diff --git a/ortools/sat/BUILD b/ortools/sat/BUILD
index 8d749bbcf7..3e21a7a135 100644
--- a/ortools/sat/BUILD
+++ b/ortools/sat/BUILD
@@ -86,11 +86,9 @@ cc_library(
     visibility = ["//visibility:public"],
     deps = [
         ":cp_model_cc_proto",
-        ":cp_model_loader",
         ":cp_model_search",
         ":cp_model_utils",
         ":integer",
-        ":integer_search",
         ":model",
         ":sat_base",
         "//ortools/base",
diff --git a/ortools/sat/cp_model_solver.cc b/ortools/sat/cp_model_solver.cc
index 899a5822c7..38526f5a68 100644
--- a/ortools/sat/cp_model_solver.cc
+++ b/ortools/sat/cp_model_solver.cc
@@ -1092,6 +1092,230 @@ std::function<SatParameters(Model*)> NewSatParameters(
 
 namespace {
 
+// Registers a callback that will export variables bounds fixed at level 0 of
+// the search. This should not be registered to a LNS search.
+void RegisterVariableBoundsLevelZeroExport(
+    const CpModelProto& model_proto, SharedBoundsManager* shared_bounds_manager,
+    Model* model) {
+  CHECK(shared_bounds_manager != nullptr);
+  int saved_trail_index = 0;
+  const auto broadcast_level_zero_bounds =
+      [&model_proto, saved_trail_index, model, shared_bounds_manager](
+          const std::vector<IntegerVariable>& modified_vars) mutable {
+        CpModelMapping* const mapping = model->GetOrCreate<CpModelMapping>();
+
+        std::vector<int> model_variables;
+        std::vector<int64> new_lower_bounds;
+        std::vector<int64> new_upper_bounds;
+        absl::flat_hash_set<int> visited_variables;
+
+        // Inspect the modified IntegerVariables.
+        auto* integer_trail = model->Get<IntegerTrail>();
+        for (const IntegerVariable& var : modified_vars) {
+          const IntegerVariable positive_var = PositiveVariable(var);
+          const int model_var =
+              mapping->GetProtoVariableFromIntegerVariable(positive_var);
+          if (model_var == -1 || visited_variables.contains(model_var)) {
+            // TODO(user): I don't think we should see the same model_var twice
+            // here so maybe we don't need the visited_variables.contains()
+            // part.
+            continue;
+          }
+
+          visited_variables.insert(model_var);
+          const int64 new_lb =
+              integer_trail->LevelZeroLowerBound(positive_var).value();
+          const int64 new_ub =
+              integer_trail->LevelZeroUpperBound(positive_var).value();
+          // TODO(user): We could imagine an API based on atomic<int64>
+          // that could preemptively check if this new bounds are improving.
+          model_variables.push_back(model_var);
+          new_lower_bounds.push_back(new_lb);
+          new_upper_bounds.push_back(new_ub);
+        }
+
+        // Inspect the newly modified Booleans.
+        auto* trail = model->Get<Trail>();
+        for (; saved_trail_index < trail->Index(); ++saved_trail_index) {
+          const Literal fixed_literal = (*trail)[saved_trail_index];
+          const int model_var = mapping->GetProtoVariableFromBooleanVariable(
+              fixed_literal.Variable());
+          if (model_var == -1 || visited_variables.contains(model_var)) {
+            // If the variable is already visited, it should mean that this
+            // Boolean also has an IntegerVariable view, and we should already
+            // have set its bound correctly.
+            continue;
+          }
+
+          visited_variables.insert(model_var);
+          model_variables.push_back(model_var);
+          if (fixed_literal.IsPositive()) {
+            new_lower_bounds.push_back(1);
+            new_upper_bounds.push_back(1);
+          } else {
+            new_lower_bounds.push_back(0);
+            new_upper_bounds.push_back(0);
+          }
+        }
+
+        if (!model_variables.empty()) {
+          const WorkerInfo* const worker_info =
+              model->GetOrCreate<WorkerInfo>();
+          shared_bounds_manager->ReportPotentialNewBounds(
+              model_proto, worker_info->worker_id, worker_info->worker_name,
+              model_variables, new_lower_bounds, new_upper_bounds);
+        }
+      };
+
+  model->GetOrCreate<GenericLiteralWatcher>()
+      ->RegisterLevelZeroModifiedVariablesCallback(broadcast_level_zero_bounds);
+}
+
+// Registers a callback to import new variables bounds stored in the
+// shared_bounds_manager. These bounds are imported at level 0 of the search
+// in the linear scan minimize function.
+void RegisterVariableBoundsLevelZeroImport(
+    const CpModelProto& model_proto, SharedBoundsManager* shared_bounds_manager,
+    Model* model) {
+  CHECK(shared_bounds_manager != nullptr);
+  auto* integer_trail = model->GetOrCreate<IntegerTrail>();
+  const WorkerInfo* const worker_info = model->GetOrCreate<WorkerInfo>();
+  CpModelMapping* const mapping = model->GetOrCreate<CpModelMapping>();
+
+  const auto& import_level_zero_bounds = [&model_proto, shared_bounds_manager,
+                                          model, integer_trail, worker_info,
+                                          mapping]() {
+    std::vector<int> model_variables;
+    std::vector<int64> new_lower_bounds;
+    std::vector<int64> new_upper_bounds;
+    shared_bounds_manager->GetChangedBounds(worker_info->worker_id,
+                                            &model_variables, &new_lower_bounds,
+                                            &new_upper_bounds);
+    bool new_bounds_have_been_imported = false;
+    for (int i = 0; i < model_variables.size(); ++i) {
+      const int model_var = model_variables[i];
+      // This can happen if a boolean variables is forced to have an
+      // integer view in one thread, and not in another thread.
+      if (!mapping->IsInteger(model_var)) continue;
+      const IntegerVariable var = mapping->Integer(model_var);
+      const IntegerValue new_lb(new_lower_bounds[i]);
+      const IntegerValue new_ub(new_upper_bounds[i]);
+      const IntegerValue old_lb = integer_trail->LowerBound(var);
+      const IntegerValue old_ub = integer_trail->UpperBound(var);
+      const bool changed_lb = new_lb > old_lb;
+      const bool changed_ub = new_ub < old_ub;
+      if (!changed_lb && !changed_ub) continue;
+
+      new_bounds_have_been_imported = true;
+      if (VLOG_IS_ON(3)) {
+        const IntegerVariableProto& var_proto =
+            model_proto.variables(model_var);
+        const std::string& var_name =
+            var_proto.name().empty()
+                ? absl::StrCat("anonymous_var(", model_var, ")")
+                : var_proto.name();
+        LOG(INFO) << "  '" << worker_info->worker_name
+                  << "' imports new bounds for " << var_name << ": from ["
+                  << old_lb << ", " << old_ub << "] to [" << new_lb << ", "
+                  << new_ub << "]";
+      }
+
+      if (changed_lb &&
+          !integer_trail->Enqueue(IntegerLiteral::GreaterOrEqual(var, new_lb),
+                                  {}, {})) {
+        return false;
+      }
+      if (changed_ub &&
+          !integer_trail->Enqueue(IntegerLiteral::LowerOrEqual(var, new_ub), {},
+                                  {})) {
+        return false;
+      }
+    }
+    if (new_bounds_have_been_imported &&
+        !model->GetOrCreate<SatSolver>()->FinishPropagation()) {
+      return false;
+    }
+    return true;
+  };
+  model->GetOrCreate<LevelZeroCallbackHelper>()->callbacks.push_back(
+      import_level_zero_bounds);
+}
+
+// Registers a callback that will report improving objective best bound.
+// It will be called each time new objective bound are propagated at level zero.
+void RegisterObjectiveBestBoundExport(
+    IntegerVariable objective_var,
+    SharedResponseManager* shared_response_manager, Model* model) {
+  std::string worker_name = model->GetOrCreate<WorkerInfo>()->worker_name;
+  auto* integer_trail = model->Get<IntegerTrail>();
+  const auto broadcast_objective_lower_bound =
+      [worker_name, objective_var, integer_trail,
+       shared_response_manager](const std::vector<IntegerVariable>& unused) {
+        shared_response_manager->UpdateInnerObjectiveBounds(
+            worker_name, integer_trail->LevelZeroLowerBound(objective_var),
+            integer_trail->LevelZeroUpperBound(objective_var));
+      };
+  model->GetOrCreate<GenericLiteralWatcher>()
+      ->RegisterLevelZeroModifiedVariablesCallback(
+          broadcast_objective_lower_bound);
+}
+
+// Registers a callback to import new objective bounds. It will be called each
+// time the search main loop is back to level zero. Note that it the presence of
+// assumptions, this will not happend until the set of assumptions is changed.
+void RegisterObjectiveBoundsImport(
+    SharedResponseManager* shared_response_manager, Model* model) {
+  auto* solver = model->GetOrCreate<SatSolver>();
+  auto* integer_trail = model->GetOrCreate<IntegerTrail>();
+  auto* worker_info = model->GetOrCreate<WorkerInfo>();
+  auto* objective = model->GetOrCreate<ObjectiveDefinition>();
+  const auto import_objective_bounds = [solver, integer_trail, worker_info,
+                                        objective, shared_response_manager]() {
+    if (solver->AssumptionLevel() != 0) return true;
+    bool propagate = false;
+
+    const IntegerValue external_lb =
+        shared_response_manager->GetInnerObjectiveLowerBound();
+    const IntegerValue current_lb =
+        integer_trail->LowerBound(objective->objective_var);
+    if (external_lb > current_lb) {
+      if (!integer_trail->Enqueue(IntegerLiteral::GreaterOrEqual(
+                                      objective->objective_var, external_lb),
+                                  {}, {})) {
+        return false;
+      }
+      propagate = true;
+    }
+
+    const IntegerValue external_ub =
+        shared_response_manager->GetInnerObjectiveUpperBound();
+    const IntegerValue current_ub =
+        integer_trail->UpperBound(objective->objective_var);
+    if (external_ub < current_ub) {
+      if (!integer_trail->Enqueue(IntegerLiteral::LowerOrEqual(
+                                      objective->objective_var, external_ub),
+                                  {}, {})) {
+        return false;
+      }
+      propagate = true;
+    }
+
+    if (!propagate) return true;
+
+    VLOG(2) << "'" << worker_info->worker_name
+            << "' imports objective bounds: external ["
+            << objective->ScaleIntegerObjective(external_lb) << ", "
+            << objective->ScaleIntegerObjective(external_ub) << "], current ["
+            << objective->ScaleIntegerObjective(current_lb) << ", "
+            << objective->ScaleIntegerObjective(current_ub) << "]";
+
+    return solver->FinishPropagation();
+  };
+
+  model->GetOrCreate<LevelZeroCallbackHelper>()->callbacks.push_back(
+      import_objective_bounds);
+}
+
 // Loads a CpModelProto inside the given model.
 // This should only be called once on a given 'Model' class.
 //
@@ -1301,6 +1525,26 @@ void LoadCpModel(const CpModelProto& model_proto,
       RegisterObjectiveBoundsImport(shared_response_manager, model);
     }
   }
+
+  // Cache the relavant data for RINS variables.
+  if (model->Get<SharedRINSNeighborhoodManager>() != nullptr) {
+    auto* integer_trail = model->GetOrCreate<IntegerTrail>();
+    auto* lp_dispatcher = model->GetOrCreate<LinearProgrammingDispatcher>();
+    auto* rins_vars = model->GetOrCreate<RINSVariables>();
+    IntegerVariable size = integer_trail->NumIntegerVariables();
+    for (IntegerVariable positive_var(0); positive_var < size;
+         positive_var += 2) {
+      RINSVariable rins_var;
+      rins_var.positive_var = positive_var;
+      rins_var.model_var =
+          mapping->GetProtoVariableFromIntegerVariable(positive_var);
+      rins_var.lp = gtl::FindWithDefault(*lp_dispatcher, positive_var, nullptr);
+
+      if (rins_var.lp != nullptr && rins_var.model_var >= 0) {
+        rins_vars->vars.push_back(rins_var);
+      }
+    }
+  }
 }
 
 // Solves an already loaded cp_model_proto.
@@ -1335,26 +1579,6 @@ void SolveLoadedCpModel(const CpModelProto& model_proto,
         model_proto, mapping->GetVariableMapping(), fixed_search, model);
   }
 
-  if (model->Get<SharedRINSNeighborhoodManager>() != nullptr) {
-    // Cache the relavant data for RINS variables.
-    auto* integer_trail = model->GetOrCreate<IntegerTrail>();
-    auto* lp_dispatcher = model->GetOrCreate<LinearProgrammingDispatcher>();
-    auto* rins_vars = model->GetOrCreate<RINSVariables>();
-    IntegerVariable size = integer_trail->NumIntegerVariables();
-    for (IntegerVariable positive_var(0); positive_var < size;
-         positive_var += 2) {
-      RINSVariable rins_var;
-      rins_var.positive_var = positive_var;
-      rins_var.model_var =
-          mapping->GetProtoVariableFromIntegerVariable(positive_var);
-      rins_var.lp = gtl::FindWithDefault(*lp_dispatcher, positive_var, nullptr);
-
-      if (rins_var.lp != nullptr && rins_var.model_var >= 0) {
-        rins_vars->vars.push_back(rins_var);
-      }
-    }
-  }
-
   const auto solution_observer = [&model_proto, &model, &solution_info,
                                   &shared_response_manager]() {
     CpSolverResponse response;
@@ -1401,54 +1625,32 @@ void SolveLoadedCpModel(const CpModelProto& model_proto,
     const SatSolver::Status status = ResetAndSolveIntegerProblem({}, model);
 
     if (status == SatSolver::Status::FEASIBLE) {
-      bool hint_is_valid = true;
-      if (model_proto.has_objective() && parameters.optimize_with_core()) {
-        // We need to fix the lower bound of the objective variable.
-        // If linearization_level = 0, the objective_var is not linked with
-        // the model. We recompute its value from scratch.
-        int64 objective_value = 0;
-        for (int i = 0; i < model_proto.objective().vars_size(); ++i) {
-          objective_value += model_proto.objective().coeffs(i) *
-                             model->Get(LowerBound(mapping->Integer(
-                                 model_proto.objective().vars(i))));
+      const int old_size = solution_info.size();
+      solution_info += "[hint]";
+      solution_observer();
+      solution_info.resize(old_size);
+
+      if (!model_proto.has_objective()) {
+        if (parameters.enumerate_all_solutions()) {
+          model->Add(
+              ExcludeCurrentSolutionWithoutIgnoredVariableAndBacktrack());
+        } else {
+          return;
         }
+      } else {
+        // Restrict the objective. Note that since we call the solution observer
+        // above, the shared_response_manager objective should be up to date.
+        model->GetOrCreate<SatSolver>()->Backtrack(0);
         IntegerTrail* integer_trail = model->GetOrCreate<IntegerTrail>();
         if (!integer_trail->Enqueue(
-                IntegerLiteral::GreaterOrEqual(objective_var,
-                                               IntegerValue(objective_value)),
+                IntegerLiteral::LowerOrEqual(
+                    objective_var,
+                    shared_response_manager->GetInnerObjectiveUpperBound()),
                 {}, {})) {
-          hint_is_valid = false;
-          model->GetOrCreate<SatSolver>()->Backtrack(0);
-        }
-      }
-      if (hint_is_valid) {
-        const int old_size = solution_info.size();
-        solution_info += "[hint]";
-        solution_observer();
-        solution_info.resize(old_size);
-
-        if (!model_proto.has_objective()) {
-          if (parameters.enumerate_all_solutions()) {
-            model->Add(
-                ExcludeCurrentSolutionWithoutIgnoredVariableAndBacktrack());
-          } else {
-            return;
-          }
-        } else {
-          IntegerTrail* integer_trail = model->GetOrCreate<IntegerTrail>();
-          IntegerValue current_internal_objective =
-              integer_trail->LowerBound(objective_var);
-          // Restrict the objective.
-          model->GetOrCreate<SatSolver>()->Backtrack(0);
-          if (!integer_trail->Enqueue(
-                  IntegerLiteral::LowerOrEqual(objective_var,
-                                               current_internal_objective - 1),
-                  {}, {})) {
-            shared_response_manager->NotifyThatImprovingProblemIsInfeasible(
-                absl::StrCat(solution_info, "[hint]"));
-            shared_response_manager->SetStatsFromModel(model);
-            return;
-          }
+          shared_response_manager->NotifyThatImprovingProblemIsInfeasible(
+              absl::StrCat(solution_info, "[hint]"));
+          shared_response_manager->SetStatsFromModel(model);
+          return;
         }
       }
     }
@@ -1473,10 +1675,6 @@ void SolveLoadedCpModel(const CpModelProto& model_proto,
     }
   } else {
     // Optimization problem.
-    const CpObjectiveProto& obj = model_proto.objective();
-    VLOG(2) << obj.vars_size() << " terms in the proto objective.";
-    VLOG(2) << "Initial num_bool: " << model->Get<SatSolver>()->NumVariables();
-
     if (parameters.optimize_with_core()) {
       std::vector<IntegerVariable> linear_vars;
       std::vector<IntegerValue> linear_coeffs;
@@ -2417,6 +2615,8 @@ CpSolverResponse SolveCpModel(const CpModelProto& model_proto, Model* model) {
     if (log_search) {
       LOG(INFO) << absl::StrFormat("*** starting sequential search at %.2fs",
                                    wall_timer.Get());
+      LOG(INFO) << "Initial num_bool: "
+                << model->Get<SatSolver>()->NumVariables();
     }
     SolveLoadedCpModel(new_cp_model_proto, &shared_response_manager, model);
   }
diff --git a/ortools/sat/integer_search.cc b/ortools/sat/integer_search.cc
index 8c3021936e..1b51acc970 100644
--- a/ortools/sat/integer_search.cc
+++ b/ortools/sat/integer_search.cc
@@ -759,22 +759,5 @@ SatSolver::Status SolveIntegerProblemWithLazyEncoding(Model* model) {
   return ResetAndSolveIntegerProblem(/*assumptions=*/{}, model);
 }
 
-void LogNewSolution(const std::string& event_or_solution_count,
-                    double time_in_seconds, double obj_best, double obj_lb,
-                    double obj_ub, const std::string& solution_info) {
-  const std::string obj_next =
-      absl::StrFormat("next:[%.9g,%.9g]", obj_lb, obj_ub);
-  LOG(INFO) << absl::StrFormat("#%-5s %6.2fs best:%-5.9g %-15s %s",
-                               event_or_solution_count, time_in_seconds,
-                               obj_best, obj_next, solution_info);
-}
-
-void LogNewSatSolution(const std::string& event_or_solution_count,
-                       double time_in_seconds,
-                       const std::string& solution_info) {
-  LOG(INFO) << absl::StrFormat("#%-5s %6.2fs  %s", event_or_solution_count,
-                               time_in_seconds, solution_info);
-}
-
 }  // namespace sat
 }  // namespace operations_research
diff --git a/ortools/sat/integer_search.h b/ortools/sat/integer_search.h
index 6160894c85..574af47d98 100644
--- a/ortools/sat/integer_search.h
+++ b/ortools/sat/integer_search.h
@@ -206,16 +206,6 @@ std::vector<std::function<LiteralIndex()>> CompleteHeuristics(
     const std::vector<std::function<LiteralIndex()>>& incomplete_heuristics,
     const std::function<LiteralIndex()>& completion_heuristic);
 
-// Prints out a new optimization solution in a fixed format.
-void LogNewSolution(const std::string& event_or_solution_count,
-                    double time_in_seconds, double obj_best, double obj_lb,
-                    double obj_ub, const std::string& solution_info);
-
-// Prints out a new satisfiability solution in a fixed format.
-void LogNewSatSolution(const std::string& event_or_solution_count,
-                       double time_in_seconds,
-                       const std::string& solution_info);
-
 }  // namespace sat
 }  // namespace operations_research
 
diff --git a/ortools/sat/lns.h b/ortools/sat/lns.h
index 96d2a5e4bf..67b7b9754b 100644
--- a/ortools/sat/lns.h
+++ b/ortools/sat/lns.h
@@ -20,7 +20,7 @@
 #include <vector>
 
 #if !defined(__PORTABLE_PLATFORM__)
- #include "ortools/base/threadpool.h"
+#include "ortools/base/threadpool.h"
 #endif  // __PORTABLE_PLATFORM__
 
 namespace operations_research {
diff --git a/ortools/sat/synchronization.cc b/ortools/sat/synchronization.cc
index 32704e778c..f9c6e1067b 100644
--- a/ortools/sat/synchronization.cc
+++ b/ortools/sat/synchronization.cc
@@ -16,11 +16,9 @@
 #include "absl/container/flat_hash_set.h"
 #include "ortools/base/stl_util.h"
 #include "ortools/sat/cp_model.pb.h"
-#include "ortools/sat/cp_model_loader.h"
 #include "ortools/sat/cp_model_search.h"
 #include "ortools/sat/cp_model_utils.h"
 #include "ortools/sat/integer.h"
-#include "ortools/sat/integer_search.h"
 #include "ortools/sat/model.h"
 #include "ortools/sat/sat_base.h"
 
@@ -77,6 +75,27 @@ SharedResponseManager::SharedResponseManager(bool log_updates,
       wall_timer_(*wall_timer),
       solutions_(/*num_solutions_to_keep=*/10) {}
 
+namespace {
+
+void LogNewSolution(const std::string& event_or_solution_count,
+                    double time_in_seconds, double obj_best, double obj_lb,
+                    double obj_ub, const std::string& solution_info) {
+  const std::string obj_next =
+      absl::StrFormat("next:[%.9g,%.9g]", obj_lb, obj_ub);
+  LOG(INFO) << absl::StrFormat("#%-5s %6.2fs best:%-5.9g %-15s %s",
+                               event_or_solution_count, time_in_seconds,
+                               obj_best, obj_next, solution_info);
+}
+
+void LogNewSatSolution(const std::string& event_or_solution_count,
+                       double time_in_seconds,
+                       const std::string& solution_info) {
+  LOG(INFO) << absl::StrFormat("#%-5s %6.2fs  %s", event_or_solution_count,
+                               time_in_seconds, solution_info);
+}
+
+}  // namespace
+
 void SharedResponseManager::UpdateInnerObjectiveBounds(
     const std::string& worker_info, IntegerValue lb, IntegerValue ub) {
   absl::MutexLock mutex_lock(&mutex_);
@@ -272,7 +291,7 @@ void SharedResponseManager::NewSolution(const CpSolverResponse& response,
     std::string solution_info = response.solution_info();
     if (model != nullptr) {
       absl::StrAppend(&solution_info,
-                      " num_bool:", model->Get<SatSolver>()->NumVariables());
+                      " num_bool:", model->Get<Trail>()->NumVariables());
     }
 
     if (model_proto_.has_objective()) {
@@ -407,219 +426,5 @@ void SharedBoundsManager::GetChangedBounds(
   }
 }
 
-void RegisterVariableBoundsLevelZeroExport(
-    const CpModelProto& model_proto, SharedBoundsManager* shared_bounds_manager,
-    Model* model) {
-  CHECK(shared_bounds_manager != nullptr);
-  int saved_trail_index = 0;
-  const auto broadcast_level_zero_bounds =
-      [&model_proto, saved_trail_index, model, shared_bounds_manager](
-          const std::vector<IntegerVariable>& modified_vars) mutable {
-        CpModelMapping* const mapping = model->GetOrCreate<CpModelMapping>();
-
-        std::vector<int> model_variables;
-        std::vector<int64> new_lower_bounds;
-        std::vector<int64> new_upper_bounds;
-        absl::flat_hash_set<int> visited_variables;
-
-        // Inspect the modified IntegerVariables.
-        auto* integer_trail = model->Get<IntegerTrail>();
-        for (const IntegerVariable& var : modified_vars) {
-          const IntegerVariable positive_var = PositiveVariable(var);
-          const int model_var =
-              mapping->GetProtoVariableFromIntegerVariable(positive_var);
-          if (model_var == -1 || visited_variables.contains(model_var)) {
-            // TODO(user): I don't think we should see the same model_var twice
-            // here so maybe we don't need the visited_variables.contains()
-            // part.
-            continue;
-          }
-
-          visited_variables.insert(model_var);
-          const int64 new_lb =
-              integer_trail->LevelZeroLowerBound(positive_var).value();
-          const int64 new_ub =
-              integer_trail->LevelZeroUpperBound(positive_var).value();
-          // TODO(user): We could imagine an API based on atomic<int64>
-          // that could preemptively check if this new bounds are improving.
-          model_variables.push_back(model_var);
-          new_lower_bounds.push_back(new_lb);
-          new_upper_bounds.push_back(new_ub);
-        }
-
-        // Inspect the newly modified Booleans.
-        auto* trail = model->Get<Trail>();
-        for (; saved_trail_index < trail->Index(); ++saved_trail_index) {
-          const Literal fixed_literal = (*trail)[saved_trail_index];
-          const int model_var = mapping->GetProtoVariableFromBooleanVariable(
-              fixed_literal.Variable());
-          if (model_var == -1 || visited_variables.contains(model_var)) {
-            // If the variable is already visited, it should mean that this
-            // Boolean also has an IntegerVariable view, and we should already
-            // have set its bound correctly.
-            continue;
-          }
-
-          visited_variables.insert(model_var);
-          model_variables.push_back(model_var);
-          if (fixed_literal.IsPositive()) {
-            new_lower_bounds.push_back(1);
-            new_upper_bounds.push_back(1);
-          } else {
-            new_lower_bounds.push_back(0);
-            new_upper_bounds.push_back(0);
-          }
-        }
-
-        if (!model_variables.empty()) {
-          const WorkerInfo* const worker_info =
-              model->GetOrCreate<WorkerInfo>();
-          shared_bounds_manager->ReportPotentialNewBounds(
-              model_proto, worker_info->worker_id, worker_info->worker_name,
-              model_variables, new_lower_bounds, new_upper_bounds);
-        }
-      };
-
-  model->GetOrCreate<GenericLiteralWatcher>()
-      ->RegisterLevelZeroModifiedVariablesCallback(broadcast_level_zero_bounds);
-}
-
-void RegisterVariableBoundsLevelZeroImport(
-    const CpModelProto& model_proto, SharedBoundsManager* shared_bounds_manager,
-    Model* model) {
-  CHECK(shared_bounds_manager != nullptr);
-  auto* integer_trail = model->GetOrCreate<IntegerTrail>();
-  const WorkerInfo* const worker_info = model->GetOrCreate<WorkerInfo>();
-  CpModelMapping* const mapping = model->GetOrCreate<CpModelMapping>();
-
-  const auto& import_level_zero_bounds = [&model_proto, shared_bounds_manager,
-                                          model, integer_trail, worker_info,
-                                          mapping]() {
-    std::vector<int> model_variables;
-    std::vector<int64> new_lower_bounds;
-    std::vector<int64> new_upper_bounds;
-    shared_bounds_manager->GetChangedBounds(worker_info->worker_id,
-                                            &model_variables, &new_lower_bounds,
-                                            &new_upper_bounds);
-    bool new_bounds_have_been_imported = false;
-    for (int i = 0; i < model_variables.size(); ++i) {
-      const int model_var = model_variables[i];
-      // This can happen if a boolean variables is forced to have an
-      // integer view in one thread, and not in another thread.
-      if (!mapping->IsInteger(model_var)) continue;
-      const IntegerVariable var = mapping->Integer(model_var);
-      const IntegerValue new_lb(new_lower_bounds[i]);
-      const IntegerValue new_ub(new_upper_bounds[i]);
-      const IntegerValue old_lb = integer_trail->LowerBound(var);
-      const IntegerValue old_ub = integer_trail->UpperBound(var);
-      const bool changed_lb = new_lb > old_lb;
-      const bool changed_ub = new_ub < old_ub;
-      if (!changed_lb && !changed_ub) continue;
-
-      new_bounds_have_been_imported = true;
-      if (VLOG_IS_ON(2)) {
-        const IntegerVariableProto& var_proto =
-            model_proto.variables(model_var);
-        const std::string& var_name =
-            var_proto.name().empty()
-                ? absl::StrCat("anonymous_var(", model_var, ")")
-                : var_proto.name();
-        LOG(INFO) << "  '" << worker_info->worker_name
-                  << "' imports new bounds for " << var_name << ": from ["
-                  << old_lb << ", " << old_ub << "] to [" << new_lb << ", "
-                  << new_ub << "]";
-      }
-
-      if (changed_lb &&
-          !integer_trail->Enqueue(IntegerLiteral::GreaterOrEqual(var, new_lb),
-                                  {}, {})) {
-        return false;
-      }
-      if (changed_ub &&
-          !integer_trail->Enqueue(IntegerLiteral::LowerOrEqual(var, new_ub), {},
-                                  {})) {
-        return false;
-      }
-    }
-    if (new_bounds_have_been_imported &&
-        !model->GetOrCreate<SatSolver>()->FinishPropagation()) {
-      return false;
-    }
-    return true;
-  };
-  model->GetOrCreate<LevelZeroCallbackHelper>()->callbacks.push_back(
-      import_level_zero_bounds);
-}
-
-void RegisterObjectiveBestBoundExport(
-    IntegerVariable objective_var,
-    SharedResponseManager* shared_response_manager, Model* model) {
-  std::string worker_name = model->GetOrCreate<WorkerInfo>()->worker_name;
-  auto* integer_trail = model->Get<IntegerTrail>();
-  const auto broadcast_objective_lower_bound =
-      [worker_name, objective_var, integer_trail,
-       shared_response_manager](const std::vector<IntegerVariable>& unused) {
-        shared_response_manager->UpdateInnerObjectiveBounds(
-            worker_name, integer_trail->LevelZeroLowerBound(objective_var),
-            integer_trail->LevelZeroUpperBound(objective_var));
-      };
-  model->GetOrCreate<GenericLiteralWatcher>()
-      ->RegisterLevelZeroModifiedVariablesCallback(
-          broadcast_objective_lower_bound);
-}
-
-void RegisterObjectiveBoundsImport(
-    SharedResponseManager* shared_response_manager, Model* model) {
-  auto* solver = model->GetOrCreate<SatSolver>();
-  auto* integer_trail = model->GetOrCreate<IntegerTrail>();
-  auto* worker_info = model->GetOrCreate<WorkerInfo>();
-  auto* objective = model->GetOrCreate<ObjectiveDefinition>();
-  const auto import_objective_bounds = [solver, integer_trail, worker_info,
-                                        objective, shared_response_manager]() {
-    if (solver->AssumptionLevel() != 0) return true;
-    bool propagate = false;
-
-    const IntegerValue external_lb =
-        shared_response_manager->GetInnerObjectiveLowerBound();
-    const IntegerValue current_lb =
-        integer_trail->LowerBound(objective->objective_var);
-    if (external_lb > current_lb) {
-      if (!integer_trail->Enqueue(IntegerLiteral::GreaterOrEqual(
-                                      objective->objective_var, external_lb),
-                                  {}, {})) {
-        return false;
-      }
-      propagate = true;
-    }
-
-    const IntegerValue external_ub =
-        shared_response_manager->GetInnerObjectiveUpperBound();
-    const IntegerValue current_ub =
-        integer_trail->UpperBound(objective->objective_var);
-    if (external_ub < current_ub) {
-      if (!integer_trail->Enqueue(IntegerLiteral::LowerOrEqual(
-                                      objective->objective_var, external_ub),
-                                  {}, {})) {
-        return false;
-      }
-      propagate = true;
-    }
-
-    if (!propagate) return true;
-
-    VLOG(1) << "'" << worker_info->worker_name
-            << "' imports objective bounds: external ["
-            << objective->ScaleIntegerObjective(external_lb) << ", "
-            << objective->ScaleIntegerObjective(external_ub) << "], current ["
-            << objective->ScaleIntegerObjective(current_lb) << ", "
-            << objective->ScaleIntegerObjective(current_ub) << "]";
-
-    return solver->FinishPropagation();
-  };
-
-  model->GetOrCreate<LevelZeroCallbackHelper>()->callbacks.push_back(
-      import_objective_bounds);
-}
-
 }  // namespace sat
 }  // namespace operations_research
diff --git a/ortools/sat/synchronization.h b/ortools/sat/synchronization.h
index fd1beef524..3a6ee8edc1 100644
--- a/ortools/sat/synchronization.h
+++ b/ortools/sat/synchronization.h
@@ -211,31 +211,6 @@ class SharedBoundsManager {
   absl::Mutex mutex_;
 };
 
-// Registers a callback to import new variables bounds stored in the
-// shared_bounds_manager. These bounds are imported at level 0 of the search
-// in the linear scan minimize function.
-void RegisterVariableBoundsLevelZeroImport(
-    const CpModelProto& model_proto, SharedBoundsManager* shared_bounds_manager,
-    Model* model);
-
-// Registers a callback that will export variables bounds fixed at level 0 of
-// the search. This should not be registered to a LNS search.
-void RegisterVariableBoundsLevelZeroExport(
-    const CpModelProto& model_proto, SharedBoundsManager* shared_bounds_manager,
-    Model* model);
-
-// Registers a callback to import new objective bounds. It will be called each
-// time the search main loop is back to level zero. Note that it the presence of
-// assumptions, this will not happend until the set of assumptions is changed.
-void RegisterObjectiveBoundsImport(
-    SharedResponseManager* shared_response_manager, Model* model);
-
-// Registers a callback that will report improving objective best bound.
-// It will be called each time new objective bound are propagated at level zero.
-void RegisterObjectiveBestBoundExport(
-    IntegerVariable objective_var,
-    SharedResponseManager* shared_response_manager, Model* model);
-
 // Stores information on the worker in the parallel context.
 struct WorkerInfo {
   std::string worker_name;