diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7594fa2..04b8214 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -30,6 +30,13 @@ option(
     OFF
 )
 
+# Enable P3698
+option(
+    BEMAN_INPLACE_VECTOR_CROSS_CAPACITY_COMPARISON
+    "Enable comparison operators between vectors of different capacities. Default: OFF. Values: { ON, OFF }."
+    OFF
+)
+
 configure_file(
     "${PROJECT_SOURCE_DIR}/include/beman/inplace_vector/config_generated.hpp.in"
     "${PROJECT_BINARY_DIR}/include/beman/inplace_vector/config_generated.hpp"
diff --git a/include/beman/inplace_vector/config.hpp b/include/beman/inplace_vector/config.hpp
index 01aa0ca..673a293 100644
--- a/include/beman/inplace_vector/config.hpp
+++ b/include/beman/inplace_vector/config.hpp
@@ -8,6 +8,7 @@
 #include <beman/inplace_vector/config_generated.hpp>
 #else
 #define BEMAN_INPLACE_VECTOR_NO_EXCEPTIONS() 0
+#define BEMAN_INPLACE_VECTOR_CROSS_CAPACITY_COMPARISON() 0
 #endif
 
 #endif
diff --git a/include/beman/inplace_vector/config_generated.hpp.in b/include/beman/inplace_vector/config_generated.hpp.in
index b2c8e25..e719a01 100644
--- a/include/beman/inplace_vector/config_generated.hpp.in
+++ b/include/beman/inplace_vector/config_generated.hpp.in
@@ -2,5 +2,6 @@
 #define BEMAN_INPLACE_VECTOR_CONFIG_GENERATED_HPP
 
 #cmakedefine01 BEMAN_INPLACE_VECTOR_NO_EXCEPTIONS()
+#cmakedefine01 BEMAN_INPLACE_VECTOR_CROSS_CAPACITY_COMPARISON()
 
 #endif
diff --git a/include/beman/inplace_vector/inplace_vector.hpp b/include/beman/inplace_vector/inplace_vector.hpp
index dfd004f..03976a8 100644
--- a/include/beman/inplace_vector/inplace_vector.hpp
+++ b/include/beman/inplace_vector/inplace_vector.hpp
@@ -284,6 +284,7 @@ struct inplace_vector_base : private storage::storage_for<T, N> {
   }
 
   // [containers.sequences.inplace_vector.data], data access
+
   constexpr T *data() noexcept { return storage_data(); }
   constexpr const T *data() const noexcept { return storage_data(); }
 
@@ -398,11 +399,6 @@ struct inplace_vector_base : private storage::storage_for<T, N> {
     }
   }
 
-  constexpr friend bool operator==(const inplace_vector_base &x,
-                                   const inplace_vector_base &y) {
-    return x.size() == y.size() && std::ranges::equal(x, y);
-  }
-
   constexpr void swap(inplace_vector_base &x) noexcept(
       N == 0 || (std::is_nothrow_swappable_v<T> &&
                  std::is_nothrow_move_constructible_v<T>))
@@ -420,6 +416,50 @@ struct inplace_vector_base : private storage::storage_for<T, N> {
     x.swap(y);
   }
 
+  // [inplace.vector.comparison], comparison
+
+#if BEMAN_INPLACE_VECTOR_CROSS_CAPACITY_COMPARISON()
+  template <std::size_t M>
+  constexpr friend bool operator==(const inplace_vector_base &x,
+                                   const inplace_vector_base<T, M> &y) {
+    const auto sz = std::min(x.size(), y.size());
+
+    return x.size() == y.size() &&
+           std::ranges::equal(x.begin(), x.begin() + sz, y.begin(),
+                              y.begin() + sz);
+  }
+
+  template <std::size_t M>
+    requires std::three_way_comparable<T> || lessthan_comparable<T>
+  constexpr friend auto operator<=>(const inplace_vector_base &x,
+                                    const inplace_vector_base<T, M> &y) {
+    using result_t = std::conditional_t<std::three_way_comparable<T>,
+                                        std::compare_three_way_result<T>,
+                                        std::strong_ordering>;
+
+    if constexpr (std::three_way_comparable<T>) {
+      return std::lexicographical_compare_three_way(
+          x.begin(), x.end(), y.begin(), y.end(), std::compare_three_way());
+    } else {
+      const auto sz = std::min(x.size(), y.size());
+
+      for (std::size_t i = 0; i < sz; ++i) {
+        if (x[i] < y[i])
+          return result_t::less;
+        if (y[i] < x[i])
+          return result_t::greater;
+        // [container.opt.reqmts] < must be total ordering relationship
+      }
+
+      return x.size() <=> y.size();
+    }
+  }
+#else
+  constexpr friend bool operator==(const inplace_vector_base &x,
+                                   const inplace_vector_base &y) {
+    return x.size() == y.size() && std::ranges::equal(x, y);
+  }
+
   constexpr friend auto operator<=>(const inplace_vector_base &x,
                                     const inplace_vector_base &y)
     requires(details::lessthan_comparable<T>)
@@ -441,6 +481,8 @@ struct inplace_vector_base : private storage::storage_for<T, N> {
     }
   }
 
+#endif
+
   // [containers.sequences.inplace_vector.cons], construct/copy/destroy
 
   constexpr inplace_vector_base() noexcept = default;
@@ -925,6 +967,8 @@ struct inplace_vector : public details::inplace_vector_base<T, N> {
 
 } // namespace freestanding
 
+// [inplace.vector.erasure], erasure
+
 template <typename T, std::size_t N, typename U = T>
 constexpr std::size_t erase(details::inplace_vector_base<T, N> &c,
                             const U &value) {
diff --git a/tests/beman/inplace_vector/CMakeLists.txt b/tests/beman/inplace_vector/CMakeLists.txt
index 83f1186..96a7dd6 100644
--- a/tests/beman/inplace_vector/CMakeLists.txt
+++ b/tests/beman/inplace_vector/CMakeLists.txt
@@ -2,7 +2,7 @@
 
 find_package(GTest REQUIRED)
 
-# Tests
+# External test suite from @Hels15
 add_executable(beman.inplace_vector.test inplace_vector.test.cpp)
 
 target_link_libraries(beman.inplace_vector.test PRIVATE beman.inplace_vector)
@@ -20,6 +20,17 @@ add_test(
     COMMAND beman.inplace_vector.ref-test
 )
 
+# constexpr test
+add_executable(beman.inplace_vector.tests.constexpr constexpr.test.cpp)
+target_link_libraries(
+    beman.inplace_vector.tests.constexpr
+    PRIVATE beman.inplace_vector
+)
+add_test(
+    NAME beman.inplace_vector.tests.constexpr
+    COMMAND beman.inplace_vector.tests.constexpr
+)
+
 # GoogleTest based tests
 include(GoogleTest)
 
@@ -43,7 +54,7 @@ add_gtest(erasure)
 add_gtest(modifiers)
 add_gtest(freestanding)
 
-# only add noexception tests if NO_EXCEPTIONS option is set and compiler supports -fno-exceptions
+# Only add noexception tests if NO_EXCEPTIONS option is set and compiler supports -fno-exceptions
 if(
     BEMAN_INPLACE_VECTOR_NO_EXCEPTIONS
     AND (
@@ -57,14 +68,3 @@ if(
         PRIVATE -fno-exceptions
     )
 endif()
-
-# constexpr test
-add_executable(beman.inplace_vector.tests.constexpr constexpr.test.cpp)
-target_link_libraries(
-    beman.inplace_vector.tests.constexpr
-    PRIVATE beman.inplace_vector
-)
-add_test(
-    NAME beman.inplace_vector.tests.constexpr
-    COMMAND beman.inplace_vector.tests.constexpr
-)
diff --git a/tests/beman/inplace_vector/README.md b/tests/beman/inplace_vector/README.md
index a1993e4..c16c352 100644
--- a/tests/beman/inplace_vector/README.md
+++ b/tests/beman/inplace_vector/README.md
@@ -17,7 +17,7 @@ You can checkout `inplace_vector`'s [current state](https://eel.is/c++draft/inpl
 #### 6.1 Overview
 
 > An inplace_vector is a contiguous container. Its capacity is fixed and its
-elements are stored within the inplace_vector object itself.
+> elements are stored within the inplace_vector object itself.
 
 This is not testable.
 
@@ -26,7 +26,7 @@ This is not testable.
 > An inplace_vector meets all of the requirements of a container ([container.reqmts]),
 > of a reversible container ([container.rev.reqmts]), of a contiguous container,
 > and of a sequence container, including most of the optional sequence
-container requirements ([sequence.reqmts]). The exceptions are the push_front,
+> container requirements ([sequence.reqmts]). The exceptions are the push_front,
 > prepend_range, pop_front, and emplace_front member functions,
 > which are not provided.
 > Descriptions are provided here only for operations on inplace_vector that
@@ -50,7 +50,7 @@ Not tested for now.
 > then no `inplace_vector<T, N>` member functions are usable in
 > constant expressions.
 
-See [constexpr.test.cpp](constexpr.test.cpp),
+See [constexpr.test.cpp](constexpr.test.cpp) -
 note that this test suite only ensure functions are usable in a constexpr
 environment.
 The validity of those functions are tested in the main test suite.
@@ -67,6 +67,7 @@ These are tested with individual functions.
 #### 6.6 Triviality
 
 Let IV denote a specialization of `inplace_vector<T, N>`.
+
 > If N is zero, then IV is trivially copyable and empty,
 > and std​::​is_trivially_default_constructible_v<IV> is true.
 > (Sub-clauses omitted)
diff --git a/tests/beman/inplace_vector/compare.test.cpp b/tests/beman/inplace_vector/compare.test.cpp
index 365251b..a9a2be2 100644
--- a/tests/beman/inplace_vector/compare.test.cpp
+++ b/tests/beman/inplace_vector/compare.test.cpp
@@ -1,8 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
 #include <beman/inplace_vector/inplace_vector.hpp>
 #include <gtest/gtest.h>
 
+#include <beman/inplace_vector/config.hpp>
+
 #include <cmath>
 #include <compare>
 
@@ -17,21 +18,23 @@ template <class T>
 concept lessthan_comparable =
     beman::inplace_vector::details::lessthan_comparable<T>;
 
-template <typename T> struct vec_list {
-  T empty;
+template <typename T, typename U = T> struct vec_list {
+  U empty;
   T base;            // base
-  T copy;            // identical to base
-  T greater;         // greater number of elements
-  T lesser;          // lesser number of elements
-  T bigger;          // bigger value of the elements
-  T smaller;         // smaller value of the elements
-  T greater_smaller; // greater number of elements but smaller values
-  T lesser_bigger;   // lesser number of elements but bigger values
+  U copy;            // identical to base
+  U greater;         // greater number of elements
+  U lesser;          // lesser number of elements
+  U bigger;          // bigger value of the elements
+  U smaller;         // smaller value of the elements
+  U greater_smaller; // greater number of elements but smaller values
+  U lesser_bigger;   // lesser number of elements but bigger values
 };
 
-template <typename T> static void runtests(vec_list<T> &list) {
+template <typename T, typename U = T>
+static void runtests(vec_list<T, U> &list) {
 
   static_assert(std::three_way_comparable<T> || lessthan_comparable<T>);
+  static_assert(std::three_way_comparable<U> || lessthan_comparable<U>);
 
   // if T::value_type is threewaycomparable with ordering X then T must also
   // be comparable with ordering X
@@ -326,3 +329,41 @@ TEST(Compare, threeway_uncomparable) {
   static_assert(!std::three_way_comparable<inplace_vector<uncomparable3, 4>>);
   static_assert(!has_threeway<inplace_vector<uncomparable3, 4>>);
 }
+
+// In accordance with P3698R0, we compare vectors with identical elements but
+// different capacities
+#if BEMAN_INPLACE_VECTOR_CROSS_CAPACITY_COMPARISON()
+
+TEST(Compare, threeway_cross_capacity) {
+  vec_list<inplace_vector<int, 4>, inplace_vector<int, 5>> list{
+      .empty{},
+      .base{1, 2, 3},
+      .copy{1, 2, 3},
+      .greater{4, 5, 6},
+      .lesser{0, 0, 0},
+      .bigger{1, 2, 3, 0},
+      .smaller{1, 2},
+      .greater_smaller{2, 2},
+      .lesser_bigger{0, 2, 3, 4},
+  };
+
+  runtests(list);
+}
+
+TEST(Compare, threeway_cross_capacity_full) {
+  vec_list<inplace_vector<int, 3>, inplace_vector<int, 4>> list{
+      .empty{},
+      .base{1, 2, 3},
+      .copy{1, 2, 3},
+      .greater{4, 5, 6},
+      .lesser{0, 0, 0},
+      .bigger{1, 2, 3, 0},
+      .smaller{1, 2},
+      .greater_smaller{2, 2},
+      .lesser_bigger{0, 2, 3, 4},
+  };
+
+  runtests(list);
+}
+
+#endif
diff --git a/tests/beman/inplace_vector/constexpr.test.cpp b/tests/beman/inplace_vector/constexpr.test.cpp
index ace31b2..e00a284 100644
--- a/tests/beman/inplace_vector/constexpr.test.cpp
+++ b/tests/beman/inplace_vector/constexpr.test.cpp
@@ -1,5 +1,4 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
 #include <beman/inplace_vector/inplace_vector.hpp>
 
 #include <array>
diff --git a/tests/beman/inplace_vector/constructors.test.cpp b/tests/beman/inplace_vector/constructors.test.cpp
index ce53716..0f194ab 100644
--- a/tests/beman/inplace_vector/constructors.test.cpp
+++ b/tests/beman/inplace_vector/constructors.test.cpp
@@ -1,7 +1,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#include <beman/inplace_vector/inplace_vector.hpp>
+#include <gtest/gtest.h>
 
 #include <algorithm>
-#include <gtest/gtest.h>
 #include <numeric>
 
 #include "gtest_setup.hpp"
diff --git a/tests/beman/inplace_vector/container_requirements.test.cpp b/tests/beman/inplace_vector/container_requirements.test.cpp
index 7861af3..5e62843 100644
--- a/tests/beman/inplace_vector/container_requirements.test.cpp
+++ b/tests/beman/inplace_vector/container_requirements.test.cpp
@@ -1,9 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#include <beman/inplace_vector/inplace_vector.hpp>
+#include <gtest/gtest.h>
 
-#include "gtest/gtest.h"
 #include <algorithm>
 #include <array>
-#include <gtest/gtest.h>
 #include <new>
 
 #include "gtest_setup.hpp"
diff --git a/tests/beman/inplace_vector/erasure.test.cpp b/tests/beman/inplace_vector/erasure.test.cpp
index 8a4968c..c5209ad 100644
--- a/tests/beman/inplace_vector/erasure.test.cpp
+++ b/tests/beman/inplace_vector/erasure.test.cpp
@@ -1,7 +1,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#include <beman/inplace_vector/inplace_vector.hpp>
+#include <gtest/gtest.h>
 
 #include <algorithm>
-#include <gtest/gtest.h>
 
 #include "gtest_setup.hpp"
 
diff --git a/tests/beman/inplace_vector/freestanding.test.cpp b/tests/beman/inplace_vector/freestanding.test.cpp
index a26429e..79e6b58 100644
--- a/tests/beman/inplace_vector/freestanding.test.cpp
+++ b/tests/beman/inplace_vector/freestanding.test.cpp
@@ -1,9 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-#include <array>
 #include <beman/inplace_vector/inplace_vector.hpp>
 #include <gtest/gtest.h>
 
+#include <array>
+
 // constexpr void assign(InputIterator first, InputIterator last);
 template <typename T>
 concept has_assign_iterator = requires(T t, T::iterator it) {
diff --git a/tests/beman/inplace_vector/gtest_setup.hpp b/tests/beman/inplace_vector/gtest_setup.hpp
index 87a615f..3b9e849 100644
--- a/tests/beman/inplace_vector/gtest_setup.hpp
+++ b/tests/beman/inplace_vector/gtest_setup.hpp
@@ -1,9 +1,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
+#include <beman/inplace_vector/inplace_vector.hpp>
 #include <gtest/gtest.h>
-#include <type_traits>
 
-#include "beman/inplace_vector/inplace_vector.hpp"
+#include <type_traits>
 
 // We run the tests on various element types with the help of GoogleTest's
 // typed tests. Which types shall we use?
@@ -287,7 +286,7 @@ struct NonTrivial {
   }
   friend constexpr bool operator==(NonTrivial x, NonTrivial y) = default;
 };
-std::size_t NonTrivial::num_objects;
+inline std::size_t NonTrivial::num_objects;
 
 template<typename T, typename = void>
 struct counts_objects : std::false_type {};
diff --git a/tests/beman/inplace_vector/inplace_vector.test.cpp b/tests/beman/inplace_vector/inplace_vector.test.cpp
index 4d3d795..5652b68 100644
--- a/tests/beman/inplace_vector/inplace_vector.test.cpp
+++ b/tests/beman/inplace_vector/inplace_vector.test.cpp
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #include <beman/inplace_vector/inplace_vector.hpp>
+
 #include <cassert>
 
 using namespace beman::inplace_vector;
diff --git a/tests/beman/inplace_vector/modifiers.test.cpp b/tests/beman/inplace_vector/modifiers.test.cpp
index 4f702e3..1891fad 100644
--- a/tests/beman/inplace_vector/modifiers.test.cpp
+++ b/tests/beman/inplace_vector/modifiers.test.cpp
@@ -1,9 +1,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#include <beman/inplace_vector/inplace_vector.hpp>
+#include <gtest/gtest.h>
 
 #include <numeric>
 
 #include "gtest_setup.hpp"
-#include <gtest/gtest.h>
 
 namespace {
 // 23.3.14.5 Modifiers [inplace.vector.modifiers]
diff --git a/tests/beman/inplace_vector/noexceptions.test.cpp b/tests/beman/inplace_vector/noexceptions.test.cpp
index 74d103a..9204791 100644
--- a/tests/beman/inplace_vector/noexceptions.test.cpp
+++ b/tests/beman/inplace_vector/noexceptions.test.cpp
@@ -1,4 +1,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// #include <beman/inplace_vector/inplace_vector.hpp> 'BEMAN_IV_THROW_OR_ABORT'
+// macro redfined
+#include <gtest/gtest.h>
 
 #include <array>
 
diff --git a/tests/beman/inplace_vector/ref_impl.test.cpp b/tests/beman/inplace_vector/ref_impl.test.cpp
index e7f9d1a..c869c06 100644
--- a/tests/beman/inplace_vector/ref_impl.test.cpp
+++ b/tests/beman/inplace_vector/ref_impl.test.cpp
@@ -1,5 +1,4 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
 #pragma GCC diagnostic ignored "-Wsign-compare"
 
 /// \file
diff --git a/tests/beman/inplace_vector/size_n_data.test.cpp b/tests/beman/inplace_vector/size_n_data.test.cpp
index 7b857c6..71f03db 100644
--- a/tests/beman/inplace_vector/size_n_data.test.cpp
+++ b/tests/beman/inplace_vector/size_n_data.test.cpp
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
+#include <beman/inplace_vector/inplace_vector.hpp>
 #include <gtest/gtest.h>
+
 #include <numeric>
 
 #include "gtest_setup.hpp"
diff --git a/tests/beman/inplace_vector/triviality.test.cpp b/tests/beman/inplace_vector/triviality.test.cpp
index 0d8d6f9..2db11a3 100644
--- a/tests/beman/inplace_vector/triviality.test.cpp
+++ b/tests/beman/inplace_vector/triviality.test.cpp
@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
+#include <beman/inplace_vector/inplace_vector.hpp>
 #include <gtest/gtest.h>
 
 #include "gtest_setup.hpp"