diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index 4f9d29bdd..630998f95 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -4,7 +4,7 @@ on: [push, pull_request]
 
 jobs:
   build:
-    name: ${{matrix.os}}-${{matrix.build_type}}-${{matrix.lib}}-${{matrix.threading_model}}
+    name: ${{matrix.os}}-${{matrix.build_type}}-${{matrix.lib}}
     runs-on: ubuntu-latest
     container: ${{matrix.os}}
     defaults:
@@ -25,10 +25,6 @@ jobs:
         lib:
           - shared
           - static
-        threading_model:
-          - CXX_THREADS
-          - NO_THREADS
-          - OPENMP
 
     steps:
       - uses: actions/checkout@v2
@@ -55,8 +51,8 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ${{env.CCACHE_DIR}}
-          key: ${{matrix.os}}-ccache-${{matrix.build_type}}-${{matrix.lib}}-${{matrix.threading_model}}-${{github.run_id}}
-          restore-keys: ${{matrix.os}}-ccache-${{matrix.build_type}}-${{matrix.lib}}-${{matrix.threading_model}}-
+          key: ${{matrix.os}}-ccache-${{matrix.build_type}}-${{matrix.lib}}-${{github.run_id}}
+          restore-keys: ${{matrix.os}}-ccache-${{matrix.build_type}}-${{matrix.lib}}-
 
       - name: Setup Environment
         if: matrix.build_type == 'Release'
@@ -67,7 +63,6 @@ jobs:
         run: |
           cmake -S . -B build_${{matrix.build_type}} \
                 -DBUILD_SHARED_LIBS=${{matrix.lib == 'shared'}} \
-                -DCERES_THREADING_MODEL=${{matrix.threading_model}} \
                 -DCMAKE_BUILD_TYPE=${{matrix.build_type}} \
                 -DCMAKE_C_COMPILER_LAUNCHER=$(which ccache) \
                 -DCMAKE_CXX_COMPILER_LAUNCHER=$(which ccache) \
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 01f47b815..c30ae9ffb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -118,24 +118,9 @@ read_ceres_version_from_source(${Ceres_SOURCE_DIR})
 
 enable_testing()
 
-include(CeresThreadingModels)
 include(CMakeDependentOption)
 include(PrettyPrintCMakeList)
 
-find_available_ceres_threading_models(CERES_THREADING_MODELS_AVAILABLE)
-pretty_print_cmake_list(PRETTY_CERES_THREADING_MODELS_AVAILABLE
-  ${CERES_THREADING_MODELS_AVAILABLE})
-message("-- Detected available Ceres threading models: "
-  "${PRETTY_CERES_THREADING_MODELS_AVAILABLE}")
-set(CERES_THREADING_MODEL "${CERES_THREADING_MODEL}" CACHE STRING
-  "Ceres threading back-end" FORCE)
-if (NOT CERES_THREADING_MODEL)
-  list(GET CERES_THREADING_MODELS_AVAILABLE 0 DEFAULT_THREADING_MODEL)
-  update_cache_variable(CERES_THREADING_MODEL ${DEFAULT_THREADING_MODEL})
-endif()
-set_property(CACHE CERES_THREADING_MODEL PROPERTY STRINGS
-  ${CERES_THREADING_MODELS_AVAILABLE})
-
 option(MINIGLOG "Use a stripped down version of glog." OFF)
 option(GFLAGS "Enable Google Flags." ON)
 option(SUITESPARSE "Enable SuiteSparse." ON)
@@ -197,8 +182,8 @@ if (IOS)
   # Apple claims that the BLAS call dsyrk_ is a private API, and will not allow
   # you to submit to the Apple Store if the symbol is present.
   update_cache_variable(LAPACK OFF)
-  message(STATUS "Building for iOS: SuiteSparse, LAPACK, gflags, "
-    "and OpenMP are not available.")
+  message(STATUS "Building for iOS: SuiteSparse, LAPACK, gflags "
+    "are not available.")
 
   update_cache_variable(BUILD_EXAMPLES OFF)
   message(STATUS "Building for iOS: Will not build examples.")
@@ -489,8 +474,6 @@ if (NOT CUSTOM_BLAS)
   message("-- Disabling custom blas")
 endif (NOT CUSTOM_BLAS)
 
-set_ceres_threading_model("${CERES_THREADING_MODEL}")
-
 if (BUILD_BENCHMARKS)
   # Version 1.3 was first to provide import targets
   find_package(benchmark 1.3 QUIET)
diff --git a/cmake/CeresCompileOptionsToComponents.cmake b/cmake/CeresCompileOptionsToComponents.cmake
index 0baf2147b..47b0f2af5 100644
--- a/cmake/CeresCompileOptionsToComponents.cmake
+++ b/cmake/CeresCompileOptionsToComponents.cmake
@@ -80,10 +80,6 @@ function(ceres_compile_options_to_components CURRENT_CERES_COMPILE_OPTIONS CERES
     CERES_NO_ACCELERATE_SPARSE "AccelerateSparse;SparseLinearAlgebraLibrary")
   add_to_output_if_not_found(CURRENT_CERES_COMPILE_OPTIONS ${CERES_COMPONENTS_VAR}
     CERES_RESTRICT_SCHUR_SPECIALIZATION "SchurSpecializations")
-  add_to_output_if_found(CURRENT_CERES_COMPILE_OPTIONS ${CERES_COMPONENTS_VAR}
-    CERES_USE_OPENMP "OpenMP;Multithreading")
-  add_to_output_if_found(CURRENT_CERES_COMPILE_OPTIONS ${CERES_COMPONENTS_VAR}
-    CERES_USE_CXX_THREADS "Multithreading")
   # Remove duplicates of SparseLinearAlgebraLibrary if multiple sparse backends
   # are present.
   list(REMOVE_DUPLICATES ${CERES_COMPONENTS_VAR})
diff --git a/cmake/CeresConfig.cmake.in b/cmake/CeresConfig.cmake.in
index bb6cc43a1..ceb7e269c 100644
--- a/cmake/CeresConfig.cmake.in
+++ b/cmake/CeresConfig.cmake.in
@@ -178,10 +178,9 @@ set(CERES_VERSION @CERES_VERSION@)
 include(CMakeFindDependencyMacro)
 # Optional dependencies
 @METIS_DEPENDENCY@
-@OpenMP_DEPENDENCY@
 @SuiteSparse_DEPENDENCY@
-@Threads_DEPENDENCY@
 @CUDAToolkit_DEPENDENCY@
+@Threads_DEPENDENCY@
 
 # As imported CMake targets are not re-exported when a dependent target is
 # exported, we must invoke find_package(XXX) here to reload the definition
diff --git a/cmake/CeresThreadingModels.cmake b/cmake/CeresThreadingModels.cmake
deleted file mode 100644
index 571dd7d50..000000000
--- a/cmake/CeresThreadingModels.cmake
+++ /dev/null
@@ -1,82 +0,0 @@
-# Ceres Solver - A fast non-linear least squares minimizer
-# Copyright 2018 Google Inc. All rights reserved.
-# http://ceres-solver.org/
-#
-# Redistribution and use in source and binary forms, with or without
-# modification, are permitted provided that the following conditions are met:
-#
-# * Redistributions of source code must retain the above copyright notice,
-#   this list of conditions and the following disclaimer.
-# * Redistributions in binary form must reproduce the above copyright notice,
-#   this list of conditions and the following disclaimer in the documentation
-#   and/or other materials provided with the distribution.
-# * Neither the name of Google Inc. nor the names of its contributors may be
-#   used to endorse or promote products derived from this software without
-#   specific prior written permission.
-#
-# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
-# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-# POSSIBILITY OF SUCH DAMAGE.
-#
-# Author: alexs.mac@gmail.com (Alex Stewart)
-
-# Ordered by expected preference.
-set(CERES_THREADING_MODELS "CXX_THREADS;OPENMP;NO_THREADS")
-
-function(find_available_ceres_threading_models CERES_THREADING_MODELS_AVAILABLE_VAR)
-  set(CERES_THREADING_MODELS_AVAILABLE ${CERES_THREADING_MODELS})
-  # Remove any threading models for which the dependencies are not available.
-  find_package(OpenMP QUIET)
-  if (NOT OPENMP_FOUND)
-    list(REMOVE_ITEM CERES_THREADING_MODELS_AVAILABLE "OPENMP")
-  endif()
-  if (NOT CERES_THREADING_MODELS_AVAILABLE)
-    # At least NO_THREADS should never be removed.  This check is purely
-    # protective against future threading model updates.
-    message(FATAL_ERROR "Ceres bug: Removed all threading models.")
-  endif()
-  set(${CERES_THREADING_MODELS_AVAILABLE_VAR}
-    ${CERES_THREADING_MODELS_AVAILABLE} PARENT_SCOPE)
-endfunction()
-
-macro(set_ceres_threading_model_to_cxx11_threads)
-  list(APPEND CERES_COMPILE_OPTIONS CERES_USE_CXX_THREADS)
-endmacro()
-
-macro(set_ceres_threading_model_to_openmp)
-  find_package(OpenMP REQUIRED)
-  list(APPEND CERES_COMPILE_OPTIONS CERES_USE_OPENMP)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
-endmacro()
-
-macro(set_ceres_threading_model_to_no_threads)
-  list(APPEND CERES_COMPILE_OPTIONS CERES_NO_THREADS)
-endmacro()
-
-macro(set_ceres_threading_model CERES_THREADING_MODEL_TO_SET)
-  if ("${CERES_THREADING_MODEL_TO_SET}" STREQUAL "CXX_THREADS")
-    set_ceres_threading_model_to_cxx11_threads()
-  elseif ("${CERES_THREADING_MODEL_TO_SET}" STREQUAL "OPENMP")
-    set_ceres_threading_model_to_openmp()
-  elseif ("${CERES_THREADING_MODEL_TO_SET}" STREQUAL "NO_THREADS")
-    set_ceres_threading_model_to_no_threads()
-  else()
-    include(PrettyPrintCMakeList)
-    find_available_ceres_threading_models(_AVAILABLE_THREADING_MODELS)
-    pretty_print_cmake_list(
-      _AVAILABLE_THREADING_MODELS ${_AVAILABLE_THREADING_MODELS})
-    message(FATAL_ERROR "Unknown threading model specified: "
-      "'${CERES_THREADING_MODEL_TO_SET}'. Available threading models for "
-      "this platform are: ${_AVAILABLE_THREADING_MODELS}")
-  endif()
-  message("-- Using Ceres threading model: ${CERES_THREADING_MODEL_TO_SET}")
-endmacro()
diff --git a/cmake/config.h.in b/cmake/config.h.in
index 40079550f..0e7fd3a9e 100644
--- a/cmake/config.h.in
+++ b/cmake/config.h.in
@@ -70,12 +70,6 @@
 // routines.
 @CERES_NO_CUSTOM_BLAS@
 
-// If defined, Ceres was compiled without multithreading support.
-@CERES_NO_THREADS@
-// If defined Ceres was compiled with OpenMP multithreading.
-@CERES_USE_OPENMP@
-// If defined Ceres was compiled with modern C++ multithreading.
-@CERES_USE_CXX_THREADS@
 // If defined, Ceres was compiled with a version of SuiteSparse/CHOLMOD without
 // the Partition module (requires METIS).
 @CERES_NO_CHOLMOD_PARTITION@
@@ -87,22 +81,6 @@
 // with underscore prefixed versions (e.g. j0() -> _j0()).
 @CERES_MSVC_USE_UNDERSCORE_PREFIXED_BESSEL_FUNCTIONS@
 
-#if defined(CERES_USE_OPENMP)
-#if defined(CERES_USE_CXX_THREADS) || defined(CERES_NO_THREADS)
-#error CERES_USE_OPENMP is mutually exclusive to CERES_USE_CXX_THREADS and CERES_NO_THREADS
-#endif
-#elif defined(CERES_USE_CXX_THREADS)
-#if defined(CERES_USE_OPENMP) || defined(CERES_NO_THREADS)
-#error CERES_USE_CXX_THREADS is mutually exclusive to CERES_USE_OPENMP, CERES_USE_CXX_THREADS and CERES_NO_THREADS
-#endif
-#elif defined(CERES_NO_THREADS)
-#if defined(CERES_USE_OPENMP) || defined(CERES_USE_CXX_THREADS)
-#error CERES_NO_THREADS is mutually exclusive to CERES_USE_OPENMP and CERES_USE_CXX_THREADS
-#endif
-#else
-#  error One of CERES_USE_OPENMP, CERES_USE_CXX_THREADS or CERES_NO_THREADS must be defined.
-#endif
-
 // CERES_NO_SPARSE should be automatically defined by config.h if Ceres was
 // compiled without any sparse back-end.  Verify that it has not subsequently
 // been inconsistently redefined.
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index 06c091497..1e6a69951 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -32,25 +32,10 @@
 
 # Avoid 'xxx.cc has no symbols' warnings from source files which are 'empty'
 # when their enclosing #ifdefs are disabled.
-if (CERES_THREADING_MODEL STREQUAL "CXX_THREADS")
-  set(CERES_PARALLEL_FOR_SRC parallel_for_cxx.cc thread_pool.cc)
-  find_package(Threads REQUIRED)
-  list(APPEND CERES_LIBRARY_PRIVATE_DEPENDENCIES Threads::Threads)
-
-  # Make dependency visible to the parent CMakeLists.txt
-  set(Threads_DEPENDENCY "find_dependency (Threads)" PARENT_SCOPE)
-elseif (CERES_THREADING_MODEL STREQUAL "OPENMP")
-  # OpenMP requires linking to the corresponding library.
-  find_package(OpenMP REQUIRED COMPONENTS CXX)
-
-  set(CERES_PARALLEL_FOR_SRC parallel_for_openmp.cc)
-  list(APPEND CERES_LIBRARY_PRIVATE_DEPENDENCIES OpenMP::OpenMP_CXX)
-
-  # Make dependency visible to the parent CMakeLists.txt
-  set(OpenMP_DEPENDENCY "find_dependency (OpenMP ${OpenMP_CXX_VERSION} COMPONENTS CXX)" PARENT_SCOPE)
-elseif (CERES_THREADING_MODEL STREQUAL "NO_THREADS")
-  set(CERES_PARALLEL_FOR_SRC parallel_for_nothreads.cc)
-endif()
+find_package(Threads REQUIRED)
+list(APPEND CERES_LIBRARY_PRIVATE_DEPENDENCIES Threads::Threads)
+# Make dependency visible to the parent CMakeLists.txt
+set(Threads_DEPENDENCY "find_dependency (Threads)" PARENT_SCOPE)
 
 # Source files that contain public symbols and live in the ceres namespaces.
 # Such symbols are expected to be marked with CERES_EXPORT and the files below
@@ -171,7 +156,6 @@ endif ()
 # lexicographical order.
 add_library(ceres_internal OBJECT
     ${CERES_INTERNAL_SCHUR_FILES}
-    ${CERES_PARALLEL_FOR_SRC}
     accelerate_sparse.cc
     array_utils.cc
     block_evaluate_preparer.cc
@@ -235,6 +219,7 @@ add_library(ceres_internal OBJECT
     linear_solver.cc
     low_rank_inverse_hessian.cc
     minimizer.cc
+    parallel_for_cxx.cc
     parallel_utils.cc
     parameter_block_ordering.cc
     partitioned_matrix_view.cc
@@ -260,6 +245,7 @@ add_library(ceres_internal OBJECT
     stringprintf.cc
     subset_preconditioner.cc
     suitesparse.cc
+    thread_pool.cc
     thread_token_provider.cc
     triplet_sparse_matrix.cc
     trust_region_minimizer.cc
diff --git a/internal/ceres/concurrent_queue_test.cc b/internal/ceres/concurrent_queue_test.cc
index b0930fe95..08451bdea 100644
--- a/internal/ceres/concurrent_queue_test.cc
+++ b/internal/ceres/concurrent_queue_test.cc
@@ -28,15 +28,12 @@
 //
 // Author: vitus@google.com (Michael Vitus)
 
-// This include must come before any #ifndef check on Ceres compile options.
-#include "ceres/internal/config.h"
-
-#ifdef CERES_USE_CXX_THREADS
+#include "ceres/concurrent_queue.h"
 
 #include <chrono>
 #include <thread>
 
-#include "ceres/concurrent_queue.h"
+#include "ceres/internal/config.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
@@ -300,5 +297,3 @@ TEST(ConcurrentQueue, StopAndEnableWaiters) {
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/context_impl.cc b/internal/ceres/context_impl.cc
index 56c978557..cc01b5436 100644
--- a/internal/ceres/context_impl.cc
+++ b/internal/ceres/context_impl.cc
@@ -171,9 +171,9 @@ ContextImpl::~ContextImpl() {
   TearDown();
 #endif  // CERES_NO_CUDA
 }
+
 void ContextImpl::EnsureMinimumThreads(int num_threads) {
-#ifdef CERES_USE_CXX_THREADS
   thread_pool.Resize(num_threads);
-#endif  // CERES_USE_CXX_THREADS
 }
+
 }  // namespace ceres::internal
diff --git a/internal/ceres/context_impl.h b/internal/ceres/context_impl.h
index d8f294ace..a18d6388f 100644
--- a/internal/ceres/context_impl.h
+++ b/internal/ceres/context_impl.h
@@ -49,9 +49,7 @@
 #include "cusparse.h"
 #endif  // CERES_NO_CUDA
 
-#ifdef CERES_USE_CXX_THREADS
 #include "ceres/thread_pool.h"
-#endif  // CERES_USE_CXX_THREADS
 
 namespace ceres::internal {
 
@@ -67,9 +65,7 @@ class CERES_NO_EXPORT ContextImpl final : public Context {
   // defined by the hardware.  Otherwise this call is a no-op.
   void EnsureMinimumThreads(int num_threads);
 
-#ifdef CERES_USE_CXX_THREADS
   ThreadPool thread_pool;
-#endif  // CERES_USE_CXX_THREADS
 
 #ifndef CERES_NO_CUDA
   // Note on Ceres' use of CUDA Devices on multi-GPU systems:
diff --git a/internal/ceres/covariance_impl.cc b/internal/ceres/covariance_impl.cc
index 9957d1d2d..5d8b87f68 100644
--- a/internal/ceres/covariance_impl.cc
+++ b/internal/ceres/covariance_impl.cc
@@ -65,15 +65,6 @@ using CovarianceBlocks = std::vector<std::pair<const double*, const double*>>;
 
 CovarianceImpl::CovarianceImpl(const Covariance::Options& options)
     : options_(options), is_computed_(false), is_valid_(false) {
-#ifdef CERES_NO_THREADS
-  if (options_.num_threads > 1) {
-    LOG(WARNING) << "No threading support is compiled into this binary; "
-                 << "only options.num_threads = 1 is supported. Switching "
-                 << "to single threaded mode.";
-    options_.num_threads = 1;
-  }
-#endif
-
   evaluate_options_.num_threads = options_.num_threads;
   evaluate_options_.apply_loss_function = options_.apply_loss_function;
 }
diff --git a/internal/ceres/covariance_test.cc b/internal/ceres/covariance_test.cc
index caea18c7e..76fcb122e 100644
--- a/internal/ceres/covariance_test.cc
+++ b/internal/ceres/covariance_test.cc
@@ -639,8 +639,6 @@ TEST_F(CovarianceTest, NormalBehavior) {
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
 }
 
-#ifdef CERES_USE_OPENMP
-
 TEST_F(CovarianceTest, ThreadedNormalBehavior) {
   // J
   //
@@ -691,8 +689,6 @@ TEST_F(CovarianceTest, ThreadedNormalBehavior) {
   ComputeAndCompareCovarianceBlocks(options, expected_covariance);
 }
 
-#endif  // CERES_USE_OPENMP
-
 TEST_F(CovarianceTest, ConstantParameterBlock) {
   problem_.SetParameterBlockConstant(parameters_);
 
@@ -1355,13 +1351,13 @@ class LargeScaleCovarianceTest : public ::testing::Test {
   vector<pair<const double*, const double*>> all_covariance_blocks_;
 };
 
-#if !defined(CERES_NO_SUITESPARSE) && defined(CERES_USE_OPENMP)
+#if !defined(CERES_NO_SUITESPARSE)
 
 TEST_F(LargeScaleCovarianceTest, Parallel) {
   ComputeAndCompare(SPARSE_QR, SUITE_SPARSE, 4);
 }
 
-#endif  // !defined(CERES_NO_SUITESPARSE) && defined(CERES_USE_OPENMP)
+#endif  // !defined(CERES_NO_SUITESPARSE)
 
 }  // namespace internal
 }  // namespace ceres
diff --git a/internal/ceres/generate_bundle_adjustment_tests.py b/internal/ceres/generate_bundle_adjustment_tests.py
index 6e6027085..35865a61c 100644
--- a/internal/ceres/generate_bundle_adjustment_tests.py
+++ b/internal/ceres/generate_bundle_adjustment_tests.py
@@ -221,11 +221,6 @@ def generate_bundle_test(linear_solver,
     preprocessor_conditions_begin.append('#ifndef CERES_NO_CUDA')
     preprocessor_conditions_end.insert(0, '#endif  // CERES_NO_CUDA')
 
-  # Accumulate appropriate #ifdef/#ifndefs for threading conditions.
-  if thread_config == MULTI_THREADED:
-    preprocessor_conditions_begin.append('#ifndef CERES_NO_THREADS')
-    preprocessor_conditions_end.insert(0, '#endif  // CERES_NO_THREADS')
-
   # If there are #ifdefs, put newlines around them.
   if preprocessor_conditions_begin:
     preprocessor_conditions_begin.insert(0, '')
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc
index d0181e38b..c0020c25b 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_CUDA
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CUDA
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc
index ecda17c97..042848a21 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_CUDA
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CUDA
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc
index a355e851d..3c32212b6 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc
@@ -38,8 +38,6 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-#ifndef CERES_NO_THREADS
-
 namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
@@ -59,5 +57,3 @@ TEST_F(BundleAdjustmentTest,
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc
index f005c31d4..9335b8215 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc
@@ -38,8 +38,6 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-#ifndef CERES_NO_THREADS
-
 namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
@@ -59,5 +57,3 @@ TEST_F(BundleAdjustmentTest,
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc
index 4e727dbeb..1acda327c 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_LAPACK
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_LAPACK
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc
index e19734a34..0d39dcd03 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_LAPACK
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_LAPACK
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc
index 93b58ebf1..acb5c1602 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc
index 053e9b236..42570c42c 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc
index 723246a1e..f67030a9c 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc
index 93f5353c2..a638cfed7 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc
index 1e9dbf05b..5adb25a2b 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc
index 0daf51925..d531c340d 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc
index 1ee128652..c82924cc2 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc
index 6e08b2279..f7de34f25 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc
index e0aad4485..4666424cd 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc
@@ -38,8 +38,6 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-#ifndef CERES_NO_THREADS
-
 namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
@@ -59,5 +57,3 @@ TEST_F(BundleAdjustmentTest,
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc
index c68f6f052..09d5bd034 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc
@@ -38,8 +38,6 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-#ifndef CERES_NO_THREADS
-
 namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
@@ -59,5 +57,3 @@ TEST_F(BundleAdjustmentTest,
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc
index 6d97ebab0..beaa92a47 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc
@@ -38,8 +38,6 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-#ifndef CERES_NO_THREADS
-
 namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
@@ -59,5 +57,3 @@ TEST_F(BundleAdjustmentTest,
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc
index 71220f74a..762f8810c 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc
@@ -38,8 +38,6 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-#ifndef CERES_NO_THREADS
-
 namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
@@ -59,5 +57,3 @@ TEST_F(BundleAdjustmentTest,
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc
index 874168db3..e31446a69 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc
index ae07667ae..d26cc333e 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc
index aee5e5a31..35df772e0 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc
index 9bc2d3fb7..e71b4e5c9 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc
index 79769b435..38731ecd6 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc
index 6131f1dc3..27e32d122 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc
index 46e5dac97..6b9372782 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc
index 68f3be7f5..a92ccfbaa 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc
index ef1100577..f8aa16ff9 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc
index 862142a25..09ac24e5a 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc
index 595fc155e..b6b53ce39 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc
index c1302f731..da4c9df49 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc
index 137725bad..7a8bd90c4 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc
index 14dcabf31..35c73ca8f 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifdef CERES_USE_EIGEN_SPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc
index cf015b87b..2cdb888f4 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc
index b13915e70..04f36337b 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc
@@ -39,7 +39,6 @@
 #include "bundle_adjustment_test_util.h"
 
 #ifndef CERES_NO_SUITESPARSE
-#ifndef CERES_NO_THREADS
 
 namespace ceres::internal {
 
@@ -61,5 +60,4 @@ TEST_F(BundleAdjustmentTest,
 
 }  // namespace ceres::internal
 
-#endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/parallel_for.h b/internal/ceres/parallel_for.h
index fe5d242a4..d91a195a6 100644
--- a/internal/ceres/parallel_for.h
+++ b/internal/ceres/parallel_for.h
@@ -338,21 +338,7 @@ void ParallelFor(ContextImpl* context,
 }  // namespace ceres::internal
 
 // Backend-specific implementations of ParallelInvoke
-#include "ceres/parallel_for_cxx.h"
-#include "ceres/parallel_for_openmp.h"
-#ifdef CERES_NO_THREADS
-namespace ceres::internal {
-template <typename F>
-void ParallelInvoke(ContextImpl* context,
-                    int start,
-                    int end,
-                    int num_threads,
-                    const F& function) {
-  ParallelFor(context, start, end, 1, function);
-}
-}  // namespace ceres::internal
-#endif
-
 #include "ceres/internal/disable_warnings.h"
+#include "ceres/parallel_for_cxx.h"
 
 #endif  // CERES_INTERNAL_PARALLEL_FOR_H_
diff --git a/internal/ceres/parallel_for_cxx.cc b/internal/ceres/parallel_for_cxx.cc
index 13cabf90b..cdf9966f5 100644
--- a/internal/ceres/parallel_for_cxx.cc
+++ b/internal/ceres/parallel_for_cxx.cc
@@ -28,17 +28,13 @@
 //
 // Author: vitus@google.com (Michael Vitus)
 
-// This include must come before any #ifndef check on Ceres compile options.
-#include "ceres/internal/config.h"
-
-#ifdef CERES_USE_CXX_THREADS
-
 #include <atomic>
 #include <cmath>
 #include <condition_variable>
 #include <memory>
 #include <mutex>
 
+#include "ceres/internal/config.h"
 #include "ceres/parallel_for.h"
 #include "glog/logging.h"
 
@@ -79,5 +75,3 @@ ThreadPoolState::ThreadPoolState(int start,
 int MaxNumThreadsAvailable() { return ThreadPool::MaxNumThreadsAvailable(); }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/parallel_for_cxx.h b/internal/ceres/parallel_for_cxx.h
index b745a6407..073160992 100644
--- a/internal/ceres/parallel_for_cxx.h
+++ b/internal/ceres/parallel_for_cxx.h
@@ -29,21 +29,16 @@
 // Authors: vitus@google.com (Michael Vitus),
 //          dmitriy.korchemkin@gmail.com (Dmitriy Korchemkin)
 
-// This include must come before any #ifndef check on Ceres compile options.
 #ifndef CERES_INTERNAL_PARALLEL_FOR_CXX_H_
 #define CERES_INTERNAL_PARALLEL_FOR_CXX_H_
 
-// This include must come before any #ifndef check on Ceres compile options.
-#include "ceres/internal/config.h"
-
-#ifdef CERES_USE_CXX_THREADS
-
 #include <atomic>
 #include <cmath>
 #include <condition_variable>
 #include <memory>
 #include <mutex>
 
+#include "ceres/internal/config.h"
 #include "glog/logging.h"
 
 namespace ceres::internal {
@@ -243,6 +238,7 @@ void ParallelInvoke(ContextImpl* context,
   // Wait until all tasks have finished.
   shared_state->block_until_finished.Block();
 }
+
 }  // namespace ceres::internal
-#endif
-#endif
+
+#endif  // CERES_INTERNAL_PARALLEL_FOR_CXX_H_
diff --git a/internal/ceres/parallel_for_nothreads.cc b/internal/ceres/parallel_for_nothreads.cc
deleted file mode 100644
index 8d3611dbc..000000000
--- a/internal/ceres/parallel_for_nothreads.cc
+++ /dev/null
@@ -1,47 +0,0 @@
-// Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2018 Google Inc. All rights reserved.
-// http://ceres-solver.org/
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are met:
-//
-// * Redistributions of source code must retain the above copyright notice,
-//   this list of conditions and the following disclaimer.
-// * Redistributions in binary form must reproduce the above copyright notice,
-//   this list of conditions and the following disclaimer in the documentation
-//   and/or other materials provided with the distribution.
-// * Neither the name of Google Inc. nor the names of its contributors may be
-//   used to endorse or promote products derived from this software without
-//   specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
-// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-// POSSIBILITY OF SUCH DAMAGE.
-//
-// Author: alexs.mac@gmail.com (Alex Stewart)
-
-// This include must come before any #ifndef check on Ceres compile options.
-#include "ceres/internal/config.h"
-
-#ifdef CERES_NO_THREADS
-
-#include "ceres/parallel_for.h"
-#include "glog/logging.h"
-
-namespace ceres {
-namespace internal {
-
-int MaxNumThreadsAvailable() { return 1; }
-
-}  // namespace internal
-}  // namespace ceres
-
-#endif  // CERES_NO_THREADS
diff --git a/internal/ceres/parallel_for_openmp.cc b/internal/ceres/parallel_for_openmp.cc
deleted file mode 100644
index 02690f310..000000000
--- a/internal/ceres/parallel_for_openmp.cc
+++ /dev/null
@@ -1,48 +0,0 @@
-// Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2018 Google Inc. All rights reserved.
-// http://ceres-solver.org/
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are met:
-//
-// * Redistributions of source code must retain the above copyright notice,
-//   this list of conditions and the following disclaimer.
-// * Redistributions in binary form must reproduce the above copyright notice,
-//   this list of conditions and the following disclaimer in the documentation
-//   and/or other materials provided with the distribution.
-// * Neither the name of Google Inc. nor the names of its contributors may be
-//   used to endorse or promote products derived from this software without
-//   specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
-// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-// POSSIBILITY OF SUCH DAMAGE.
-//
-// Author: vitus@google.com (Michael Vitus)
-
-// This include must come before any #ifndef check on Ceres compile options.
-#include "ceres/internal/config.h"
-
-#if defined(CERES_USE_OPENMP)
-
-#include "ceres/parallel_for.h"
-#include "glog/logging.h"
-#include "omp.h"
-
-namespace ceres {
-namespace internal {
-
-int MaxNumThreadsAvailable() { return omp_get_max_threads(); }
-
-}  // namespace internal
-}  // namespace ceres
-
-#endif  // defined(CERES_USE_OPENMP)
diff --git a/internal/ceres/parallel_for_openmp.h b/internal/ceres/parallel_for_openmp.h
deleted file mode 100644
index 94254c455..000000000
--- a/internal/ceres/parallel_for_openmp.h
+++ /dev/null
@@ -1,70 +0,0 @@
-// Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2018 Google Inc. All rights reserved.
-// http://ceres-solver.org/
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are met:
-//
-// * Redistributions of source code must retain the above copyright notice,
-//   this list of conditions and the following disclaimer.
-// * Redistributions in binary form must reproduce the above copyright notice,
-//   this list of conditions and the following disclaimer in the documentation
-//   and/or other materials provided with the distribution.
-// * Neither the name of Google Inc. nor the names of its contributors may be
-//   used to endorse or promote products derived from this software without
-//   specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
-// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-// POSSIBILITY OF SUCH DAMAGE.
-//
-// Authors: vitus@google.com (Michael Vitus),
-//          dmitriy.korchemkin@gmail.com (Dmitriy Korchemkin)
-
-// This include must come before any #ifndef check on Ceres compile options.
-#ifndef CERES_INTERNAL_PARALLEL_FOR_OPENMP_H_
-#define CERES_INTERNAL_PARALLEL_FOR_OPENMP_H_
-
-#include "ceres/internal/config.h"
-
-#if defined(CERES_USE_OPENMP)
-
-#include "ceres/parallel_for.h"
-#include "ceres/scoped_thread_token.h"
-#include "ceres/thread_token_provider.h"
-#include "glog/logging.h"
-#include "omp.h"
-
-namespace ceres::internal {
-
-template <typename F>
-void ParallelInvoke(ContextImpl* context,
-                    int start,
-                    int end,
-                    int num_threads,
-                    const F& function) {
-  using namespace parallel_for_details;
-  ThreadTokenProvider token_provider(num_threads);
-#pragma omp parallel num_threads(num_threads)
-  {
-    const ScopedThreadToken scoped_thread_token(&token_provider);
-    const int thread_id = scoped_thread_token.token();
-#pragma omp for schedule(guided)
-    for (int i = start; i < end; ++i) {
-      Invoke<F>(thread_id, i, function);
-    }
-  }
-}
-
-}  // namespace ceres::internal
-
-#endif
-#endif
diff --git a/internal/ceres/parallel_for_test.cc b/internal/ceres/parallel_for_test.cc
index 54ca63683..6974ab903 100644
--- a/internal/ceres/parallel_for_test.cc
+++ b/internal/ceres/parallel_for_test.cc
@@ -28,11 +28,6 @@
 //
 // Author: vitus@google.com (Michael Vitus)
 
-// This include must come before any #ifndef check on Ceres compile options.
-// clang-format off
-#include "ceres/internal/config.h"
-// clang-format on
-
 #include "ceres/parallel_for.h"
 
 #include <cmath>
@@ -44,6 +39,7 @@
 #include <vector>
 
 #include "ceres/context_impl.h"
+#include "ceres/internal/config.h"
 #include "glog/logging.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
@@ -133,8 +129,6 @@ TEST(ParallelForWithThreadId, NestedParallelForDeadlock) {
   }
 }
 
-// This test is only valid when multithreading support is enabled.
-#ifndef CERES_NO_THREADS
 TEST(ParallelForWithThreadId, UniqueThreadIds) {
   // Ensure the hardware supports more than 1 thread to ensure the test will
   // pass.
@@ -166,7 +160,6 @@ TEST(ParallelForWithThreadId, UniqueThreadIds) {
 
   EXPECT_THAT(x, UnorderedElementsAreArray({0, 1}));
 }
-#endif  // CERES_NO_THREADS
 
 // Helper function for partition tests
 bool BruteForcePartition(
diff --git a/internal/ceres/parallel_utils_test.cc b/internal/ceres/parallel_utils_test.cc
index fd2d79246..1facb3e25 100644
--- a/internal/ceres/parallel_utils_test.cc
+++ b/internal/ceres/parallel_utils_test.cc
@@ -28,13 +28,9 @@
 //
 // Author: wjr@google.com (William Rucklidge)
 
-// This include must come before any #ifndef check on Ceres compile options.
-// clang-format off
-#include "ceres/internal/config.h"
-// clang-format on
-
 #include "ceres/parallel_utils.h"
 
+#include "ceres/internal/config.h"
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
diff --git a/internal/ceres/problem_impl.cc b/internal/ceres/problem_impl.cc
index 326416649..4440526fb 100644
--- a/internal/ceres/problem_impl.cc
+++ b/internal/ceres/problem_impl.cc
@@ -672,17 +672,7 @@ bool ProblemImpl::Evaluate(const Problem::EvaluateOptions& evaluate_options,
   // the Evaluator decides the storage for the Jacobian based on the
   // type of linear solver being used.
   evaluator_options.linear_solver_type = SPARSE_NORMAL_CHOLESKY;
-#ifdef CERES_NO_THREADS
-  if (evaluate_options.num_threads > 1) {
-    LOG(WARNING)
-        << "No threading support is compiled into this binary; "
-        << "only evaluate_options.num_threads = 1 is supported. Switching "
-        << "to single threaded mode.";
-  }
-  evaluator_options.num_threads = 1;
-#else
   evaluator_options.num_threads = evaluate_options.num_threads;
-#endif  // CERES_NO_THREADS
 
   // The main thread also does work so we only need to launch num_threads - 1.
   context_impl_->EnsureMinimumThreads(evaluator_options.num_threads - 1);
diff --git a/internal/ceres/program_evaluator.h b/internal/ceres/program_evaluator.h
index 1176bb860..251a17704 100644
--- a/internal/ceres/program_evaluator.h
+++ b/internal/ceres/program_evaluator.h
@@ -119,15 +119,6 @@ class ProgramEvaluator final : public Evaluator {
         jacobian_writer_(options, program),
         evaluate_preparers_(std::move(
             jacobian_writer_.CreateEvaluatePreparers(options.num_threads))) {
-#ifdef CERES_NO_THREADS
-    if (options_.num_threads > 1) {
-      LOG(WARNING) << "No threading support is compiled into this binary; "
-                   << "only options.num_threads = 1 is supported. Switching "
-                   << "to single threaded mode.";
-      options_.num_threads = 1;
-    }
-#endif  // CERES_NO_THREADS
-
     BuildResidualLayout(*program, &residual_layout_);
     evaluate_scratch_ = std::move(CreateEvaluatorScratch(
         *program, static_cast<unsigned>(options.num_threads)));
diff --git a/internal/ceres/solver_utils.cc b/internal/ceres/solver_utils.cc
index 4c4a354ae..de1c38b47 100644
--- a/internal/ceres/solver_utils.cc
+++ b/internal/ceres/solver_utils.cc
@@ -78,12 +78,6 @@ constexpr char kVersion[] =
   "-no_schur_specializations"
 #endif
 
-#ifdef CERES_USE_OPENMP
-  "-openmp"
-#else
-  "-no_openmp"
-#endif
-
 #ifdef CERES_NO_CUSTOM_BLAS
   "-no_custom_blas"
 #endif
diff --git a/internal/ceres/thread_pool.cc b/internal/ceres/thread_pool.cc
index 1fd1a4caf..16b86e1f8 100644
--- a/internal/ceres/thread_pool.cc
+++ b/internal/ceres/thread_pool.cc
@@ -28,15 +28,12 @@
 //
 // Author: vitus@google.com (Michael Vitus)
 
-// This include must come before any #ifndef check on Ceres compile options.
-#include "ceres/internal/config.h"
-
-#ifdef CERES_USE_CXX_THREADS
+#include "ceres/thread_pool.h"
 
 #include <cmath>
 #include <limits>
 
-#include "ceres/thread_pool.h"
+#include "ceres/internal/config.h"
 
 namespace ceres::internal {
 namespace {
@@ -105,5 +102,3 @@ void ThreadPool::ThreadMainLoop() {
 void ThreadPool::Stop() { task_queue_.StopWaiters(); }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/thread_pool_test.cc b/internal/ceres/thread_pool_test.cc
index e64011db8..63b05d08b 100644
--- a/internal/ceres/thread_pool_test.cc
+++ b/internal/ceres/thread_pool_test.cc
@@ -28,17 +28,14 @@
 //
 // Author: vitus@google.com (Michael Vitus)
 
-// This include must come before any #ifndef check on Ceres compile options.
-#include "ceres/internal/config.h"
-
-#ifdef CERES_USE_CXX_THREADS
+#include "ceres/thread_pool.h"
 
 #include <chrono>
 #include <condition_variable>
 #include <mutex>
 #include <thread>
 
-#include "ceres/thread_pool.h"
+#include "ceres/internal/config.h"
 #include "glog/logging.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
@@ -193,5 +190,3 @@ TEST(ThreadPool, Resize) {
 }
 
 }  // namespace ceres::internal
-
-#endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/thread_token_provider.cc b/internal/ceres/thread_token_provider.cc
index e48964c95..c9bb3fc00 100644
--- a/internal/ceres/thread_token_provider.cc
+++ b/internal/ceres/thread_token_provider.cc
@@ -30,42 +30,20 @@
 
 #include "ceres/thread_token_provider.h"
 
-#ifdef CERES_USE_OPENMP
-#include <omp.h>
-#endif
-
 namespace ceres::internal {
 
 ThreadTokenProvider::ThreadTokenProvider(int num_threads) {
-  (void)num_threads;
-#ifdef CERES_USE_CXX_THREADS
   for (int i = 0; i < num_threads; i++) {
     pool_.Push(i);
   }
-#endif
 }
 
 int ThreadTokenProvider::Acquire() {
-#ifdef CERES_USE_OPENMP
-  return omp_get_thread_num();
-#endif
-
-#ifdef CERES_NO_THREADS
-  return 0;
-#endif
-
-#ifdef CERES_USE_CXX_THREADS
   int thread_id;
   CHECK(pool_.Wait(&thread_id));
   return thread_id;
-#endif
 }
 
-void ThreadTokenProvider::Release(int thread_id) {
-  (void)thread_id;
-#ifdef CERES_USE_CXX_THREADS
-  pool_.Push(thread_id);
-#endif
-}
+void ThreadTokenProvider::Release(int thread_id) { pool_.Push(thread_id); }
 
 }  // namespace ceres::internal
diff --git a/internal/ceres/thread_token_provider.h b/internal/ceres/thread_token_provider.h
index d8640df2d..b14df0e92 100644
--- a/internal/ceres/thread_token_provider.h
+++ b/internal/ceres/thread_token_provider.h
@@ -31,13 +31,10 @@
 #ifndef CERES_INTERNAL_THREAD_TOKEN_PROVIDER_H_
 #define CERES_INTERNAL_THREAD_TOKEN_PROVIDER_H_
 
+#include "ceres/concurrent_queue.h"
 #include "ceres/internal/config.h"
 #include "ceres/internal/export.h"
 
-#ifdef CERES_USE_CXX_THREADS
-#include "ceres/concurrent_queue.h"
-#endif
-
 namespace ceres::internal {
 
 // Helper for C++ thread number identification that is similar to
@@ -47,12 +44,6 @@ namespace ceres::internal {
 // 0 to num_threads - 1 that can be acquired to identify the thread in a thread
 // pool.
 //
-// If CERES_NO_THREADS is defined, Acquire() always returns 0 and Release()
-// takes no action.
-//
-// If CERES_USE_OPENMP, omp_get_thread_num() is used to Acquire() with no action
-// in Release()
-//
 //
 // Example usage pseudocode:
 //
@@ -77,15 +68,12 @@ class CERES_NO_EXPORT ThreadTokenProvider {
   void Release(int thread_id);
 
  private:
-#ifdef CERES_USE_CXX_THREADS
   // This queue initially holds a sequence from 0..num_threads-1. Every
   // Acquire() call the first number is removed from here. When the token is not
   // needed anymore it shall be given back with corresponding Release()
   // call. This concurrent queue is more expensive than TBB's version, so you
   // should not acquire the thread ID on every for loop iteration.
   ConcurrentQueue<int> pool_;
-#endif
-
   ThreadTokenProvider(ThreadTokenProvider&) = delete;
   ThreadTokenProvider& operator=(ThreadTokenProvider&) = delete;
 };
diff --git a/internal/ceres/wall_time.cc b/internal/ceres/wall_time.cc
index c36092a8e..f57da318c 100644
--- a/internal/ceres/wall_time.cc
+++ b/internal/ceres/wall_time.cc
@@ -30,13 +30,9 @@
 
 #include "ceres/wall_time.h"
 
-#include "ceres/internal/config.h"
-
-#ifdef CERES_USE_OPENMP
-#include <omp.h>
-#else
 #include <ctime>
-#endif
+
+#include "ceres/internal/config.h"
 
 #ifdef _WIN32
 #include <windows.h>
@@ -47,9 +43,6 @@
 namespace ceres::internal {
 
 double WallTimeInSeconds() {
-#ifdef CERES_USE_OPENMP
-  return omp_get_wtime();
-#else
 #ifdef _WIN32
   LARGE_INTEGER count;
   LARGE_INTEGER frequency;
@@ -62,7 +55,6 @@ double WallTimeInSeconds() {
   gettimeofday(&time_val, nullptr);
   return (time_val.tv_sec + time_val.tv_usec * 1e-6);
 #endif
-#endif
 }
 
 EventLogger::EventLogger(const std::string& logger_name) {