diff --git a/include/mujoco/mjdata.h b/include/mujoco/mjdata.h
index 800aefa3..c2fddb81 100644
--- a/include/mujoco/mjdata.h
+++ b/include/mujoco/mjdata.h
@@ -198,11 +198,6 @@ typedef struct mjData_ {
   // sleep state
   int*    tree_asleep;       // <0: awake; >=0: index cycle of sleeping trees    (ntree x 1)
 
-  // opaque internal island topology cache; users must not modify
-  int* island_cache_tree;    // tree and island topology                         (ntree x 28)
-  int* island_cache_dof;     // DOF topology                                     (nv x 8)
-  int* island_cache_eq;      // equality topology                                (neq x 40)
-
   // plugins
   int*       plugin;         // copy of m->plugin, required for deletion         (nplugin x 1)
   uintptr_t* plugin_data;    // pointer to plugin-managed data structure         (nplugin x 1)
diff --git a/include/mujoco/mjxmacro.h b/include/mujoco/mjxmacro.h
index 71f8ed39..8f36c166 100644
--- a/include/mujoco/mjxmacro.h
+++ b/include/mujoco/mjxmacro.h
@@ -929,10 +929,7 @@
     X   ( mjtNum,    qfrc_inverse,      nv,          1           ) \
     X   ( mjtNum,    cacc,              nbody,       6           ) \
     X   ( mjtNum,    cfrc_int,          nbody,       6           ) \
-    X   ( mjtNum,    cfrc_ext,          nbody,       6           ) \
-    XIC ( int,       island_cache_tree, ntree,       28          ) \
-    XIC ( int,       island_cache_dof,  nv,          8           ) \
-    XIC ( int,       island_cache_eq,   neq,         40          )
+    X   ( mjtNum,    cfrc_ext,          nbody,       6           )
 
 
 // macro for annotating that an array size in an X macro is a member of mjData
@@ -1083,6 +1080,5 @@
 // to obtain only X macros for fields that are relevant for mjvScene creation,
 // redefine XNV to expand to nothing
 #define XNV X
-#define XIC(type, name, nr, nc)
 
 #endif  // MUJOCO_MJXMACRO_H_
diff --git a/src/engine/engine_io.c b/src/engine/engine_io.c
index 285561fb..482f5915 100644
--- a/src/engine/engine_io.c
+++ b/src/engine/engine_io.c
@@ -998,11 +998,7 @@ static void mj_setPtrData(const mjModel* m, mjData* d) {
   ASAN_POISON_MEMORY_REGION(ptr, PTRDIFF(d->name, ptr));  \
   ptr += SKIP((intptr_t)ptr) + sizeof(type)*(m->nr)*(nc);
 
-  #undef XIC
-  #define XIC X
   MJDATA_POINTERS
-  #undef XIC
-  #define XIC(type, name, nr, nc)
 #undef X
 
   // check size
@@ -1089,11 +1085,7 @@ void mj_makeRawData(mjData** dest, const mjModel* m) {
     return;                                                                  \
   }
 
-  #undef XIC
-  #define XIC X
   MJDATA_POINTERS
-  #undef XIC
-  #define XIC(type, name, nr, nc)
 #undef X
 
   // copy stack size from model
@@ -1116,9 +1108,6 @@ void mj_makeRawData(mjData** dest, const mjModel* m) {
 
   // set pointers into buffer
   mj_setPtrData(m, d);
-  if (m->ntree) {
-    d->island_cache_tree[0] = 0;
-  }
 
   // clear threadpool
   d->threadpool = 0;
@@ -1184,9 +1173,6 @@ mjData* mj_copyDataVisual(mjData* dest, const mjModel* m, const mjData* src, int
   dest->arena = save_arena;
   dest->threadpool = 0;
   mj_setPtrData(m, dest);
-  if (m->ntree) {
-    dest->island_cache_tree[0] = 0;
-  }
 
   // save plugin_data, since the X macro copying block below will override it
   const size_t plugin_data_size = sizeof(*dest->plugin_data) * dest->nplugin;
@@ -1387,32 +1373,19 @@ static void _resetData(const mjModel* m, mjData* d, unsigned char debug_value) {
   // fill buffer with debug_value (normally 0)
 #ifdef ADDRESS_SANITIZER
   {
-    #undef XIC
-    #define XIC(type, name, nr, nc)
     #define X(type, name, nr, nc) memset(d->name, (int)debug_value, sizeof(type)*(m->nr)*(nc));
     MJDATA_POINTERS
     #undef X
-    #undef XIC
-    #define XIC(type, name, nr, nc)
   }
 #else
-  size_t cache_offset = d->island_cache_tree ?
-      (size_t)PTRDIFF(d->island_cache_tree, d->buffer) : d->nbuffer;
-  memset(d->buffer, (int)debug_value, cache_offset);
+  memset(d->buffer, (int)debug_value, d->nbuffer);
 #endif
 
 #ifdef MEMORY_SANITIZER
   // under MSAN, mark the entire buffer as uninitialized
   __msan_allocated_memory(d->buffer, d->nbuffer);
-  if (m->ntree) {
-    d->island_cache_tree[0] = 0;
-  }
 #endif
 
-  if (debug_value && m->ntree) {
-    d->island_cache_tree[0] = 0;
-  }
-
   // zero out user-settable state and input arrays (MSAN: mark as initialized)
   mju_zero(d->qpos, m->nq);
   mju_zero(d->qvel, m->nv);
diff --git a/src/engine/engine_island.c b/src/engine/engine_island.c
index 207ccad8..34403b11 100644
--- a/src/engine/engine_island.c
+++ b/src/engine/engine_island.c
@@ -14,10 +14,8 @@
 
 #include "engine/engine_island.h"
 
-#include <stdint.h>
 #include <stdio.h>
 #include <stddef.h>
-#include <string.h>
 
 #include <mujoco/mjdata.h>
 #include <mujoco/mjmodel.h>
@@ -429,211 +427,6 @@ static void assignConstraintIslands(const mjModel* m, mjData* d, const int* tree
 }
 
 
-enum {
-  kCacheMagic = 0x49534C44,
-  kCacheHeader = 16,
-};
-
-typedef struct mjIslandCacheView_ {
-  int* tree_island;
-  int* island_ntree;
-  int* island_itreeadr;
-  int* map_itree2tree;
-  int* island_nv;
-  int* island_idofadr;
-  int* island_dofadr;
-  int* island_ne;
-  int* island_nf;
-  int* island_nefc;
-  int* island_iefcadr;
-  int* tree_dofnum;
-  int* dof_treeid;
-  int* dof_island;
-  int* map_dof2idof;
-  int* map_idof2dof;
-  int* efc_island;
-  int* efc_type;
-  int* efc_id;
-  int* map_efc2iefc;
-  int* map_iefc2efc;
-  int* eq_active;
-  int* eq_type;
-  int* eq_tree1;
-  int* eq_tree2;
-} mjIslandCacheView;
-
-static mjIslandCacheView islandCacheView(const mjModel* m, const mjData* d) {
-  int* tree = d->island_cache_tree + kCacheHeader;
-  int* dof = d->island_cache_dof;
-  int* eq = d->island_cache_eq;
-  int nisland = d->island_cache_tree[4];
-  int nefc = d->island_cache_tree[3];
-  mjIslandCacheView view;
-#define TAKE(base, name, count) view.name = base; base += (count)
-  TAKE(tree, tree_island, m->ntree);
-  TAKE(tree, island_ntree, nisland);
-  TAKE(tree, island_itreeadr, nisland);
-  TAKE(tree, map_itree2tree, m->ntree);
-  TAKE(tree, island_nv, nisland);
-  TAKE(tree, island_idofadr, nisland);
-  TAKE(tree, island_dofadr, nisland);
-  TAKE(tree, island_ne, nisland);
-  TAKE(tree, island_nf, nisland);
-  TAKE(tree, island_nefc, nisland);
-  TAKE(tree, island_iefcadr, nisland);
-  TAKE(tree, tree_dofnum, m->ntree);
-  TAKE(dof, dof_treeid, m->nv);
-  TAKE(dof, dof_island, m->nv);
-  TAKE(dof, map_dof2idof, m->nv);
-  TAKE(dof, map_idof2dof, m->nv);
-  TAKE(eq, efc_island, nefc);
-  TAKE(eq, efc_type, nefc);
-  TAKE(eq, efc_id, nefc);
-  TAKE(eq, map_efc2iefc, nefc);
-  TAKE(eq, map_iefc2efc, nefc);
-  TAKE(eq, eq_active, m->neq);
-  TAKE(eq, eq_type, m->neq);
-  TAKE(eq, eq_tree1, m->neq);
-  TAKE(eq, eq_tree2, m->neq);
-#undef TAKE
-  return view;
-}
-
-static int islandCacheMatches(const mjModel* m, const mjData* d) {
-  if (!m->ntree || !m->neq || d->island_cache_tree[0] != kCacheMagic ||
-      d->island_cache_tree[1] != m->ntree || d->island_cache_tree[2] != m->nv ||
-      d->island_cache_tree[3] != d->nefc || d->island_cache_tree[6] != m->neq ||
-      d->nefc != d->ne || d->nefc < 0 || (int64_t)d->nefc > 6*(int64_t)m->neq ||
-      d->island_cache_tree[4] < 0 || d->island_cache_tree[4] > m->ntree ||
-      d->island_cache_tree[5] < 0 || d->island_cache_tree[5] > m->nv) {
-    return 0;
-  }
-  mjIslandCacheView view = islandCacheView(m, d);
-  if (memcmp(view.efc_type, d->efc_type, d->nefc*sizeof(int)) ||
-      memcmp(view.efc_id, d->efc_id, d->nefc*sizeof(int)) ||
-      memcmp(view.dof_treeid, m->dof_treeid, m->nv*sizeof(int)) ||
-      memcmp(view.tree_dofnum, m->tree_dofnum, m->ntree*sizeof(int))) {
-    return 0;
-  }
-  for (int i=0; i < m->neq; i++) {
-    if (view.eq_active[i] != d->eq_active[i] || view.eq_type[i] != m->eq_type[i] ||
-        (m->eq_type[i] != mjEQ_CONNECT && m->eq_type[i] != mjEQ_WELD)) {
-      return 0;
-    }
-    int obj1 = m->eq_obj1id[i];
-    int obj2 = m->eq_obj2id[i];
-    if (m->eq_objtype[i] == mjOBJ_SITE) {
-      obj1 = m->site_bodyid[obj1];
-      obj2 = m->site_bodyid[obj2];
-    }
-    if (view.eq_tree1[i] != m->body_treeid[obj1] ||
-        view.eq_tree2[i] != m->body_treeid[obj2]) {
-      return 0;
-    }
-  }
-  return 1;
-}
-
-static void restoreIslandCache(const mjModel* m, mjData* d) {
-  mjIslandCacheView view = islandCacheView(m, d);
-#define RESTORE(name, count) mju_copyInt(d->name, view.name, (count))
-  RESTORE(tree_island, m->ntree);
-  RESTORE(island_ntree, d->nisland);
-  RESTORE(island_itreeadr, d->nisland);
-  RESTORE(map_itree2tree, m->ntree);
-  RESTORE(dof_island, m->nv);
-  RESTORE(island_nv, d->nisland);
-  RESTORE(island_idofadr, d->nisland);
-  RESTORE(island_dofadr, d->nisland);
-  RESTORE(map_dof2idof, m->nv);
-  RESTORE(map_idof2dof, m->nv);
-  RESTORE(efc_island, d->nefc);
-  RESTORE(island_ne, d->nisland);
-  RESTORE(island_nf, d->nisland);
-  RESTORE(island_nefc, d->nisland);
-  RESTORE(island_iefcadr, d->nisland);
-  RESTORE(map_efc2iefc, d->nefc);
-  RESTORE(map_iefc2efc, d->nefc);
-#undef RESTORE
-}
-
-static void saveIslandCache(const mjModel* m, mjData* d) {
-  if (!m->ntree || !m->neq || d->nefc != d->ne ||
-      (int64_t)d->nefc > 6*(int64_t)m->neq) {
-    if (m->ntree) d->island_cache_tree[0] = 0;
-    return;
-  }
-  d->island_cache_tree[0] = 0;
-  d->island_cache_tree[1] = m->ntree;
-  d->island_cache_tree[2] = m->nv;
-  d->island_cache_tree[3] = d->nefc;
-  d->island_cache_tree[4] = d->nisland;
-  d->island_cache_tree[5] = d->nidof;
-  d->island_cache_tree[6] = m->neq;
-  d->island_cache_tree[7] = 1;
-  mjIslandCacheView view = islandCacheView(m, d);
-  for (int i=0; i < m->neq; i++) {
-    view.eq_active[i] = d->eq_active[i];
-    view.eq_type[i] = m->eq_type[i];
-    if (m->eq_type[i] != mjEQ_CONNECT && m->eq_type[i] != mjEQ_WELD) return;
-    int obj1 = m->eq_obj1id[i];
-    int obj2 = m->eq_obj2id[i];
-    if (m->eq_objtype[i] == mjOBJ_SITE) {
-      obj1 = m->site_bodyid[obj1];
-      obj2 = m->site_bodyid[obj2];
-    }
-    view.eq_tree1[i] = m->body_treeid[obj1];
-    view.eq_tree2[i] = m->body_treeid[obj2];
-  }
-#define SAVE(name, count) mju_copyInt(view.name, d->name, (count))
-  SAVE(tree_island, m->ntree);
-  SAVE(island_ntree, d->nisland);
-  SAVE(island_itreeadr, d->nisland);
-  SAVE(map_itree2tree, m->ntree);
-  SAVE(dof_island, m->nv);
-  SAVE(island_nv, d->nisland);
-  SAVE(island_idofadr, d->nisland);
-  SAVE(island_dofadr, d->nisland);
-  SAVE(map_dof2idof, m->nv);
-  SAVE(map_idof2dof, m->nv);
-  SAVE(efc_island, d->nefc);
-  SAVE(island_ne, d->nisland);
-  SAVE(island_nf, d->nisland);
-  SAVE(island_nefc, d->nisland);
-  SAVE(island_iefcadr, d->nisland);
-  SAVE(map_efc2iefc, d->nefc);
-  SAVE(map_iefc2efc, d->nefc);
-  mju_copyInt(view.efc_type, d->efc_type, d->nefc);
-  mju_copyInt(view.efc_id, d->efc_id, d->nefc);
-  mju_copyInt(view.dof_treeid, m->dof_treeid, m->nv);
-  mju_copyInt(view.tree_dofnum, m->tree_dofnum, m->ntree);
-#undef SAVE
-  for (int i=0; i < d->nefc; i++) {
-    if (d->map_iefc2efc[i] != i) {
-      d->island_cache_tree[7] = 0;
-      break;
-    }
-  }
-  d->island_cache_tree[0] = kCacheMagic;
-}
-
-static void copyIslandEfcVectors(mjData* d) {
-  if (d->island_cache_tree[0] == kCacheMagic && d->island_cache_tree[7]) {
-    d->iefc_type = d->efc_type;
-    d->iefc_id = d->efc_id;
-    d->iefc_frictionloss = d->efc_frictionloss;
-    d->iefc_D = d->efc_D;
-    d->iefc_R = d->efc_R;
-    return;
-  }
-  mju_gatherInt(d->iefc_type, d->efc_type, d->map_iefc2efc, d->nefc);
-  mju_gatherInt(d->iefc_id, d->efc_id, d->map_iefc2efc, d->nefc);
-  mju_gather(d->iefc_frictionloss, d->efc_frictionloss, d->map_iefc2efc, d->nefc);
-  mju_gather(d->iefc_D, d->efc_D, d->map_iefc2efc, d->nefc);
-  mju_gather(d->iefc_R, d->efc_R, d->map_iefc2efc, d->nefc);
-}
-
-
 //-------------------------- main entry-point  -----------------------------------------------------
 
 // discover islands:
@@ -647,16 +440,6 @@ void mj_island(const mjModel* m, mjData* d) {
     return;
   }
 
-  // exact fast path for topology-stable connect/weld equality constraints
-  if (islandCacheMatches(m, d)) {
-    d->nisland = d->island_cache_tree[4];
-    d->nidof = d->island_cache_tree[5];
-    if (!arenaAllocIsland(m, d)) return;
-    restoreIslandCache(m, d);
-    copyIslandEfcVectors(d);
-    return;
-  }
-
   mj_markStack(d);
 
   // union direct tree incidence and assign deterministic components
@@ -822,6 +605,5 @@ void mj_island(const mjModel* m, mjData* d) {
   // SHOULD NOT OCCUR
   if (!mju_compare(island_nefc2, d->island_nefc, nisland)) mjERROR("island_nefc miscount");
 
-  saveIslandCache(m, d);
   mj_freeStack(d);
 }
diff --git a/test/engine/engine_island_test.cc b/test/engine/engine_island_test.cc
index 00762da2..3a4462ab 100644
--- a/test/engine/engine_island_test.cc
+++ b/test/engine/engine_island_test.cc
@@ -295,69 +295,6 @@ TEST_F(IslandTest, ProductionFlexEqualityRescansRows) {
   EXPECT_THAT(AsVector(data->map_iefc2efc, data->nefc), ElementsAre(0, 1));
 }
 
-TEST_F(IslandTest, EqualityTopologyCacheInvalidatesExactly) {
-  static constexpr char xml[] = R"(
-<mujoco>
-  <option jacobian="sparse"><flag contact="disable" gravity="disable"/></option>
-  <worldbody>
-    <body name="b0"><joint type="slide"/><geom size=".1"/></body>
-    <body name="b1"><joint type="slide"/><geom size=".1"/></body>
-    <body name="b2"><joint type="slide"/><geom size=".1"/></body>
-  </worldbody>
-  <equality>
-    <connect body1="b0" body2="b1" anchor="0 0 0"/>
-    <connect body1="b1" body2="b2" anchor="0 0 0"/>
-  </equality>
-</mujoco>
-)";
-  char error[1024] = {};
-  MjModelPtr model = LoadModelFromString(xml, error, sizeof(error));
-  ASSERT_THAT(model.get(), NotNull()) << error;
-  MjDataPtr data = MakeData(model);
-
-  auto expect_all_connected = [&] {
-    EXPECT_EQ(data->nisland, 1);
-    EXPECT_EQ(data->nidof, 3);
-    EXPECT_EQ(data->nefc, 6);
-    EXPECT_THAT(AsVector(data->tree_island, model->ntree),
-                ElementsAre(0, 0, 0));
-    EXPECT_THAT(AsVector(data->dof_island, model->nv), ElementsAre(0, 0, 0));
-    EXPECT_THAT(AsVector(data->efc_island, data->nefc),
-                ElementsAre(0, 0, 0, 0, 0, 0));
-  };
-
-  // Identical topology is stable across repeated evaluation and ordinary reset.
-  mj_fwdPosition(model.get(), data.get());
-  expect_all_connected();
-  mj_fwdPosition(model.get(), data.get());
-  expect_all_connected();
-
-  // Copying a warm cache produces independent data with the same result.
-  MjDataPtr copy(mj_copyData(nullptr, model.get(), data.get()));
-  ASSERT_THAT(copy.get(), NotNull());
-  mj_fwdPosition(model.get(), copy.get());
-  EXPECT_THAT(AsVector(copy->tree_island, model->ntree),
-              ElementsAre(0, 0, 0));
-
-  mj_resetData(model.get(), data.get());
-  mj_fwdPosition(model.get(), data.get());
-  expect_all_connected();
-
-  // Equality activation changes invalidate the cached partition.
-  data->eq_active[1] = 0;
-  mj_fwdPosition(model.get(), data.get());
-  EXPECT_EQ(data->nisland, 1);
-  EXPECT_EQ(data->nidof, 2);
-  EXPECT_EQ(data->nefc, 3);
-  EXPECT_THAT(AsVector(data->tree_island, model->ntree), ElementsAre(0, 0, -1));
-  EXPECT_THAT(AsVector(data->dof_island, model->nv), ElementsAre(0, 0, -1));
-  EXPECT_THAT(AsVector(data->efc_island, data->nefc), ElementsAre(0, 0, 0));
-
-  // The earlier copy remains independent after the source topology changes.
-  mj_fwdPosition(model.get(), copy.get());
-  EXPECT_THAT(AsVector(copy->tree_island, model->ntree), ElementsAre(0, 0, 0));
-}
-
 TEST_F(IslandTest, BoundedArenaSupports1024Trees) {
   constexpr int kTreeCount = 1024;
   constexpr size_t kArenaBytes = 2 * 1024 * 1024;