diff --git a/sycl/include/sycl/accessor.hpp b/sycl/include/sycl/accessor.hpp
index 288cd82f9104f..672cb83d872e5 100644
--- a/sycl/include/sycl/accessor.hpp
+++ b/sycl/include/sycl/accessor.hpp
@@ -212,16 +212,10 @@
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 class stream;
-namespace ext {
-namespace intel {
-namespace esimd {
-namespace detail {
+namespace ext::intel::esimd::detail {
 // Forward declare a "back-door" access class to support ESIMD.
 class AccessorPrivateProxy;
-} // namespace detail
-} // namespace esimd
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::esimd::detail
 
 template <typename DataT, int Dimensions = 1,
           access::mode AccessMode = access::mode::read_write,
diff --git a/sycl/include/sycl/aliases.hpp b/sycl/include/sycl/aliases.hpp
index 327c9ba808cb5..3205d87c907da 100644
--- a/sycl/include/sycl/aliases.hpp
+++ b/sycl/include/sycl/aliases.hpp
@@ -17,11 +17,9 @@
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 template <typename T, int N> class vec;
-namespace detail {
-namespace half_impl {
+namespace detail::half_impl {
 class half;
-} // namespace half_impl
-} // namespace detail
+} // namespace detail::half_impl
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 
diff --git a/sycl/include/sycl/buffer.hpp b/sycl/include/sycl/buffer.hpp
index 868af8a4b7d7f..f968f40ac7a6f 100644
--- a/sycl/include/sycl/buffer.hpp
+++ b/sycl/include/sycl/buffer.hpp
@@ -36,11 +36,9 @@ class host_accessor;
 template <typename T, int Dimensions, typename AllocatorT, typename Enable>
 class buffer;
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 template <typename SYCLObjT> class weak_object;
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 namespace detail {
 
diff --git a/sycl/include/sycl/builtins.hpp b/sycl/include/sycl/builtins.hpp
index 8f5a565005983..79eae8a82a0ca 100644
--- a/sycl/include/sycl/builtins.hpp
+++ b/sycl/include/sycl/builtins.hpp
@@ -889,16 +889,14 @@ std::enable_if_t<detail::is_geninteger<T>::value, T> ctz(T x) __NOEXC {
 }
 
 // geninteger ctz (geninteger x) for calls with deprecated namespace
-namespace ext {
-namespace intel {
+namespace ext::intel {
 template <typename T>
 __SYCL_DEPRECATED(
     "'sycl::ext::intel::ctz' is deprecated, use 'sycl::ctz' instead")
 std::enable_if_t<sycl::detail::is_geninteger<T>::value, T> ctz(T x) __NOEXC {
   return sycl::ctz(x);
 }
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 
 namespace __SYCL2020_DEPRECATED("use 'ext::intel' instead") intel {
 using namespace ext::intel;
diff --git a/sycl/include/sycl/detail/generic_type_lists.hpp b/sycl/include/sycl/detail/generic_type_lists.hpp
index 95bf664f3d87e..0238d273c0999 100644
--- a/sycl/include/sycl/detail/generic_type_lists.hpp
+++ b/sycl/include/sycl/detail/generic_type_lists.hpp
@@ -22,11 +22,9 @@ namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 template <typename T, int N> class vec;
 template <typename Type, std::size_t NumElements> class marray;
-namespace detail {
-namespace half_impl {
+namespace detail::half_impl {
 class half;
-}
-} // namespace detail
+} // namespace detail::half_impl
 using half = detail::half_impl::half;
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/detail/type_traits.hpp b/sycl/include/sycl/detail/type_traits.hpp
index dde4c0c0b743d..1806882ae8637 100644
--- a/sycl/include/sycl/detail/type_traits.hpp
+++ b/sycl/include/sycl/detail/type_traits.hpp
@@ -20,8 +20,7 @@
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 template <int Dimensions> class group;
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 struct sub_group;
 
 namespace experimental {
@@ -35,8 +34,7 @@ struct is_group_helper<group_with_scratchpad<Group, Extent>> : std::true_type {
 };
 } // namespace detail
 } // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 namespace detail {
 
diff --git a/sycl/include/sycl/detail/usm_impl.hpp b/sycl/include/sycl/detail/usm_impl.hpp
index 5a737cce2b4dd..2eb39ba77575d 100644
--- a/sycl/include/sycl/detail/usm_impl.hpp
+++ b/sycl/include/sycl/detail/usm_impl.hpp
@@ -13,8 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace detail {
-namespace usm {
+namespace detail::usm {
 
 __SYCL_EXPORT void *alignedAlloc(size_t Alignment, size_t Bytes,
                                  const context &Ctxt, const device &Dev,
@@ -28,7 +27,6 @@ __SYCL_EXPORT void *alignedAllocHost(size_t Alignment, size_t Bytes,
 __SYCL_EXPORT void free(void *Ptr, const context &Ctxt,
                         const code_location &CL);
 
-} // namespace usm
-} // namespace detail
+} // namespace detail::usm
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/device.hpp b/sycl/include/sycl/device.hpp
index cd61c722fbe93..e569714133a7c 100644
--- a/sycl/include/sycl/device.hpp
+++ b/sycl/include/sycl/device.hpp
@@ -35,12 +35,10 @@ class device_impl;
 auto getDeviceComparisonLambda();
 } // namespace detail
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 // Forward declaration
 class filter_selector;
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 /// The SYCL device class encapsulates a single SYCL device on which kernels
 /// may be executed.
diff --git a/sycl/include/sycl/device_selector.hpp b/sycl/include/sycl/device_selector.hpp
index 3a890bf5d0ef4..a3add35c3d415 100644
--- a/sycl/include/sycl/device_selector.hpp
+++ b/sycl/include/sycl/device_selector.hpp
@@ -21,11 +21,9 @@ __SYCL_INLINE_VER_NAMESPACE(_V1) {
 // Forward declarations
 class device;
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 class filter_selector;
-}
-} // namespace ext
+} // namespace ext::oneapi
 
 /// The SYCL 1.2.1 device_selector class provides ability to choose the
 /// best SYCL device based on heuristics specified by the user.
diff --git a/sycl/include/sycl/ext/codeplay/experimental/fusion_properties.hpp b/sycl/include/sycl/ext/codeplay/experimental/fusion_properties.hpp
index 5d820456f6e19..5ec2aef927a45 100644
--- a/sycl/include/sycl/ext/codeplay/experimental/fusion_properties.hpp
+++ b/sycl/include/sycl/ext/codeplay/experimental/fusion_properties.hpp
@@ -14,10 +14,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace codeplay {
-namespace experimental {
-namespace property {
+namespace ext::codeplay::experimental::property {
 
 class promote_private
     : public detail::DataLessProperty<detail::FusionPromotePrivate> {};
@@ -33,10 +30,7 @@ namespace queue {
 class enable_fusion : public detail::DataLessProperty<detail::FusionEnable> {};
 } // namespace queue
 
-} // namespace property
-} // namespace experimental
-} // namespace codeplay
-} // namespace ext
+} // namespace ext::codeplay::experimental::property
 
 // Forward declarations
 template <typename T, int Dimensions, typename AllocatorT, typename Enable>
diff --git a/sycl/include/sycl/ext/codeplay/experimental/fusion_wrapper.hpp b/sycl/include/sycl/ext/codeplay/experimental/fusion_wrapper.hpp
index c9fa33810da55..368aea65ed9fa 100644
--- a/sycl/include/sycl/ext/codeplay/experimental/fusion_wrapper.hpp
+++ b/sycl/include/sycl/ext/codeplay/experimental/fusion_wrapper.hpp
@@ -17,9 +17,7 @@ namespace detail {
 class fusion_wrapper_impl;
 }
 
-namespace ext {
-namespace codeplay {
-namespace experimental {
+namespace ext::codeplay::experimental {
 
 ///
 /// A wrapper wrapping a sycl::queue to provide access to the kernel fusion API,
@@ -91,8 +89,6 @@ class __SYCL_EXPORT fusion_wrapper {
 private:
   std::shared_ptr<detail::fusion_wrapper_impl> MImpl;
 };
-} // namespace experimental
-} // namespace codeplay
-} // namespace ext
+} // namespace ext::codeplay::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/esimd/detail/host_util.hpp b/sycl/include/sycl/ext/intel/esimd/detail/host_util.hpp
index cda0b020e6c56..d6123d5d2db36 100644
--- a/sycl/include/sycl/ext/intel/esimd/detail/host_util.hpp
+++ b/sycl/include/sycl/ext/intel/esimd/detail/host_util.hpp
@@ -23,11 +23,9 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace detail {
-namespace half_impl {
+namespace detail::half_impl {
 class half;
-} // namespace half_impl
-} // namespace detail
+} // namespace detail::half_impl
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 
diff --git a/sycl/include/sycl/ext/intel/esimd/detail/region.hpp b/sycl/include/sycl/ext/intel/esimd/detail/region.hpp
index a158ec7ac611d..2cf6edb9f65e0 100644
--- a/sycl/include/sycl/ext/intel/esimd/detail/region.hpp
+++ b/sycl/include/sycl/ext/intel/esimd/detail/region.hpp
@@ -19,9 +19,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace esimd {
+namespace ext::intel::esimd {
 
 /// @cond ESIMD_DETAIL
 // TODO move to detail?
@@ -135,9 +133,7 @@ template <typename T, typename U> T getBaseRegion(std::pair<T, U> Reg) {
 
 /// @endcond ESIMD_DETAIL
 
-} // namespace esimd
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::esimd
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 
diff --git a/sycl/include/sycl/ext/intel/esimd/detail/sycl_util.hpp b/sycl/include/sycl/ext/intel/esimd/detail/sycl_util.hpp
index 51acefad05173..ad607c24e927e 100644
--- a/sycl/include/sycl/ext/intel/esimd/detail/sycl_util.hpp
+++ b/sycl/include/sycl/ext/intel/esimd/detail/sycl_util.hpp
@@ -17,10 +17,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace esimd {
-namespace detail {
+namespace ext::intel::esimd::detail {
 
 // Checks that given type is a SYCL accessor type. Sets its static field
 // \c value accordingly. Also, if the check is succesful, sets \c mode and
@@ -82,10 +79,7 @@ template <typename T, accessor_mode_cap_val_t Capability,
 using EnableIfAccessor = std::enable_if_t<
     detail::is_sycl_accessor_with<T, Capability, AccessTarget>::value, RetT>;
 
-} // namespace detail
-} // namespace esimd
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::esimd::detail
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 
diff --git a/sycl/include/sycl/ext/intel/esimd/native/common.hpp b/sycl/include/sycl/ext/intel/esimd/native/common.hpp
index dab20a27515ec..0df73949a40b2 100644
--- a/sycl/include/sycl/ext/intel/esimd/native/common.hpp
+++ b/sycl/include/sycl/ext/intel/esimd/native/common.hpp
@@ -16,9 +16,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext::intel::esimd {
-namespace native {
-namespace lsc {
+namespace ext::intel::esimd::native::lsc {
 
 /// @addtogroup sycl_esimd_memory
 /// @{
@@ -62,8 +60,6 @@ enum class atomic_op : uint8_t {
 
 /// @} sycl_esimd_memory_lsc
 
-} // namespace lsc
-} // namespace native
-} // namespace ext::intel::esimd
+} // namespace ext::intel::esimd::native::lsc
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/experimental/esimd/memory.hpp b/sycl/include/sycl/ext/intel/experimental/esimd/memory.hpp
index 880fa2ceb7e7a..705eba5818f11 100644
--- a/sycl/include/sycl/ext/intel/experimental/esimd/memory.hpp
+++ b/sycl/include/sycl/ext/intel/experimental/esimd/memory.hpp
@@ -17,10 +17,8 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace experimental {
-namespace esimd {
+namespace ext::intel {
+namespace experimental::esimd {
 
 /// @addtogroup sycl_esimd_memory
 /// @{
@@ -1723,8 +1721,7 @@ __ESIMD_API void lsc_fence(__ESIMD_NS::simd_mask<N> pred = 1) {
 
 /// @} sycl_esimd_memory_lsc
 
-} // namespace esimd
-} // namespace experimental
+} // namespace experimental::esimd
 
 namespace esimd {
 
@@ -1759,7 +1756,6 @@ __ESIMD_API simd<T, N> atomic_update(T *p, simd<unsigned, N> offset,
 }
 
 } // namespace esimd
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/experimental/fpga_lsu.hpp b/sycl/include/sycl/ext/intel/experimental/fpga_lsu.hpp
index 6701dfedb9d41..275157cea5b4b 100644
--- a/sycl/include/sycl/ext/intel/experimental/fpga_lsu.hpp
+++ b/sycl/include/sycl/ext/intel/experimental/fpga_lsu.hpp
@@ -14,9 +14,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace experimental {
+namespace ext::intel::experimental {
 
 constexpr uint8_t BURST_COALESCE = 0x1;
 constexpr uint8_t CACHE = 0x2;
@@ -201,8 +199,6 @@ template <class... _mem_access_params> class lsu final {
 #endif
 };
 
-} // namespace experimental
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/experimental/online_compiler.hpp b/sycl/include/sycl/ext/intel/experimental/online_compiler.hpp
index 8c118250c826c..7767dbdce941e 100644
--- a/sycl/include/sycl/ext/intel/experimental/online_compiler.hpp
+++ b/sycl/include/sycl/ext/intel/experimental/online_compiler.hpp
@@ -17,9 +17,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace experimental {
+namespace ext::intel::experimental {
 
 using byte = unsigned char;
 
@@ -222,8 +220,6 @@ online_compiler<source_language::cm>::compile(const std::string &src) {
   return compile(src, std::vector<std::string>{});
 }
 
-} // namespace experimental
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/experimental/pipes.hpp b/sycl/include/sycl/ext/intel/experimental/pipes.hpp
index 7c3db4d0777b7..b327e1fdd167d 100644
--- a/sycl/include/sycl/ext/intel/experimental/pipes.hpp
+++ b/sycl/include/sycl/ext/intel/experimental/pipes.hpp
@@ -17,9 +17,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace experimental {
+namespace ext::intel::experimental {
 
 template <class _name, class _dataT, int32_t _min_capacity = 0,
           class _propertiesT = decltype(oneapi::experimental::properties{}),
@@ -278,8 +276,6 @@ class pipe<_name, _dataT, _min_capacity, _propertiesT,
 #endif // __SYCL_DEVICE_ONLY__
 };
 
-} // namespace experimental
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/experimental/usm_properties.hpp b/sycl/include/sycl/ext/intel/experimental/usm_properties.hpp
index 4660285767c6c..bd68327e055c0 100644
--- a/sycl/include/sycl/ext/intel/experimental/usm_properties.hpp
+++ b/sycl/include/sycl/ext/intel/experimental/usm_properties.hpp
@@ -8,22 +8,15 @@ namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 namespace ext {
 
-namespace oneapi {
-namespace property {
-namespace usm {
+namespace oneapi::property::usm {
 class device_read_only
     : public sycl::detail::DataLessProperty<sycl::detail::DeviceReadOnly> {
 public:
   device_read_only() = default;
 };
-} // namespace usm
-} // namespace property
-} // namespace oneapi
+} // namespace oneapi::property::usm
 
-namespace intel {
-namespace experimental {
-namespace property {
-namespace usm {
+namespace intel::experimental::property::usm {
 
 class buffer_location
     : public sycl::detail::PropertyWithData<
@@ -36,10 +29,7 @@ class buffer_location
   uint64_t MLocation;
 };
 
-} // namespace usm
-} // namespace property
-} // namespace experimental
-} // namespace intel
+} // namespace intel::experimental::property::usm
 } // namespace ext
 
 template <>
diff --git a/sycl/include/sycl/ext/intel/fpga_device_selector.hpp b/sycl/include/sycl/ext/intel/fpga_device_selector.hpp
index b2170e4f6f25b..8cf3e920045c3 100644
--- a/sycl/include/sycl/ext/intel/fpga_device_selector.hpp
+++ b/sycl/include/sycl/ext/intel/fpga_device_selector.hpp
@@ -20,8 +20,7 @@ __SYCL_INLINE_VER_NAMESPACE(_V1) {
 // Forward declaration
 class platform;
 
-namespace ext {
-namespace intel {
+namespace ext::intel {
 
 namespace detail {
 // Scores a device by platform name.
@@ -102,8 +101,7 @@ class __SYCL2020_DEPRECATED(
   }
 };
 
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/fpga_lsu.hpp b/sycl/include/sycl/ext/intel/fpga_lsu.hpp
index f5428d57bfe48..da331ce51cb1f 100644
--- a/sycl/include/sycl/ext/intel/fpga_lsu.hpp
+++ b/sycl/include/sycl/ext/intel/fpga_lsu.hpp
@@ -13,8 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
+namespace ext::intel {
 constexpr uint8_t BURST_COALESCE = 0x1;
 constexpr uint8_t CACHE = 0x2;
 constexpr uint8_t STATICALLY_COALESCE = 0x4;
@@ -124,8 +123,7 @@ template <class... _mem_access_params> class lsu final {
                   "unable to implement a store LSU with a prefetcher.");
   }
 };
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/fpga_reg.hpp b/sycl/include/sycl/ext/intel/fpga_reg.hpp
index 2c527c8f5ec36..b9f486c347689 100644
--- a/sycl/include/sycl/ext/intel/fpga_reg.hpp
+++ b/sycl/include/sycl/ext/intel/fpga_reg.hpp
@@ -13,8 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
+namespace ext::intel {
 
 // Returns a registered copy of the input
 // This function is intended for FPGA users to instruct the compiler to insert
@@ -43,8 +42,7 @@ fpga_reg(_T t) {
 #endif
 }
 
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/fpga_utils.hpp b/sycl/include/sycl/ext/intel/fpga_utils.hpp
index 289f9edbc7d79..a6954fac357ba 100644
--- a/sycl/include/sycl/ext/intel/fpga_utils.hpp
+++ b/sycl/include/sycl/ext/intel/fpga_utils.hpp
@@ -14,8 +14,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
+namespace ext::intel {
 
 template <template <int32_t> class _Type, class _T>
 struct _MatchType : std::is_same<_Type<_T::value>, _T> {};
@@ -30,8 +29,7 @@ struct _GetValue<_Type, _T1, _T...> {
       std::conditional_t<_MatchType<_Type, _T1>::value, _T1,
                          _GetValue<_Type, _T...>>::value;
 };
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/math.hpp b/sycl/include/sycl/ext/intel/math.hpp
index e58e41f86b4ac..965f9334c5779 100644
--- a/sycl/include/sycl/ext/intel/math.hpp
+++ b/sycl/include/sycl/ext/intel/math.hpp
@@ -49,9 +49,7 @@ _iml_half_internal __imf_truncf16(_iml_half_internal);
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace math {
+namespace ext::intel::math {
 
 static_assert(sizeof(sycl::half) == sizeof(_iml_half_internal),
               "sycl::half is not compatible with _iml_half_internal.");
@@ -198,8 +196,6 @@ std::enable_if_t<std::is_same_v<Tp, sycl::half>, sycl::half> trunc(Tp x) {
 sycl::half2 trunc(sycl::half2 x) {
   return sycl::half2{trunc(x.s0()), trunc(x.s1())};
 }
-} // namespace math
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::math
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/math/imf_half_trivial.hpp b/sycl/include/sycl/ext/intel/math/imf_half_trivial.hpp
index c91f8edd41063..24b925a8ac28c 100644
--- a/sycl/include/sycl/ext/intel/math/imf_half_trivial.hpp
+++ b/sycl/include/sycl/ext/intel/math/imf_half_trivial.hpp
@@ -13,9 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace math {
+namespace ext::intel::math {
 sycl::half hadd(sycl::half x, sycl::half y) { return x + y; }
 
 sycl::half hadd_sat(sycl::half x, sycl::half y) {
@@ -312,8 +310,6 @@ sycl::half2 hfma2_relu(sycl::half2 x, sycl::half2 y, sycl::half2 z) {
 sycl::half habs(sycl::half x) { return sycl::fabs(x); }
 
 sycl::half2 habs2(sycl::half2 x) { return sycl::fabs(x); }
-} // namespace math
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::math
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/intel/pipes.hpp b/sycl/include/sycl/ext/intel/pipes.hpp
index 467198348931b..61a9e742e5cb1 100644
--- a/sycl/include/sycl/ext/intel/pipes.hpp
+++ b/sycl/include/sycl/ext/intel/pipes.hpp
@@ -14,8 +14,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
+namespace ext::intel {
 
 template <class _name, class _dataT, int32_t _min_capacity = 0> class pipe {
 public:
@@ -218,8 +217,7 @@ class kernel_writeable_io_pipe {
 #endif // __SYCL_DEVICE_ONLY__
 };
 
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/accessor_property_list.hpp b/sycl/include/sycl/ext/oneapi/accessor_property_list.hpp
index 8dbef4d4c15f7..7083b26f4252f 100644
--- a/sycl/include/sycl/ext/oneapi/accessor_property_list.hpp
+++ b/sycl/include/sycl/ext/oneapi/accessor_property_list.hpp
@@ -25,8 +25,7 @@ namespace detail {
 // of each compile-time-constant property.
 template <typename T> struct IsCompileTimePropertyInstance : std::false_type {};
 } // namespace detail
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 template <typename T> struct is_compile_time_property : std::false_type {};
 
@@ -227,8 +226,7 @@ class __SYCL_TYPE(accessor_property_list) accessor_property_list
                                   PropsT...>::value;
   }
 };
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/atomic_accessor.hpp b/sycl/include/sycl/ext/oneapi/atomic_accessor.hpp
index a16c18eb119e3..c6318468a041a 100644
--- a/sycl/include/sycl/ext/oneapi/atomic_accessor.hpp
+++ b/sycl/include/sycl/ext/oneapi/atomic_accessor.hpp
@@ -15,8 +15,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 template <memory_order> struct order_tag_t {
   explicit order_tag_t() = default;
@@ -114,8 +113,6 @@ atomic_accessor(buffer<DataT, Dimensions, AllocatorT>, handler,
                 order_tag_t<Order>, scope_tag_t<Scope>, property_list = {})
     -> atomic_accessor<DataT, Dimensions, Order, Scope, target::device,
                        access::placeholder::false_t>;
-} // namespace oneapi
-} // namespace ext
-
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/atomic_enums.hpp b/sycl/include/sycl/ext/oneapi/atomic_enums.hpp
index 5bb84647b7de6..f6451112ec10e 100644
--- a/sycl/include/sycl/ext/oneapi/atomic_enums.hpp
+++ b/sycl/include/sycl/ext/oneapi/atomic_enums.hpp
@@ -21,8 +21,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 using memory_order __SYCL2020_DEPRECATED("use 'sycl::memory_order' instead") =
     sycl::memory_order;
@@ -76,7 +75,6 @@ getStdMemoryOrder(::sycl::ext::oneapi::memory_order order) {
 } // namespace detail
 #endif // __SYCL_DEVICE_ONLY__
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/atomic_fence.hpp b/sycl/include/sycl/ext/oneapi/atomic_fence.hpp
index 7caf4d8ab8201..fa9038c171d29 100644
--- a/sycl/include/sycl/ext/oneapi/atomic_fence.hpp
+++ b/sycl/include/sycl/ext/oneapi/atomic_fence.hpp
@@ -18,8 +18,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 namespace detail {
 using namespace sycl::detail;
 }
@@ -37,8 +36,7 @@ static inline void atomic_fence(memory_order order, memory_scope scope) {
 #endif
 }
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/atomic_ref.hpp b/sycl/include/sycl/ext/oneapi/atomic_ref.hpp
index a470c8db10ffc..5b181aed58d0a 100644
--- a/sycl/include/sycl/ext/oneapi/atomic_ref.hpp
+++ b/sycl/include/sycl/ext/oneapi/atomic_ref.hpp
@@ -23,8 +23,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 namespace detail {
 
 // Import from detail:: into ext::oneapi::detail:: to improve readability later
@@ -668,8 +667,7 @@ class __SYCL2020_DEPRECATED("use 'sycl::atomic_ref' instead") atomic_ref
                                 AddressSpace>::operator=;
 };
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/backend/level_zero.hpp b/sycl/include/sycl/ext/oneapi/backend/level_zero.hpp
index f1b15ec866159..82f4fc31f68c1 100644
--- a/sycl/include/sycl/ext/oneapi/backend/level_zero.hpp
+++ b/sycl/include/sycl/ext/oneapi/backend/level_zero.hpp
@@ -14,9 +14,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace level_zero {
+namespace ext::oneapi::level_zero {
 // Implementation of various "make" functions resides in libsycl.so and thus
 // their interface needs to be backend agnostic.
 // TODO: remove/merge with similar functions in sycl::detail
@@ -100,9 +98,7 @@ T make(const context &Context,
   return make_event(Context, reinterpret_cast<pi_native_handle>(Interop),
                     Ownership == ownership::keep);
 }
-} // namespace level_zero
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::level_zero
 
 // Specialization of sycl::make_context for Level-Zero backend.
 template <>
diff --git a/sycl/include/sycl/ext/oneapi/backend/level_zero_ownership.hpp b/sycl/include/sycl/ext/oneapi/backend/level_zero_ownership.hpp
index 192ac71fc72b7..d892211770cc4 100644
--- a/sycl/include/sycl/ext/oneapi/backend/level_zero_ownership.hpp
+++ b/sycl/include/sycl/ext/oneapi/backend/level_zero_ownership.hpp
@@ -12,9 +12,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace level_zero {
+namespace ext::oneapi::level_zero {
 
 // Since Level-Zero is not doing any reference counting itself, we have to
 // be explicit about the ownership of the native handles used in the
@@ -22,8 +20,6 @@ namespace level_zero {
 //
 enum class ownership { transfer, keep };
 
-} // namespace level_zero
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::level_zero
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/bf16_storage_builtins.hpp b/sycl/include/sycl/ext/oneapi/bf16_storage_builtins.hpp
index 834c10ba5e043..b38637dc2415d 100644
--- a/sycl/include/sycl/ext/oneapi/bf16_storage_builtins.hpp
+++ b/sycl/include/sycl/ext/oneapi/bf16_storage_builtins.hpp
@@ -9,8 +9,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 namespace detail {
 
@@ -81,7 +80,6 @@ std::enable_if_t<detail::is_bf16_storage_type<T>::value, T> fma(T x, T y, T z) {
 #endif
 }
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/bfloat16.hpp b/sycl/include/sycl/ext/oneapi/bfloat16.hpp
index 203ca0b9b9a3c..06c1d8a966277 100644
--- a/sycl/include/sycl/ext/oneapi/bfloat16.hpp
+++ b/sycl/include/sycl/ext/oneapi/bfloat16.hpp
@@ -22,8 +22,7 @@ __devicelib_ConvertBF16ToFINTEL(const uint16_t &) noexcept;
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 class bfloat16;
 
@@ -226,8 +225,7 @@ inline bfloat16 bitsToBfloat16(const Bfloat16StorageT Value) {
 
 } // namespace detail
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/device_global/device_global.hpp b/sycl/include/sycl/ext/oneapi/device_global/device_global.hpp
index 48d6126888d3c..ab89a88c7481b 100644
--- a/sycl/include/sycl/ext/oneapi/device_global/device_global.hpp
+++ b/sycl/include/sycl/ext/oneapi/device_global/device_global.hpp
@@ -27,9 +27,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 namespace detail {
 // Type-trait for checking if a type defines `operator->`.
@@ -200,9 +198,7 @@ class
   }
 };
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 
diff --git a/sycl/include/sycl/ext/oneapi/device_global/properties.hpp b/sycl/include/sycl/ext/oneapi/device_global/properties.hpp
index b7527e3628909..da627043807c8 100644
--- a/sycl/include/sycl/ext/oneapi/device_global/properties.hpp
+++ b/sycl/include/sycl/ext/oneapi/device_global/properties.hpp
@@ -13,9 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 template <typename T, typename PropertyListT> class device_global;
 
@@ -131,8 +129,6 @@ struct PropertyMetaInfo<implement_in_csr_key::value_t<Enable>> {
 };
 
 } // namespace detail
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/dot_product.hpp b/sycl/include/sycl/ext/oneapi/dot_product.hpp
old mode 100755
new mode 100644
index adae8f6139cc7..7d2ef8582a151
--- a/sycl/include/sycl/ext/oneapi/dot_product.hpp
+++ b/sycl/include/sycl/ext/oneapi/dot_product.hpp
@@ -15,8 +15,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 union Us {
   char s[4];
@@ -75,8 +74,7 @@ int32_t dot_acc(vec<int8_t, 4> a, vec<uint8_t, 4> b, int32_t c) {
          c;
 }
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/experimental/backend/cuda.hpp b/sycl/include/sycl/ext/oneapi/experimental/backend/cuda.hpp
index a600bf8f6165a..1850b76aaf4df 100644
--- a/sycl/include/sycl/ext/oneapi/experimental/backend/cuda.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/backend/cuda.hpp
@@ -16,9 +16,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace cuda {
+namespace ext::oneapi::cuda {
 
 // Implementation of ext_oneapi_cuda::make<device>
 inline __SYCL_EXPORT device make_device(pi_native_handle NativeHandle) {
@@ -33,9 +31,7 @@ inline __SYCL_EXPORT bool has_native_event(event sycl_event) {
   return false;
 }
 
-} // namespace cuda
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::cuda
 
 // CUDA context specialization
 template <>
diff --git a/sycl/include/sycl/ext/oneapi/experimental/bfloat16_math.hpp b/sycl/include/sycl/ext/oneapi/experimental/bfloat16_math.hpp
index f6d0039780153..26d3d3bdc7ec3 100644
--- a/sycl/include/sycl/ext/oneapi/experimental/bfloat16_math.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/bfloat16_math.hpp
@@ -19,9 +19,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 namespace detail {
 template <size_t N>
@@ -209,8 +207,6 @@ sycl::marray<bfloat16, N> fma(sycl::marray<bfloat16, N> x,
 #endif // defined(__SYCL_DEVICE_ONLY__) && defined(__NVPTX__)
 }
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/experimental/builtins.hpp b/sycl/include/sycl/ext/oneapi/experimental/builtins.hpp
index 148cbe47115c1..06939fcf509ad 100755
--- a/sycl/include/sycl/ext/oneapi/experimental/builtins.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/builtins.hpp
@@ -28,9 +28,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 // Provides functionality to print data from kernels in a C way:
 // - On non-host devices this function is directly mapped to printf from
@@ -179,9 +177,7 @@ exp2(sycl::marray<half, N> x) __NOEXC {
 
 } // namespace native
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 
diff --git a/sycl/include/sycl/ext/oneapi/experimental/group_helpers_sorters.hpp b/sycl/include/sycl/ext/oneapi/experimental/group_helpers_sorters.hpp
index dbd50379e6679..d390134f380ee 100644
--- a/sycl/include/sycl/ext/oneapi/experimental/group_helpers_sorters.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/group_helpers_sorters.hpp
@@ -13,9 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 // ---- group helpers
 template <typename Group, std::size_t Extent> class group_with_scratchpad {
@@ -92,9 +90,7 @@ template <typename Compare = std::less<>> class default_sorter {
   }
 };
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 #endif
diff --git a/sycl/include/sycl/ext/oneapi/experimental/group_sort.hpp b/sycl/include/sycl/ext/oneapi/experimental/group_sort.hpp
index e8285c3eb89fa..beea117bbc9d0 100644
--- a/sycl/include/sycl/ext/oneapi/experimental/group_sort.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/group_sort.hpp
@@ -18,9 +18,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 namespace detail {
 
 // ---- traits
@@ -135,9 +133,7 @@ joint_sort(experimental::group_with_scratchpad<Group, Extent> exec, Iter first,
              experimental::default_sorter<>(exec.get_memory()));
 }
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 #endif
diff --git a/sycl/include/sycl/ext/oneapi/experimental/invoke_simd.hpp b/sycl/include/sycl/ext/oneapi/experimental/invoke_simd.hpp
index 5fd676d153d85..69ec803fd232e 100644
--- a/sycl/include/sycl/ext/oneapi/experimental/invoke_simd.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/invoke_simd.hpp
@@ -71,9 +71,7 @@ __builtin_invoke_simd(HelperFunc helper, UserSimdFuncAndSpmdArgs... args)
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 // --- Basic definitions prescribed by the spec.
 namespace simd_abi {
@@ -370,8 +368,6 @@ __attribute__((always_inline)) auto invoke_simd(sycl::sub_group sg,
 #endif // __INVOKE_SIMD_ENABLE_ALL_CALLABLES
 }
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/experimental/spec_constant.hpp b/sycl/include/sycl/ext/oneapi/experimental/spec_constant.hpp
index ff2ededc46383..3e6cfa0a86a4c 100644
--- a/sycl/include/sycl/ext/oneapi/experimental/spec_constant.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/spec_constant.hpp
@@ -22,9 +22,7 @@
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 class spec_const_error : public compile_program_error {
   using compile_program_error::compile_program_error;
@@ -77,9 +75,7 @@ class __SYCL2020_DEPRECATED(
   }
 };
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/experimental/uniform.hpp b/sycl/include/sycl/ext/oneapi/experimental/uniform.hpp
index 44955b2627155..6a7c4dabf207c 100644
--- a/sycl/include/sycl/ext/oneapi/experimental/uniform.hpp
+++ b/sycl/include/sycl/ext/oneapi/experimental/uniform.hpp
@@ -22,13 +22,11 @@
 // Forward declarations of types not allowed to be wrapped in uniform:
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 struct sub_group;
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 template <int, bool> class item;
 template <int> class id;
@@ -43,9 +41,7 @@ using ext::oneapi::sub_group;
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 namespace detail {
 
 template <class T, template <int> class Tmpl>
@@ -115,8 +111,6 @@ template <class T> class uniform {
   T Val;
 };
 
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/filter_selector.hpp b/sycl/include/sycl/ext/oneapi/filter_selector.hpp
index 3f14daac38546..a78c5ae73bc1b 100644
--- a/sycl/include/sycl/ext/oneapi/filter_selector.hpp
+++ b/sycl/include/sycl/ext/oneapi/filter_selector.hpp
@@ -22,8 +22,7 @@ __SYCL_INLINE_VER_NAMESPACE(_V1) {
 class device;
 class device_selector;
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 namespace detail {
 class filter_selector_impl;
 } // namespace detail
@@ -38,8 +37,7 @@ class __SYCL_EXPORT filter_selector : public device_selector {
 private:
   std::shared_ptr<detail::filter_selector_impl> impl;
 };
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 #ifdef __SYCL_INTERNAL_API
 namespace __SYCL2020_DEPRECATED("use 'ext::oneapi' instead") ONEAPI {
diff --git a/sycl/include/sycl/ext/oneapi/functional.hpp b/sycl/include/sycl/ext/oneapi/functional.hpp
index 03b7b28f7621e..16b19eab3c59a 100644
--- a/sycl/include/sycl/ext/oneapi/functional.hpp
+++ b/sycl/include/sycl/ext/oneapi/functional.hpp
@@ -13,8 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 template <typename T = void> using plus = std::plus<T>;
 template <typename T = void> using multiplies = std::multiplies<T>;
@@ -24,8 +23,7 @@ template <typename T = void> using bit_and = std::bit_and<T>;
 template <typename T = void> using maximum = sycl::maximum<T>;
 template <typename T = void> using minimum = sycl::minimum<T>;
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 #ifdef __SYCL_DEVICE_ONLY__
 namespace detail {
diff --git a/sycl/include/sycl/ext/oneapi/group_algorithm.hpp b/sycl/include/sycl/ext/oneapi/group_algorithm.hpp
index 2d163363cfbc0..2500c84065032 100644
--- a/sycl/include/sycl/ext/oneapi/group_algorithm.hpp
+++ b/sycl/include/sycl/ext/oneapi/group_algorithm.hpp
@@ -21,8 +21,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 // EnableIf shorthands for algorithms that depend only on type
 template <typename T>
@@ -540,8 +539,7 @@ std::enable_if_t<detail::is_generic_group<Group>::value, bool> leader(Group g) {
 #endif
 }
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/group_local_memory.hpp b/sycl/include/sycl/ext/oneapi/group_local_memory.hpp
index e8c60a100079e..8aafde131790c 100644
--- a/sycl/include/sycl/ext/oneapi/group_local_memory.hpp
+++ b/sycl/include/sycl/ext/oneapi/group_local_memory.hpp
@@ -21,8 +21,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 template <typename T, typename Group>
 std::enable_if_t<
     std::is_trivially_destructible<T>::value &&
@@ -66,7 +65,6 @@ std::enable_if_t<
       PI_ERROR_INVALID_OPERATION);
 #endif
 }
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/kernel_properties/properties.hpp b/sycl/include/sycl/ext/oneapi/kernel_properties/properties.hpp
index 3a451a1922665..aa1814868491d 100644
--- a/sycl/include/sycl/ext/oneapi/kernel_properties/properties.hpp
+++ b/sycl/include/sycl/ext/oneapi/kernel_properties/properties.hpp
@@ -17,9 +17,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 namespace detail {
 // Trait for checking that all size_t values are non-zero.
 template <size_t... Xs> struct AllNonZero {
@@ -184,9 +182,7 @@ struct HasKernelPropertiesGetMethod<T,
 };
 
 } // namespace detail
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
 
diff --git a/sycl/include/sycl/ext/oneapi/matrix/matrix-jit-use.hpp b/sycl/include/sycl/ext/oneapi/matrix/matrix-jit-use.hpp
index 2a7e1ef3ad060..12ce5653fe193 100644
--- a/sycl/include/sycl/ext/oneapi/matrix/matrix-jit-use.hpp
+++ b/sycl/include/sycl/ext/oneapi/matrix/matrix-jit-use.hpp
@@ -15,10 +15,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
-namespace matrix {
+namespace ext::oneapi::experimental::matrix {
 
 // packed_a and packed_b will be replaced by packed once the use implementation
 // is stable.
@@ -641,9 +638,6 @@ class wi_data {
   }
 };
 
-} // namespace matrix
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental::matrix
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/matrix/matrix-jit.hpp b/sycl/include/sycl/ext/oneapi/matrix/matrix-jit.hpp
index 21884a1bd6f4d..fa5ad5b530e2b 100644
--- a/sycl/include/sycl/ext/oneapi/matrix/matrix-jit.hpp
+++ b/sycl/include/sycl/ext/oneapi/matrix/matrix-jit.hpp
@@ -15,10 +15,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
-namespace matrix {
+namespace ext::oneapi::experimental::matrix {
 
 enum class matrix_layout { row_major, col_major, packed_a, packed_b };
 
@@ -620,9 +617,6 @@ class wi_data {
 
 #undef SPV_MATRIX_LAYOUT_TRAITS
 
-} // namespace matrix
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental::matrix
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/matrix/matrix-tensorcore.hpp b/sycl/include/sycl/ext/oneapi/matrix/matrix-tensorcore.hpp
index 6766b47bd196a..37120646ecad1 100644
--- a/sycl/include/sycl/ext/oneapi/matrix/matrix-tensorcore.hpp
+++ b/sycl/include/sycl/ext/oneapi/matrix/matrix-tensorcore.hpp
@@ -12,10 +12,8 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
-namespace matrix {
+namespace ext::oneapi {
+namespace experimental::matrix {
 
 enum class matrix_use { a, b, accumulator };
 
@@ -173,8 +171,7 @@ joint_matrix_fill(Group sg,
 #endif // defined(__SYCL_DEVICE_ONLY__) && defined(__NVPTX__)
 }
 
-} // namespace matrix
-} // namespace experimental
+} // namespace experimental::matrix
 
 namespace detail {
 
@@ -684,8 +681,7 @@ struct joint_matrix_mad_impl<
 };
 } // namespace detail
 
-namespace experimental {
-namespace matrix {
+namespace experimental::matrix {
 
 template <
     typename Group, typename S, typename T, matrix_use Use, size_t NumRows,
@@ -776,9 +772,7 @@ inline __SYCL_ALWAYS_INLINE float round_to_tf32(float a) {
 #endif // defined(__SYCL_DEVICE_ONLY__) && defined(__NVPTX__)
 }
 
-} // namespace matrix
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace experimental::matrix
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/owner_less.hpp b/sycl/include/sycl/ext/oneapi/owner_less.hpp
index c05554b95a6c8..2c35e7468ba80 100644
--- a/sycl/include/sycl/ext/oneapi/owner_less.hpp
+++ b/sycl/include/sycl/ext/oneapi/owner_less.hpp
@@ -22,8 +22,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 namespace detail {
 template <typename SyclObject> struct owner_less_base {
@@ -95,7 +94,6 @@ template <typename DataT, int Dimensions>
 struct owner_less<local_accessor<DataT, Dimensions>>
     : public detail::owner_less_base<local_accessor<DataT, Dimensions>> {};
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/properties/properties.hpp b/sycl/include/sycl/ext/oneapi/properties/properties.hpp
index 50dcad9d7ae84..f2288e41cd5ad 100644
--- a/sycl/include/sycl/ext/oneapi/properties/properties.hpp
+++ b/sycl/include/sycl/ext/oneapi/properties/properties.hpp
@@ -19,9 +19,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 namespace detail {
 
@@ -223,9 +221,7 @@ using merged_properties_t =
     typename merged_properties<LHSPropertiesT, RHSPropertiesT>::type;
 
 } // namespace detail
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 
 // If property_list is not trivially copyable, allow properties to propagate
 // is_device_copyable
diff --git a/sycl/include/sycl/ext/oneapi/properties/property_utils.hpp b/sycl/include/sycl/ext/oneapi/properties/property_utils.hpp
index b27b9080b9d62..01d5c2f2d4f99 100644
--- a/sycl/include/sycl/ext/oneapi/properties/property_utils.hpp
+++ b/sycl/include/sycl/ext/oneapi/properties/property_utils.hpp
@@ -15,9 +15,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 
 // Forward declaration
 template <typename PropertyT, typename... Ts> struct property_value;
@@ -380,8 +378,6 @@ template <size_t... Sizes>
 struct SizeListToStr : SizeListToStrHelper<SizeList<Sizes...>, CharList<>> {};
 
 } // namespace detail
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/properties/property_value.hpp b/sycl/include/sycl/ext/oneapi/properties/property_value.hpp
index b086f380653bc..9c8996bf76c61 100644
--- a/sycl/include/sycl/ext/oneapi/properties/property_value.hpp
+++ b/sycl/include/sycl/ext/oneapi/properties/property_value.hpp
@@ -13,9 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 namespace detail {
 
 // Base class for property values with a single non-type value
@@ -86,8 +84,6 @@ struct IsCompileTimePropertyValue<property_value<PropertyT, PropertyValueTs...>>
     : IsCompileTimeProperty<PropertyT> {};
 
 } // namespace detail
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/sub_group.hpp b/sycl/include/sycl/ext/oneapi/sub_group.hpp
index b85567ef2347f..0c9627f47c470 100644
--- a/sycl/include/sycl/ext/oneapi/sub_group.hpp
+++ b/sycl/include/sycl/ext/oneapi/sub_group.hpp
@@ -121,8 +121,7 @@ GetUnqualMultiPtr(const multi_ptr<CVT, Space, IsDecorated> &Mptr) {
 
 } // namespace detail
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 struct sub_group;
 namespace experimental {
@@ -791,8 +790,7 @@ inline sub_group this_sub_group() {
 #endif
 }
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/sub_group_mask.hpp b/sycl/include/sycl/ext/oneapi/sub_group_mask.hpp
index 6cc45593396a0..2cca058cb60cd 100644
--- a/sycl/include/sycl/ext/oneapi/sub_group_mask.hpp
+++ b/sycl/include/sycl/ext/oneapi/sub_group_mask.hpp
@@ -20,8 +20,7 @@ namespace detail {
 class Builder;
 } // namespace detail
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 #if defined(__SYCL_DEVICE_ONLY__) && defined(__AMDGCN__) &&                    \
     (__AMDGCN_WAVEFRONT_SIZE == 64)
@@ -287,7 +286,6 @@ group_ballot(Group g, bool predicate) {
 
 #undef BITS_TYPE
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/weak_object.hpp b/sycl/include/sycl/ext/oneapi/weak_object.hpp
index 97a192afd6328..33d797e77f57a 100644
--- a/sycl/include/sycl/ext/oneapi/weak_object.hpp
+++ b/sycl/include/sycl/ext/oneapi/weak_object.hpp
@@ -16,8 +16,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 namespace detail {
 // Helper for creating ranges for empty weak_objects.
 template <int Dims> static range<Dims> createDummyRange() {
@@ -128,7 +127,6 @@ class weak_object<buffer<T, Dimensions, AllocatorT>>
   bool MIsSubBuffer;
 };
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/ext/oneapi/weak_object_base.hpp b/sycl/include/sycl/ext/oneapi/weak_object_base.hpp
index f2b448e54bdd1..52877d9d64c9f 100644
--- a/sycl/include/sycl/ext/oneapi/weak_object_base.hpp
+++ b/sycl/include/sycl/ext/oneapi/weak_object_base.hpp
@@ -12,9 +12,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace detail {
+namespace ext::oneapi::detail {
 template <typename SYCLObjT> class weak_object_base;
 
 // Helper function for getting the underlying weak_ptr from a weak_object.
@@ -59,8 +57,6 @@ template <typename SYCLObjT> class weak_object_base {
   friend decltype(weak_object_base<Obj>::MObjWeakPtr)
   detail::getSyclWeakObjImpl(const weak_object_base<Obj> &WeakObj);
 };
-} // namespace detail
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::detail
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/group.hpp b/sycl/include/sycl/group.hpp
index 4097928ba5108..9596b066e0857 100644
--- a/sycl/include/sycl/group.hpp
+++ b/sycl/include/sycl/group.hpp
@@ -549,9 +549,7 @@ group<Dims> this_group() {
 #endif
 }
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 template <int Dims> group<Dims> this_group() {
 #ifdef __SYCL_DEVICE_ONLY__
   return sycl::detail::Builder::getElement(
@@ -562,8 +560,6 @@ template <int Dims> group<Dims> this_group() {
       "Free function calls are not supported on host device");
 #endif
 }
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/half_type.hpp b/sycl/include/sycl/half_type.hpp
index 6f5c3cc2f1e33..ace7be7352c6c 100644
--- a/sycl/include/sycl/half_type.hpp
+++ b/sycl/include/sycl/half_type.hpp
@@ -34,15 +34,9 @@
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 
-namespace ext {
-namespace intel {
-namespace esimd {
-namespace detail {
+namespace ext::intel::esimd::detail {
 class WrapperElementTypeProxy;
-} // namespace detail
-} // namespace esimd
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::esimd::detail
 
 namespace detail {
 
diff --git a/sycl/include/sycl/id.hpp b/sycl/include/sycl/id.hpp
index 24ab8017a13fa..82abc059b4d40 100644
--- a/sycl/include/sycl/id.hpp
+++ b/sycl/include/sycl/id.hpp
@@ -360,9 +360,7 @@ id<Dims> this_id() {
 #endif
 }
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 template <int Dims> id<Dims> this_id() {
 #ifdef __SYCL_DEVICE_ONLY__
   return sycl::detail::Builder::getElement(sycl::detail::declptr<id<Dims>>());
@@ -372,8 +370,6 @@ template <int Dims> id<Dims> this_id() {
       "Free function calls are not supported on host device");
 #endif
 }
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/info/info_desc.hpp b/sycl/include/sycl/info/info_desc.hpp
index 20d6d9b376edb..0e776b3930e4d 100644
--- a/sycl/include/sycl/info/info_desc.hpp
+++ b/sycl/include/sycl/info/info_desc.hpp
@@ -179,17 +179,9 @@ template <typename T, T param> struct compatibility_param_traits {};
   } /*namespace info */                                                        \
   } /*namespace Namespace */
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
-namespace info {
-namespace device {
+namespace ext::oneapi::experimental::info::device {
 template <int Dimensions> struct max_work_groups;
-} // namespace device
-} // namespace info
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental::info::device
 #include <sycl/info/ext_intel_device_traits.def>
 #include <sycl/info/ext_oneapi_device_traits.def>
 #undef __SYCL_PARAM_TRAITS_SPEC
diff --git a/sycl/include/sycl/item.hpp b/sycl/include/sycl/item.hpp
index 2c315031c89b0..74ef41ce0c495 100644
--- a/sycl/include/sycl/item.hpp
+++ b/sycl/include/sycl/item.hpp
@@ -152,9 +152,7 @@ item<Dims> this_item() {
 #endif
 }
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 template <int Dims> item<Dims> this_item() {
 #ifdef __SYCL_DEVICE_ONLY__
   return sycl::detail::Builder::getElement(sycl::detail::declptr<item<Dims>>());
@@ -164,8 +162,6 @@ template <int Dims> item<Dims> this_item() {
       "Free function calls are not supported on host device");
 #endif
 }
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/nd_item.hpp b/sycl/include/sycl/nd_item.hpp
index 9f19e91220ab4..989dd00bbdb10 100644
--- a/sycl/include/sycl/nd_item.hpp
+++ b/sycl/include/sycl/nd_item.hpp
@@ -202,9 +202,7 @@ nd_item<Dims> this_nd_item() {
 #endif
 }
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 template <int Dims> nd_item<Dims> this_nd_item() {
 #ifdef __SYCL_DEVICE_ONLY__
   return sycl::detail::Builder::getElement(
@@ -215,8 +213,6 @@ template <int Dims> nd_item<Dims> this_nd_item() {
       "Free function calls are not supported on host device");
 #endif
 }
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/include/sycl/platform.hpp b/sycl/include/sycl/platform.hpp
index 8bba6c05b8641..fd4534adf880f 100644
--- a/sycl/include/sycl/platform.hpp
+++ b/sycl/include/sycl/platform.hpp
@@ -34,12 +34,10 @@ auto get_native(const SyclObjectT &Obj)
 namespace detail {
 class platform_impl;
 }
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 // Forward declaration
 class filter_selector;
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 /// Encapsulates a SYCL platform on which kernels may be executed.
 ///
diff --git a/sycl/include/sycl/properties/accessor_properties.hpp b/sycl/include/sycl/properties/accessor_properties.hpp
index b320a37dc3759..14d478183e5a8 100644
--- a/sycl/include/sycl/properties/accessor_properties.hpp
+++ b/sycl/include/sycl/properties/accessor_properties.hpp
@@ -30,8 +30,7 @@ inline constexpr property::no_init no_init;
 __SYCL2020_DEPRECATED("spelling is now: no_init")
 inline constexpr property::noinit noinit;
 
-namespace ext {
-namespace intel {
+namespace ext::intel {
 namespace property {
 struct __SYCL_TYPE(buffer_location) buffer_location {
   template <int A = 0> struct instance {
@@ -50,11 +49,9 @@ struct __SYCL_TYPE(buffer_location) buffer_location {
 
 template <int A>
 inline constexpr property::buffer_location::instance<A> buffer_location{};
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 namespace property {
 struct no_offset {
   template <bool B = true> struct instance {
@@ -90,8 +87,7 @@ struct is_compile_time_property<ext::oneapi::property::no_alias>
 template <>
 struct is_compile_time_property<sycl::ext::intel::property::buffer_location>
     : std::true_type {};
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 // Forward declaration
 template <typename DataT, int Dimensions, access::mode AccessMode,
@@ -101,8 +97,7 @@ class accessor;
 template <typename DataT, int Dimensions, access::mode AccessMode>
 class host_accessor;
 
-namespace detail {
-namespace acc_properties {
+namespace detail::acc_properties {
 template <typename T> struct is_accessor : std::false_type {};
 template <typename DataT, int Dimensions, access::mode AccessMode,
           access::target AccessTarget, access::placeholder IsPlaceholder,
@@ -114,8 +109,7 @@ template <typename T> struct is_host_accessor : std::false_type {};
 template <typename DataT, int Dimensions, access::mode AccessMode>
 struct is_host_accessor<host_accessor<DataT, Dimensions, AccessMode>>
     : std::true_type {};
-} // namespace acc_properties
-} // namespace detail
+} // namespace detail::acc_properties
 
 // Accessor property trait specializations
 template <>
diff --git a/sycl/include/sycl/properties/buffer_properties.hpp b/sycl/include/sycl/properties/buffer_properties.hpp
index 07961e17c4d19..472c9697a812a 100644
--- a/sycl/include/sycl/properties/buffer_properties.hpp
+++ b/sycl/include/sycl/properties/buffer_properties.hpp
@@ -15,8 +15,7 @@
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
 
-namespace property {
-namespace buffer {
+namespace property::buffer {
 class use_host_ptr : public detail::DataLessProperty<detail::BufferUseHostPtr> {
 };
 
@@ -63,20 +62,13 @@ class buffer_location
   uint64_t MLocation;
 };
 } // namespace detail
-} // namespace buffer
-} // namespace property
+} // namespace property::buffer
 
-namespace ext {
-namespace oneapi {
-namespace property {
-namespace buffer {
+namespace ext::oneapi::property::buffer {
 
 class use_pinned_host_memory : public sycl::detail::DataLessProperty<
                                    sycl::detail::BufferUsePinnedHostMemory> {};
-} // namespace buffer
-} // namespace property
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::property::buffer
 
 // Forward declaration
 template <typename T, int Dimensions, typename AllocatorT, typename Enable>
diff --git a/sycl/include/sycl/properties/context_properties.hpp b/sycl/include/sycl/properties/context_properties.hpp
index 69ea7da5502da..443448684e001 100644
--- a/sycl/include/sycl/properties/context_properties.hpp
+++ b/sycl/include/sycl/properties/context_properties.hpp
@@ -14,21 +14,12 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace cuda {
-namespace property {
-namespace context {
+namespace ext::oneapi::cuda::property::context {
 class use_primary_context : public ::sycl::detail::DataLessProperty<
                                 ::sycl::detail::UsePrimaryContext> {};
-} // namespace context
-} // namespace property
-} // namespace cuda
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::cuda::property::context
 
-namespace property {
-namespace context {
+namespace property::context {
 namespace __SYCL2020_DEPRECATED(
     "use 'sycl::ext::oneapi::cuda::property::context' instead") cuda {
 class use_primary_context
@@ -37,8 +28,7 @@ class use_primary_context
 // clang-format off
 } // namespace cuda
 // clang-format on
-} // namespace context
-} // namespace property
+} // namespace property::context
 
 // Forward declaration
 class context;
diff --git a/sycl/include/sycl/properties/image_properties.hpp b/sycl/include/sycl/properties/image_properties.hpp
index 9c4bdf2162b21..a5b942fff6566 100644
--- a/sycl/include/sycl/properties/image_properties.hpp
+++ b/sycl/include/sycl/properties/image_properties.hpp
@@ -14,8 +14,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace property {
-namespace image {
+namespace property::image {
 class use_host_ptr : public detail::DataLessProperty<detail::ImageUseHostPtr> {
 };
 
@@ -39,8 +38,7 @@ class context_bound
 private:
   sycl::context MCtx;
 };
-} // namespace image
-} // namespace property
+} // namespace property::image
 
 // Forward declaration
 template <int Dimensions, typename AllocatorT> class image;
diff --git a/sycl/include/sycl/properties/queue_properties.hpp b/sycl/include/sycl/properties/queue_properties.hpp
index d44bc85bda85c..d0865d1e16f42 100644
--- a/sycl/include/sycl/properties/queue_properties.hpp
+++ b/sycl/include/sycl/properties/queue_properties.hpp
@@ -13,19 +13,15 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace property {
-namespace queue {
+namespace property::queue {
 class in_order : public detail::DataLessProperty<detail::InOrder> {};
 class enable_profiling
     : public detail::DataLessProperty<detail::QueueEnableProfiling> {};
-} // namespace queue
-} // namespace property
+} // namespace property::queue
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
-namespace property {
-namespace queue {
+namespace property::queue {
 class discard_events
     : public ::sycl::detail::DataLessProperty<::sycl::detail::DiscardEvents> {};
 
@@ -37,22 +33,15 @@ class priority_low
 class priority_high
     : public sycl::detail::DataLessProperty<sycl::detail::QueuePriorityHigh> {};
 
-} // namespace queue
-} // namespace property
+} // namespace property::queue
 
-namespace cuda {
-namespace property {
-namespace queue {
+namespace cuda::property::queue {
 class use_default_stream : public ::sycl::detail::DataLessProperty<
                                ::sycl::detail::UseDefaultStream> {};
-} // namespace queue
-} // namespace property
-} // namespace cuda
-} // namespace oneapi
-} // namespace ext
+} // namespace cuda::property::queue
+} // namespace ext::oneapi
 
-namespace property {
-namespace queue {
+namespace property ::queue {
 namespace __SYCL2020_DEPRECATED(
     "use 'sycl::ext::oneapi::cuda::property::queue' instead") cuda {
 class use_default_stream
@@ -60,8 +49,7 @@ class use_default_stream
 // clang-format off
 } // namespace cuda
 // clang-format on
-} // namespace queue
-} // namespace property
+} // namespace property::queue
 
 // Forward declaration
 class queue;
diff --git a/sycl/include/sycl/properties/reduction_properties.hpp b/sycl/include/sycl/properties/reduction_properties.hpp
index 8faf5713988ec..ee544a4c3bd9f 100644
--- a/sycl/include/sycl/properties/reduction_properties.hpp
+++ b/sycl/include/sycl/properties/reduction_properties.hpp
@@ -14,12 +14,10 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace property {
-namespace reduction {
+namespace property::reduction {
 class initialize_to_identity
     : public detail::DataLessProperty<detail::InitializeToIdentity> {};
-} // namespace reduction
-} // namespace property
+} // namespace property::reduction
 
 // Reduction property trait specializations
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
diff --git a/sycl/include/sycl/property_list.hpp b/sycl/include/sycl/property_list.hpp
index a28199aeb8d87..367b91e7ff463 100644
--- a/sycl/include/sycl/property_list.hpp
+++ b/sycl/include/sycl/property_list.hpp
@@ -14,11 +14,9 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 template <typename... PropsT> class accessor_property_list;
-}
-} // namespace ext
+} // namespace ext::oneapi
 
 /// Objects of the property_list class are containers for the SYCL properties
 ///
diff --git a/sycl/include/sycl/reduction.hpp b/sycl/include/sycl/reduction.hpp
index a80d69a7af735..0003294740b6e 100644
--- a/sycl/include/sycl/reduction.hpp
+++ b/sycl/include/sycl/reduction.hpp
@@ -1853,11 +1853,9 @@ void reduCGFuncImplArray(
    ...);
 }
 
-namespace reduction {
-namespace main_krn {
+namespace reduction::main_krn {
 template <class KernelName, class Accessor> struct NDRangeMulti;
-} // namespace main_krn
-} // namespace reduction
+} // namespace reduction::main_krn
 template <typename KernelName, typename KernelType, int Dims,
           typename PropertiesT, typename... Reductions, size_t... Is>
 void reduCGFuncMulti(handler &CGH, KernelType KernelFunc,
@@ -2103,11 +2101,9 @@ void reduAuxCGFuncImplArray(
    ...);
 }
 
-namespace reduction {
-namespace aux_krn {
+namespace reduction::aux_krn {
 template <class KernelName, class Predicate> struct Multi;
-} // namespace aux_krn
-} // namespace reduction
+} // namespace reduction::aux_krn
 template <typename KernelName, typename KernelType, typename... Reductions,
           size_t... Is>
 size_t reduAuxCGFunc(handler &CGH, size_t NWorkItems, size_t MaxWGSize,
diff --git a/sycl/include/sycl/sub_group.hpp b/sycl/include/sycl/sub_group.hpp
index 35ca466430d27..a7d53b55bf909 100644
--- a/sycl/include/sycl/sub_group.hpp
+++ b/sycl/include/sycl/sub_group.hpp
@@ -17,9 +17,7 @@ using ext::oneapi::sub_group;
 // TODO move the entire sub_group class implementation to this file once
 // breaking changes are allowed.
 
-namespace ext {
-namespace oneapi {
-namespace experimental {
+namespace ext::oneapi::experimental {
 inline sub_group this_sub_group() {
 #ifdef __SYCL_DEVICE_ONLY__
   return sub_group();
@@ -28,8 +26,6 @@ inline sub_group this_sub_group() {
                       PI_ERROR_INVALID_DEVICE);
 #endif
 }
-} // namespace experimental
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/source/backend/level_zero.cpp b/sycl/source/backend/level_zero.cpp
index baad64a519b38..06321fb5aa866 100644
--- a/sycl/source/backend/level_zero.cpp
+++ b/sycl/source/backend/level_zero.cpp
@@ -15,9 +15,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace level_zero {
+namespace ext::oneapi::level_zero {
 using namespace detail;
 
 //----------------------------------------------------------------------------
@@ -90,8 +88,6 @@ __SYCL_EXPORT event make_event(const context &Context,
                             backend::ext_oneapi_level_zero);
 }
 
-} // namespace level_zero
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::level_zero
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/source/detail/device_global_map.cpp b/sycl/source/detail/device_global_map.cpp
index 690e8f8bfdb0b..952588745fc3b 100644
--- a/sycl/source/detail/device_global_map.cpp
+++ b/sycl/source/detail/device_global_map.cpp
@@ -10,15 +10,13 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace detail {
-namespace device_global_map {
+namespace detail::device_global_map {
 
 __SYCL_EXPORT void add(const void *DeviceGlobalPtr, const char *UniqueId) {
   detail::ProgramManager::getInstance().addOrInitDeviceGlobalEntry(
       DeviceGlobalPtr, UniqueId);
 }
 
-} // namespace device_global_map
-} // namespace detail
+} // namespace detail::device_global_map
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/source/detail/error_handling/enqueue_kernel.cpp b/sycl/source/detail/error_handling/enqueue_kernel.cpp
index da45b2ec509b4..f79b5d914e1f5 100644
--- a/sycl/source/detail/error_handling/enqueue_kernel.cpp
+++ b/sycl/source/detail/error_handling/enqueue_kernel.cpp
@@ -18,9 +18,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace detail {
-
-namespace enqueue_kernel_launch {
+namespace detail::enqueue_kernel_launch {
 
 void handleInvalidWorkGroupSize(const device_impl &DeviceImpl, pi_kernel Kernel,
                                 const NDRDescT &NDRDesc) {
@@ -358,8 +356,6 @@ void handleErrorOrWarning(pi_result Error, const device_impl &DeviceImpl,
   }
 }
 
-} // namespace enqueue_kernel_launch
-
-} // namespace detail
+} // namespace detail::enqueue_kernel_launch
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/source/detail/filter_selector_impl.cpp b/sycl/source/detail/filter_selector_impl.cpp
index 5ed55aff47db2..8e2c6e49863d3 100644
--- a/sycl/source/detail/filter_selector_impl.cpp
+++ b/sycl/source/detail/filter_selector_impl.cpp
@@ -21,9 +21,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace oneapi {
-namespace detail {
+namespace ext::oneapi::detail {
 
 std::vector<std::string> tokenize(const std::string &Filter,
                                   const std::string &Delim) {
@@ -167,9 +165,7 @@ void filter_selector_impl::reset() const {
   mNumDevicesSeen = 0;
 }
 
-} // namespace detail
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi::detail
 
 namespace __SYCL2020_DEPRECATED("use 'ext::oneapi' instead") ONEAPI {
 using namespace ext::oneapi;
diff --git a/sycl/source/detail/fusion/fusion_wrapper.cpp b/sycl/source/detail/fusion/fusion_wrapper.cpp
index 2dd993837401f..708351fae4cfd 100644
--- a/sycl/source/detail/fusion/fusion_wrapper.cpp
+++ b/sycl/source/detail/fusion/fusion_wrapper.cpp
@@ -13,9 +13,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace codeplay {
-namespace experimental {
+namespace ext::codeplay::experimental {
 
 fusion_wrapper::fusion_wrapper(queue &Queue) {
   if (!Queue.ext_codeplay_supports_fusion()) {
@@ -43,8 +41,6 @@ event fusion_wrapper::complete_fusion(const property_list &PropList) {
   return MImpl->complete_fusion(PropList);
 }
 
-} // namespace experimental
-} // namespace codeplay
-} // namespace ext
+} // namespace ext::codeplay::experimental
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/source/detail/online_compiler/online_compiler.cpp b/sycl/source/detail/online_compiler/online_compiler.cpp
index 4fd82e9377cb7..8980c30e531e8 100644
--- a/sycl/source/detail/online_compiler/online_compiler.cpp
+++ b/sycl/source/detail/online_compiler/online_compiler.cpp
@@ -16,9 +16,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace ext {
-namespace intel {
-namespace experimental {
+namespace ext::intel::experimental {
 namespace detail {
 
 static std::vector<const char *>
@@ -236,9 +234,7 @@ __SYCL_EXPORT std::vector<byte> online_compiler<source_language::cm>::compile(
                                 DeviceStepping, CompileToSPIRVHandle,
                                 FreeSPIRVOutputsHandle, CMUserArgs);
 }
-} // namespace experimental
-} // namespace intel
-} // namespace ext
+} // namespace ext::intel::experimental
 
 namespace ext {
 namespace __SYCL2020_DEPRECATED(
diff --git a/sycl/source/detail/posix_pi.cpp b/sycl/source/detail/posix_pi.cpp
index 8fb2849e9b904..92c13edc9791d 100644
--- a/sycl/source/detail/posix_pi.cpp
+++ b/sycl/source/detail/posix_pi.cpp
@@ -14,8 +14,7 @@
 
 namespace sycl {
 __SYCL_INLINE_VER_NAMESPACE(_V1) {
-namespace detail {
-namespace pi {
+namespace detail::pi {
 
 void *loadOsLibrary(const std::string &PluginPath) {
   // TODO: Check if the option RTLD_NOW is correct. Explore using
@@ -41,7 +40,6 @@ void *getOsLibraryFuncAddress(void *Library, const std::string &FunctionName) {
   return dlsym(Library, FunctionName.c_str());
 }
 
-} // namespace pi
-} // namespace detail
+} // namespace detail::pi
 } // __SYCL_INLINE_VER_NAMESPACE(_V1)
 } // namespace sycl
diff --git a/sycl/source/detail/usm/usm_impl.cpp b/sycl/source/detail/usm/usm_impl.cpp
index 4b52529284cf3..6d5227f7b7536 100644
--- a/sycl/source/detail/usm/usm_impl.cpp
+++ b/sycl/source/detail/usm/usm_impl.cpp
@@ -43,8 +43,7 @@ __SYCL_INLINE_VER_NAMESPACE(_V1) {
 
 using alloc = sycl::usm::alloc;
 
-namespace detail {
-namespace usm {
+namespace detail::usm {
 
 void *alignedAllocHost(size_t Alignment, size_t Size, const context &Ctxt,
                        alloc Kind, const property_list &PropList,
@@ -235,8 +234,7 @@ void free(void *Ptr, const context &Ctxt,
   }
 }
 
-} // namespace usm
-} // namespace detail
+} // namespace detail::usm
 
 void *malloc_device(size_t Size, const device &Dev,
                     const context &Ctxt _CODELOCPARAMDEF(&CodeLoc)) {
diff --git a/sycl/source/device_selector.cpp b/sycl/source/device_selector.cpp
index 6493e73d6fcd6..8997ad45208c7 100644
--- a/sycl/source/device_selector.cpp
+++ b/sycl/source/device_selector.cpp
@@ -293,8 +293,7 @@ int accelerator_selector::operator()(const device &dev) const {
   return accelerator_selector_v(dev);
 }
 
-namespace ext {
-namespace oneapi {
+namespace ext::oneapi {
 
 filter_selector::filter_selector(const std::string &Input)
     : impl(std::make_shared<detail::filter_selector_impl>(Input)) {}
@@ -325,8 +324,7 @@ device filter_selector::select_device() const {
   return Result;
 }
 
-} // namespace oneapi
-} // namespace ext
+} // namespace ext::oneapi
 
 namespace __SYCL2020_DEPRECATED("use 'ext::oneapi' instead") ONEAPI {
 using namespace ext::oneapi;