValidation/python/relval_upgrade.py
+++ b/Configuration/PyReleaseValidation/python/relval_upgrade.py
@@ -58,8 +58,8 @@ def makeStepName(key,frag,step,suffix):
                                 stepList[specialType].append(stepMaker(key,frag[:-4],step.replace('RecoGlobal','HLT75e33'),specialWF.suffix))
                         # similar hacks for premixing
                         if 'PMX' in specialType:
-                            if 'GenSim' in step:
-                                s = step.replace('GenSim','Premix')+'PU' # later processing requires to have PU here
+                            if 'GenSim' in step or 'Gen' in step:
+                                s = step.replace('GenSim','Premix').replace('Gen','Premix')+'PU' # later processing requires to have PU here
                                 if step in specialWF.PU:
                                     stepMade = stepMaker(key,'PREMIX',s,specialWF.suffix)
                                     # append for combined
diff --git a/Configuration/PyReleaseValidation/python/upgradeWorkflowComponents.py b/Configuration/PyReleaseValidation/python/upgradeWorkflowComponents.py
index af10124b517b4..8b4139b59045d 100644
--- a/Configuration/PyReleaseValidation/python/upgradeWorkflowComponents.py
+++ b/Configuration/PyReleaseValidation/python/upgradeWorkflowComponents.py
@@ -2346,17 +2346,38 @@ def setupPU_(self, step, stepName, stepDict, k, properties):
         if "GenSim" in stepName:
             stepNamePmx = stepName.replace('GenSim','Premix')
             if not stepNamePmx in stepDict: stepDict[stepNamePmx] = {}
-            stepDict[stepNamePmx][k] = merge([
-                {
-                    '-s': 'GEN,SIM,DIGI:pdigi_valid',
-                    '--datatier': 'PREMIX',
-                    '--eventcontent': 'PREMIX',
-                    '--procModifiers': 'premix_stage1'
-                },
-                stepDict[stepName][k]
-            ])
-            if "ProdLike" in self.suffix:
-                stepDict[stepNamePmx][k] = merge([{'-s': 'GEN,SIM,DIGI'},stepDict[stepNamePmx][k]])
+            # avoid overwriting fastsim alternative
+            if not k in stepDict[stepNamePmx]:
+                stepDict[stepNamePmx][k] = merge([
+                    {
+                        '-s': 'GEN,SIM,DIGI:pdigi_valid',
+                        '--datatier': 'PREMIX',
+                        '--eventcontent': 'PREMIX',
+                        '--procModifiers': 'premix_stage1'
+                    },
+                    stepDict[stepName][k]
+                ])
+                if "ProdLike" in self.suffix:
+                    stepDict[stepNamePmx][k] = merge([{'-s': 'GEN,SIM,DIGI'},stepDict[stepNamePmx][k]])
+        # setup for stage 1 fastsim
+        elif "Gen" in stepName:
+            stepNamePmx = stepName.replace('Gen','Premix')
+            if not stepNamePmx in stepDict: stepDict[stepNamePmx] = {}
+            # avoid overwriting fullsim alternative
+            if not k in stepDict[stepNamePmx]:
+                stepDict[stepNamePmx][k] = merge([
+                    {
+                        '-s': 'GEN,SIM,RECOBEFMIX,DIGI:pdigi_valid',
+                        '--fast':'',
+                        '--datatier': 'PREMIX',
+                        '--eventcontent': 'PREMIX',
+                        '--procModifiers': 'premix_stage1'
+                    },
+                    stepDict[stepName][k]
+                ])
+                if "ProdLike" in self.suffix:
+                    # todo
+                    pass
         # setup for stage 2
         elif "Digi" in step or "Reco" in step:
             # go back to non-PU step version
@@ -2382,18 +2403,28 @@ def setupPU_(self, step, stepName, stepDict, k, properties):
                 else:
                     d["--procModifiers"] = "premix_stage2"
             stepDict[stepName][k] = d
-        # Increase the input file step number by one for Nano in combined stage1+stage2
-        elif "Nano"==step:
+        # setup for stage 2 fastsim
+        elif "FastSimRun3" in step:
             # go back to non-PU step version
             d = merge([stepDict[self.getStepName(step)][k]])
-            if "--filein" in d:
-                filein = d["--filein"]
-                m = re.search("step(?P<ind>\d+)_", filein)
-                if m:
-                    d["--filein"] = filein.replace(m.group(), "step%d_"%(int(m.group("ind"))+1))
+            if d is None: return
+            tmpsteps = []
+            for s in d["-s"].split(","):
+                if s == "DIGI" or "DIGI:" in s:
+                    tmpsteps.extend([s, "DATAMIX"])
+                else:
+                    tmpsteps.append(s)
+            d = merge([{"-s"             : ",".join(tmpsteps),
+                        "--datamix"      : "PreMix"},
+                       d])
+            if "--procModifiers" in d:
+                d["--procModifiers"] += ",premix_stage2"
+            else:
+                d["--procModifiers"] = "premix_stage2"
+            # for combined stage1+stage2
+            if "_PMXS1S2" in self.suffix:
+                d = merge([digiPremixLocalPileup, d])
             stepDict[stepName][k] = d
-            # run2/3 WFs use Nano (not NanoPU) in PU WF
-            stepDict[self.getStepName(step)][k] = merge([d])
     def condition(self, fragment, stepList, key, hasHarvest):
         if not 'PU' in key:
             return False
@@ -2412,6 +2443,7 @@ def workflow_(self, workflows, num, fragment, stepList, key):
     steps = [
     ],
     PU = [
+        'Gen',
         'GenSim',
         'GenSimHLBeamSpot',
         'GenSimHLBeamSpot14',
@@ -2432,6 +2464,7 @@ def workflow_(self, workflows, num, fragment, stepList, key):
         'RecoNano',
         'RecoNanoFakeHLT',
         'Nano',
+        'FastSimRun3',
     ],
     suffix = '_PMXS2',
     offset = 0.98,
@@ -2440,6 +2473,7 @@ def workflow_(self, workflows, num, fragment, stepList, key):
 upgradeWFs['PMXS1S2'] = UpgradeWorkflowPremix(
     steps = [],
     PU = [
+        'Gen',
         'GenSim',
         'GenSimHLBeamSpot',
         'GenSimHLBeamSpot14',
@@ -2452,6 +2486,7 @@ def workflow_(self, workflows, num, fragment, stepList, key):
         'RecoNano',
         'RecoNanoFakeHLT',
         'Nano',
+        'FastSimRun3',
     ],
     suffix = '_PMXS1S2',
     offset = 0.99,