diff --git a/include/deemon/object.h b/include/deemon/object.h
index 873e15cb..8bc7dfc3 100644
--- a/include/deemon/object.h
+++ b/include/deemon/object.h
@@ -2111,6 +2111,23 @@ struct Dee_type_seq {
 	WUNUSED_T NONNULL_T((1, 2)) int (DCALL *tp_bounditem_string_len_hash)(DeeObject *self, char const *key, size_t keylen, Dee_hash_t hash);
 	WUNUSED_T NONNULL_T((1, 2)) int (DCALL *tp_hasitem_string_len_hash)(DeeObject *self, char const *key, size_t keylen, Dee_hash_t hash);
 
+	/* Optional helper to help implement `DeeSeq_AsHeapVector()' & friends.
+	 * NOTES:
+	 * - This operator is NOT used to implement stuff above, and will NOT
+	 *   be substituted using other operators. This operator gets inherited
+	 *   alongside "tp_iter", though its presence does not qualify for that
+	 *   operator being present!
+	 * - This operator must NOT produce NULL-elements in "dst". The produced
+	 *   vector of items must be equivalent to what would be produced by a
+	 *   call to "tp_foreach" (which in turn must be equivalent to "tp_iter").
+	 *
+	 * @return: <= dst_length: Success: the first "return" elements of "dst" were filled with the items of this sequence.
+	 * @return: > dst_length:  The given "dst_length" is too short. In this case, "dst" may have been modified,
+	 *                         but will not contain any object references. You must resize it until it is able
+	 *                         to hold at least "return" elements, and call this operator again.
+	 * @return: (size_t)-1:    Error. */
+	WUNUSED_T NONNULL_T((1)) size_t (DCALL *tp_asvector)(DeeObject *self, /*out*/ DREF DeeObject **dst, size_t dst_length);
+
 	/* All of the following are *always* and *unconditionally* implemented
 	 * when the associated type has the "tp_features & TF_KW" flag set,
 	 * with the exception of `DeeKwds_Type', which has that flag, but does
@@ -2484,6 +2501,14 @@ myob_hasitem_string_len_hash(MyObject *self, char const *key, size_t keylen, Dee
 	return DeeError_NOTIMPLEMENTED();
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+myob_asvector(MyObject *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	(void)self;
+	(void)dst;
+	(void)dst_length;
+	return (size_t)DeeError_NOTIMPLEMENTED();
+}
+
 PRIVATE struct type_seq myob_seq = {
 	/* .tp_iter                       = */ (DREF DeeObject *(DCALL *)(DeeObject *__restrict))&myob_iter,
 	/* .tp_sizeob                     = */ (DREF DeeObject *(DCALL *)(DeeObject *__restrict))&myob_sizeob,
@@ -2530,6 +2555,7 @@ PRIVATE struct type_seq myob_seq = {
 	/* .tp_setitem_string_len_hash    = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t, DeeObject *))&myob_setitem_string_len_hash,
 	/* .tp_bounditem_string_len_hash  = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&myob_bounditem_string_len_hash,
 	/* .tp_hasitem_string_len_hash    = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&myob_hasitem_string_len_hash,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&myob_asvector,
 	/* .tp_getitemnr                    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, /*string*/ DeeObject *__restrict))NULL,
 	/* .tp_getitemnr_string_hash        = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, Dee_hash_t))NULL,
 	/* .tp_getitemnr_string_len_hash    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, size_t, Dee_hash_t))NULL,
diff --git a/src/deemon/objects/bytes.c b/src/deemon/objects/bytes.c
index db0318d5..3fe57750 100644
--- a/src/deemon/objects/bytes.c
+++ b/src/deemon/objects/bytes.c
@@ -1406,6 +1406,29 @@ bytes_foreach(Bytes *__restrict self, Dee_foreach_t proc, void *arg) {
 	return temp;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+bytes_asvector(Bytes *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	size_t size = DeeBytes_SIZE(self);
+	if likely(dst_length >= size) {
+		size_t i;
+		for (i = 0; i < size; ++i) {
+			DREF DeeObject *int_value;
+			byte_t value = DeeBytes_DATA(self)[i];
+#ifdef DeeInt_8bit
+			int_value = (DREF DeeObject *)(DeeInt_8bit + value);
+			Dee_Incref(int_value);
+#else /* DeeInt_8bit */
+			int_value = DeeInt_NewUInt8(value);
+			if unlikely(!int_value) {
+				Dee_Decrefv(dst, i);
+				return (size_t)-1;
+			}
+#endif /* !DeeInt_8bit */
+			dst[i] = int_value; /* Inherit reference */
+		}
+	}
+	return size;
+}
 
 PRIVATE struct type_nsi tpconst bytes_nsi = {
 	/* .nsi_class   = */ TYPE_SEQX_CLASS_SEQ,
@@ -1482,6 +1505,7 @@ PRIVATE struct type_seq bytes_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&bytes_asvector,
 };
 
 
diff --git a/src/deemon/objects/cached-dict.c b/src/deemon/objects/cached-dict.c
index 6b7c3845..a0326f18 100644
--- a/src/deemon/objects/cached-dict.c
+++ b/src/deemon/objects/cached-dict.c
@@ -1301,6 +1301,7 @@ PRIVATE struct type_seq cdict_seq = {
 	/* .tp_setitem_string_len_hash      = */ NULL,
 	/* .tp_bounditem_string_len_hash    = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&cdict_bounditem_string_len_hash,
 	/* .tp_hasitem_string_len_hash      = */ NULL,
+	/* .tp_asvector                     = */ NULL,
 	/* .tp_getitemnr                    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, /*string*/ DeeObject *__restrict))&cdict_getitemnr,
 	/* .tp_getitemnr_string_hash        = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, Dee_hash_t))&cdict_getitemnr_string_hash,
 	/* .tp_getitemnr_string_len_hash    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, size_t, Dee_hash_t))&cdict_getitemnr_string_len_hash,
diff --git a/src/deemon/objects/hashset.c b/src/deemon/objects/hashset.c
index c2a6a0c8..46522c31 100644
--- a/src/deemon/objects/hashset.c
+++ b/src/deemon/objects/hashset.c
@@ -1847,6 +1847,26 @@ hashset_printrepr(HashSet *__restrict self,
 	return temp;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+hashset_asvector(HashSet *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	size_t result;
+	DeeHashSet_LockRead(self);
+	result = self->hs_used;
+	if likely(dst_length >= result) {
+		struct hashset_item *iter, *end;
+		end = (iter = self->hs_elem) + (self->hs_mask + 1);
+		for (; iter < end; ++iter) {
+			DeeObject *key = iter->hsi_key;
+			if (key == NULL || key == dummy)
+				continue;
+			Dee_Incref(key);
+			*dst++ = key;
+		}
+	}
+	DeeHashSet_LockEndRead(self);
+	return result;
+}
+
 PRIVATE struct type_nsi tpconst hashset_nsi = {
 	/* .nsi_class   = */ TYPE_SEQX_CLASS_SET,
 	/* .nsi_flags   = */ TYPE_SEQX_FMUTABLE | TYPE_SEQX_FRESIZABLE,
@@ -1903,6 +1923,7 @@ PRIVATE struct type_seq hashset_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&hashset_asvector,
 };
 
 PRIVATE WUNUSED NONNULL((1)) int DCALL
diff --git a/src/deemon/objects/list.c b/src/deemon/objects/list.c
index 90b463aa..85d75c0e 100644
--- a/src/deemon/objects/list.c
+++ b/src/deemon/objects/list.c
@@ -2105,6 +2105,16 @@ list_enumerate_index(List *self, Dee_enumerate_index_t proc,
 	return temp;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+list_asvector(List *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	size_t realsize;
+	DeeList_LockRead(self);
+	realsize = self->l_list.ol_elemc;
+	if likely(dst_length >= realsize)
+		Dee_Movrefv(dst, self->l_list.ol_elemv, realsize);
+	DeeList_LockEndRead(self);
+	return realsize;
+}
 
 PRIVATE struct type_nsi tpconst list_nsi = {
 	/* .nsi_class   = */ TYPE_SEQX_CLASS_SEQ,
@@ -2173,6 +2183,7 @@ PRIVATE struct type_seq list_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&list_asvector,
 };
 
 PRIVATE WUNUSED NONNULL((1, 2)) int DCALL
diff --git a/src/deemon/objects/rodict.c b/src/deemon/objects/rodict.c
index 5fa5d402..b9aec613 100644
--- a/src/deemon/objects/rodict.c
+++ b/src/deemon/objects/rodict.c
@@ -1043,6 +1043,7 @@ PRIVATE struct type_seq rodict_seq = {
 	/* .tp_setitem_string_len_hash      = */ NULL,
 	/* .tp_bounditem_string_len_hash    = */ NULL,
 	/* .tp_hasitem_string_len_hash      = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&rodict_hasitem_string_len_hash,
+	/* .tp_asvector                     = */ NULL,
 	/* .tp_getitemnr                    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, /*string*/ DeeObject *__restrict))&rodict_getitemnr,
 	/* .tp_getitemnr_string_hash        = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, Dee_hash_t))&rodict_getitemnr_string_hash,
 	/* .tp_getitemnr_string_len_hash    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, size_t, Dee_hash_t))&rodict_getitemnr_string_len_hash,
diff --git a/src/deemon/objects/roset.c b/src/deemon/objects/roset.c
index 5c945905..22957e40 100644
--- a/src/deemon/objects/roset.c
+++ b/src/deemon/objects/roset.c
@@ -501,6 +501,22 @@ roset_foreach(RoSet *self, Dee_foreach_t proc, void *arg) {
 	return temp;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+roset_asvector(RoSet *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	if likely(dst_length >= self->rs_size) {
+		struct roset_item *iter, *end;
+		end = (iter = self->rs_elem) + (self->rs_mask + 1);
+		for (; iter < end; ++iter) {
+			DeeObject *key = iter->rsi_key;
+			if (key == NULL)
+				continue;
+			Dee_Incref(key);
+			*dst++ = key;
+		}
+	}
+	return self->rs_size;
+}
+
 PRIVATE struct type_seq roset_seq = {
 	/* .tp_iter                       = */ (DREF DeeObject *(DCALL *)(DeeObject *__restrict))&roset_iter,
 	/* .tp_sizeob                     = */ NULL,
@@ -547,6 +563,7 @@ PRIVATE struct type_seq roset_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&roset_asvector,
 };
 
 PRIVATE WUNUSED NONNULL((1)) DREF DeeObject *DCALL
diff --git a/src/deemon/objects/seq/fastseq.c b/src/deemon/objects/seq/fastseq.c
index 5ed25713..6ea6bfdf 100644
--- a/src/deemon/objects/seq/fastseq.c
+++ b/src/deemon/objects/seq/fastseq.c
@@ -34,6 +34,8 @@
 #include <deemon/thread.h>
 #include <deemon/tuple.h>
 
+#include <hybrid/overflow.h>
+
 #include "../../runtime/runtime_error.h"
 #include "range.h"
 #include "subrange.h"
@@ -285,6 +287,82 @@ foreach_seq_as_heap_vector_cb(void *arg, DeeObject *__restrict elem) {
 PUBLIC WUNUSED NONNULL((1, 2)) /*owned(Dee_Free)*/ DREF DeeObject **DCALL
 DeeSeq_AsHeapVector(DeeObject *__restrict self,
                     size_t *__restrict p_length) {
+#ifdef CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS
+	DeeTypeObject *tp_self = Dee_TYPE(self);
+	struct foreach_seq_as_heap_vector_data data;
+	if unlikely(!(likely(tp_self->tp_seq && tp_self->tp_seq->tp_foreach) ||
+	              unlikely(DeeType_InheritIter(tp_self)))) {
+		err_unimplemented_operator(tp_self, OPERATOR_ITER);
+		goto err;
+	}
+
+	/* Try to use "tp_size_fast" to get a good guess regarding the initial buffer size. */
+	if likely(tp_self->tp_seq->tp_size_fast) {
+		data.sahvd_alloc = (*tp_self->tp_seq->tp_size_fast)(self);
+		if (data.sahvd_alloc == (size_t)-1)
+			data.sahvd_alloc = 16;
+	} else {
+		data.sahvd_alloc = 16;
+	}
+	data.sahvd_vector = (DREF DeeObject **)Dee_TryMallocc(data.sahvd_alloc, sizeof(DREF DeeObject *));
+	if unlikely(!data.sahvd_vector) {
+		data.sahvd_alloc  = 1;
+		data.sahvd_vector = (DREF DeeObject **)Dee_Mallocc(1, sizeof(DREF DeeObject *));
+		if unlikely(!data.sahvd_vector)
+			goto err;
+	}
+
+	/* Check if the type supports the "tp_asvector" extension. */
+	if (tp_self->tp_seq->tp_asvector) {
+		DREF DeeObject **new_vector;
+again_asvector:
+		data.sahvd_size = (*tp_self->tp_seq->tp_asvector)(self, data.sahvd_vector, data.sahvd_alloc);
+		if likely(data.sahvd_size <= data.sahvd_alloc) {
+			if unlikely(data.sahvd_size < data.sahvd_alloc)
+				goto resize_data_and_done;
+			goto done;
+		}
+		if unlikely(data.sahvd_size == (size_t)-1)
+			goto err_vector;
+		/* Need a larger vector buffer. */
+		data.sahvd_alloc = data.sahvd_size;
+		new_vector = (DREF DeeObject **)Dee_Reallocc(data.sahvd_vector,
+		                                             data.sahvd_alloc,
+		                                             sizeof(DREF DeeObject *));
+		if unlikely(!new_vector)
+			goto err_vector;
+		data.sahvd_vector = new_vector;
+		goto again_asvector;
+	}
+
+	/* Fallback: use "tp_foreach" to enumerate sequence items. */
+	data.sahvd_size = 0;
+	if unlikely((*tp_self->tp_seq->tp_foreach)(self, &foreach_seq_as_heap_vector_cb, &data))
+		goto err_vector_data;
+	ASSERT(data.sahvd_size <= data.sahvd_alloc);
+
+	/* Free unused memory. */
+	if (data.sahvd_size < data.sahvd_alloc) {
+		DREF DeeObject **new_vector;
+resize_data_and_done:
+		new_vector = (DREF DeeObject **)Dee_TryReallocc(data.sahvd_vector,
+		                                                data.sahvd_size,
+		                                                sizeof(DREF DeeObject *));
+		if likely(new_vector)
+			data.sahvd_vector = new_vector;
+	}
+
+	/* Save the resulting length. */
+done:
+	*p_length = data.sahvd_size;
+	return data.sahvd_vector;
+err_vector_data:
+	Dee_Decrefv(data.sahvd_vector, data.sahvd_size);
+err_vector:
+	Dee_Free(data.sahvd_vector);
+err:
+	return NULL;
+#else /* CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 	struct foreach_seq_as_heap_vector_data data;
 	data.sahvd_size = DeeFastSeq_GetSize_deprecated(self);
 	if (data.sahvd_size != DEE_FASTSEQ_NOTFAST_DEPRECATED) {
@@ -343,6 +421,7 @@ DeeSeq_AsHeapVector(DeeObject *__restrict self,
 	Dee_Free(data.sahvd_vector);
 err:
 	return NULL;
+#endif /* !CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 }
 
 #ifdef Dee_MallocUsableSize
@@ -371,6 +450,71 @@ DeeSeq_AsHeapVectorWithAlloc(DeeObject *__restrict self,
                              /*[out]*/ size_t *__restrict p_allocated)
 #endif /* !Dee_MallocUsableSize */
 {
+#ifdef CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS
+	DeeTypeObject *tp_self = Dee_TYPE(self);
+	struct foreach_seq_as_heap_vector_data data;
+	if unlikely(!(likely(tp_self->tp_seq && tp_self->tp_seq->tp_foreach) ||
+	              unlikely(DeeType_InheritIter(tp_self)))) {
+		err_unimplemented_operator(tp_self, OPERATOR_ITER);
+		goto err;
+	}
+
+	/* Try to use "tp_size_fast" to get a good guess regarding the initial buffer size. */
+	if likely(tp_self->tp_seq->tp_size_fast) {
+		data.sahvd_alloc = (*tp_self->tp_seq->tp_size_fast)(self);
+		if (data.sahvd_alloc == (size_t)-1)
+			data.sahvd_alloc = 16;
+	} else {
+		data.sahvd_alloc = 16;
+	}
+	data.sahvd_vector = (DREF DeeObject **)Dee_TryMallocc(data.sahvd_alloc, sizeof(DREF DeeObject *));
+	if unlikely(!data.sahvd_vector) {
+		data.sahvd_alloc  = 1;
+		data.sahvd_vector = (DREF DeeObject **)Dee_Mallocc(1, sizeof(DREF DeeObject *));
+		if unlikely(!data.sahvd_vector)
+			goto err;
+	}
+
+	/* Check if the type supports the "tp_asvector" extension. */
+	if (tp_self->tp_seq->tp_asvector) {
+		DREF DeeObject **new_vector;
+again_asvector:
+		data.sahvd_size = (*tp_self->tp_seq->tp_asvector)(self, data.sahvd_vector, data.sahvd_alloc);
+		if likely(data.sahvd_size <= data.sahvd_alloc)
+			goto done;
+		if unlikely(data.sahvd_size == (size_t)-1)
+			goto err_vector;
+		/* Need a larger vector buffer. */
+		data.sahvd_alloc = data.sahvd_size;
+		new_vector = (DREF DeeObject **)Dee_Reallocc(data.sahvd_vector,
+		                                             data.sahvd_alloc,
+		                                             sizeof(DREF DeeObject *));
+		if unlikely(!new_vector)
+			goto err_vector;
+		data.sahvd_vector = new_vector;
+		goto again_asvector;
+	}
+
+	/* Fallback: use "tp_foreach" to enumerate sequence items. */
+	data.sahvd_size = 0;
+	if unlikely((*tp_self->tp_seq->tp_foreach)(self, &foreach_seq_as_heap_vector_cb, &data))
+		goto err_vector_data;
+	ASSERT(data.sahvd_size <= data.sahvd_alloc);
+
+	/* Save the resulting length. */
+done:
+#ifndef Dee_MallocUsableSize
+	*p_allocated = data.sahvd_alloc;
+#endif /* !Dee_MallocUsableSize */
+	*p_length = data.sahvd_size;
+	return data.sahvd_vector;
+err_vector_data:
+	Dee_Decrefv(data.sahvd_vector, data.sahvd_size);
+err_vector:
+	Dee_Free(data.sahvd_vector);
+err:
+	return NULL;
+#else /* CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 	struct foreach_seq_as_heap_vector_data data;
 	data.sahvd_size = DeeFastSeq_GetSize_deprecated(self);
 	if (data.sahvd_size != DEE_FASTSEQ_NOTFAST_DEPRECATED) {
@@ -425,6 +569,7 @@ DeeSeq_AsHeapVectorWithAlloc(DeeObject *__restrict self,
 	Dee_Free(data.sahvd_vector);
 err:
 	return NULL;
+#endif /* !CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 }
 
 
@@ -474,6 +619,78 @@ DeeSeq_AsHeapVectorWithAllocReuse(DeeObject *__restrict self,
                                   /*in-out*/ size_t *__restrict p_allocated)
 #endif /* !Dee_MallocUsableSize */
 {
+#ifdef CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS
+	DeeTypeObject *tp_self = Dee_TYPE(self);
+	struct foreach_seq_as_heap_vector_data data;
+	if unlikely(!(likely(tp_self->tp_seq && tp_self->tp_seq->tp_foreach) ||
+	              unlikely(DeeType_InheritIter(tp_self)))) {
+		err_unimplemented_operator(tp_self, OPERATOR_ITER);
+		goto err;
+	}
+
+	data.sahvd_vector = *p_vector;
+#ifdef Dee_MallocUsableSize
+	data.sahvd_alloc = Dee_MallocUsableSize(data.sahvd_vector) / sizeof(DREF DeeObject *);
+#else /* Dee_MallocUsableSize */
+	data.sahvd_alloc = *p_allocated;
+#endif /* !Dee_MallocUsableSize */
+	ASSERT(!data.sahvd_alloc || data.sahvd_vector);
+
+	/* Try to use "tp_size_fast" to get a good guess regarding the initial buffer size. */
+	if likely(tp_self->tp_seq->tp_size_fast) {
+		size_t min_alloc;
+		min_alloc = (*tp_self->tp_seq->tp_size_fast)(self);
+		if (min_alloc != (size_t)-1 && min_alloc > data.sahvd_alloc) {
+			DREF DeeObject **new_vector;
+			new_vector = (DREF DeeObject **)Dee_TryReallocc(data.sahvd_vector, min_alloc,
+			                                                sizeof(DREF DeeObject *));
+			if likely(new_vector) {
+				data.sahvd_vector = new_vector;
+				data.sahvd_alloc  = min_alloc;
+			}
+		}
+	}
+
+	/* Check if the type supports the "tp_asvector" extension. */
+	if (tp_self->tp_seq->tp_asvector) {
+		DREF DeeObject **new_vector;
+again_asvector:
+		data.sahvd_size = (*tp_self->tp_seq->tp_asvector)(self, data.sahvd_vector, data.sahvd_alloc);
+		if likely(data.sahvd_size <= data.sahvd_alloc)
+			goto done;
+		if unlikely(data.sahvd_size == (size_t)-1)
+			goto done;
+		/* Need a larger vector buffer. */
+		data.sahvd_alloc = data.sahvd_size;
+		new_vector = (DREF DeeObject **)Dee_Reallocc(data.sahvd_vector,
+		                                             data.sahvd_alloc,
+		                                             sizeof(DREF DeeObject *));
+		if unlikely(!new_vector)
+			goto err_writeback;
+		data.sahvd_vector = new_vector;
+		goto again_asvector;
+	}
+
+	/* Fallback: use "tp_foreach" to enumerate sequence items. */
+	data.sahvd_size = 0;
+	if unlikely((*tp_self->tp_seq->tp_foreach)(self, &foreach_seq_as_heap_vector_cb, &data))
+		goto err_writeback_data;
+	ASSERT(data.sahvd_size <= data.sahvd_alloc);
+
+done:
+	*p_vector = data.sahvd_vector;
+#ifndef Dee_MallocUsableSize
+	*p_allocated = data.sahvd_alloc;
+#endif /* !Dee_MallocUsableSize */
+	return data.sahvd_size;
+err_writeback_data:
+	Dee_Decrefv(data.sahvd_vector, data.sahvd_size);
+err_writeback:
+	data.sahvd_size = (size_t)-1;
+	goto done;
+err:
+	return (size_t)-1;
+#else /* CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 	Dee_ssize_t error;
 	struct foreach_seq_as_heap_vector_data data;
 	data.sahvd_vector = *p_vector;
@@ -511,7 +728,7 @@ DeeSeq_AsHeapVectorWithAllocReuse(DeeObject *__restrict self,
 				elem = DeeFastSeq_GetItem_deprecated(self, i);
 				if unlikely(!elem) {
 					data.sahvd_size = i;
-					goto err_data;
+					goto err_writeback_data;
 				}
 				data.sahvd_vector[i] = elem; /* Inherit reference. */
 			}
@@ -528,12 +745,13 @@ DeeSeq_AsHeapVectorWithAllocReuse(DeeObject *__restrict self,
 	*p_allocated = data.sahvd_alloc;
 #endif /* !Dee_MallocUsableSize */
 	if unlikely(error)
-		goto err_data;
+		goto err_writeback_data;
 	return data.sahvd_size;
-err_data:
+err_writeback_data:
 	Dee_Decrefv(data.sahvd_vector, data.sahvd_size);
 err:
 	return (size_t)-1;
+#endif /* !CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 }
 
 
@@ -575,6 +793,93 @@ DeeSeq_AsHeapVectorWithAllocReuseOffset(DeeObject *__restrict self,
                                         /*in*/ size_t offset)
 #endif /* !Dee_MallocUsableSize */
 {
+#ifdef CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS
+	DeeTypeObject *tp_self = Dee_TYPE(self);
+	struct foreach_seq_as_heap_vector_data data;
+	if unlikely(!(likely(tp_self->tp_seq && tp_self->tp_seq->tp_foreach) ||
+	              unlikely(DeeType_InheritIter(tp_self)))) {
+		err_unimplemented_operator(tp_self, OPERATOR_ITER);
+		goto err;
+	}
+
+	data.sahvd_vector = *p_vector;
+#ifdef Dee_MallocUsableSize
+	data.sahvd_alloc = Dee_MallocUsableSize(data.sahvd_vector) / sizeof(DREF DeeObject *);
+#else /* Dee_MallocUsableSize */
+	data.sahvd_alloc = *p_allocated;
+#endif /* !Dee_MallocUsableSize */
+	ASSERT(data.sahvd_alloc >= offset);
+	ASSERT(!data.sahvd_alloc || data.sahvd_vector);
+
+	/* Try to use "tp_size_fast" to get a good guess regarding the initial buffer size. */
+	if likely(tp_self->tp_seq->tp_size_fast) {
+		size_t min_alloc;
+		min_alloc = (*tp_self->tp_seq->tp_size_fast)(self);
+		if (min_alloc != (size_t)-1 && !OVERFLOW_UADD(min_alloc, offset, &min_alloc)) {
+			if (min_alloc > data.sahvd_alloc) {
+				DREF DeeObject **new_vector;
+				new_vector = (DREF DeeObject **)Dee_TryReallocc(data.sahvd_vector, min_alloc,
+				                                                sizeof(DREF DeeObject *));
+				if likely(new_vector) {
+					data.sahvd_vector = new_vector;
+					data.sahvd_alloc  = min_alloc;
+				}
+			}
+		}
+	}
+
+	/* Check if the type supports the "tp_asvector" extension. */
+	if (tp_self->tp_seq->tp_asvector) {
+		DREF DeeObject **new_vector;
+again_asvector:
+		data.sahvd_size = (*tp_self->tp_seq->tp_asvector)(self,
+		                                                  data.sahvd_vector + offset,
+		                                                  data.sahvd_alloc - offset);
+		if likely(data.sahvd_size <= (data.sahvd_alloc - offset)) {
+			data.sahvd_size += offset;
+			goto done;
+		}
+		if unlikely(data.sahvd_size == (size_t)-1) {
+			data.sahvd_size += offset;
+			goto done;
+		}
+		/* Need a larger vector buffer. */
+		if unlikely(OVERFLOW_UADD(data.sahvd_size, offset, &data.sahvd_alloc)) {
+			Dee_BadAlloc((size_t)-1);
+			goto err_writeback;
+		}
+		new_vector = (DREF DeeObject **)Dee_Reallocc(data.sahvd_vector,
+		                                             data.sahvd_alloc,
+		                                             sizeof(DREF DeeObject *));
+		if unlikely(!new_vector)
+			goto err_writeback;
+		data.sahvd_vector = new_vector;
+		goto again_asvector;
+	}
+
+	/* Use `DeeObject_Foreach()' */
+	data.sahvd_size = offset;
+	ASSERT(data.sahvd_size <= data.sahvd_alloc);
+	if unlikely((*tp_self->tp_seq->tp_foreach)(self, &foreach_seq_as_heap_vector_cb, &data))
+		goto err_writeback_data;
+	ASSERT(data.sahvd_size <= data.sahvd_alloc);
+	ASSERT(data.sahvd_size >= offset);
+
+done:
+	*p_vector = data.sahvd_vector;
+#ifndef Dee_MallocUsableSize
+	*p_allocated = data.sahvd_alloc;
+#endif /* !Dee_MallocUsableSize */
+	return data.sahvd_size - offset;
+err_writeback_data:
+	Dee_Decrefv(data.sahvd_vector + offset,
+	            data.sahvd_size - offset);
+err_writeback:
+	data.sahvd_size = (size_t)-1;
+	goto done;
+err:
+	return (size_t)-1;
+#else /* CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 	Dee_ssize_t error;
 	struct foreach_seq_as_heap_vector_data data;
 	data.sahvd_vector = *p_vector;
@@ -640,6 +945,7 @@ DeeSeq_AsHeapVectorWithAllocReuseOffset(DeeObject *__restrict self,
 	            data.sahvd_size - offset);
 err:
 	return (size_t)-1;
+#endif /* !CONFIG_EXPERIMENTAL_NEW_SEQUENCE_OPERATORS */
 }
 
 
diff --git a/src/deemon/objects/seq/repeat.c b/src/deemon/objects/seq/repeat.c
index 9d906843..98a5a450 100644
--- a/src/deemon/objects/seq/repeat.c
+++ b/src/deemon/objects/seq/repeat.c
@@ -1013,6 +1013,17 @@ repeatitem_foreach_pair(RepeatItem *self, Dee_foreach_pair_t proc, void *arg) {
 	return -1;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+repeatitem_asvector(RepeatItem *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	if unlikely(self->rpit_num == (size_t)-1) {
+		err_integer_overflow_i(sizeof(size_t) * 8, true);
+	} else {
+		if likely(dst_length >= self->rpit_num)
+			Dee_Setrefv(dst, self->rpit_obj, self->rpit_num);
+	}
+	return self->rpit_num;
+}
+
 
 PRIVATE struct type_nsi tpconst repeatitem_nsi = {
 	/* .nsi_class   = */ TYPE_SEQX_CLASS_SEQ,
@@ -1077,6 +1088,7 @@ PRIVATE struct type_seq repeatitem_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&repeatitem_asvector,
 };
 
 PRIVATE struct type_member tpconst repeatitem_members[] = {
diff --git a/src/deemon/objects/seq/svec.c b/src/deemon/objects/seq/svec.c
index 22475d86..8e9385b8 100644
--- a/src/deemon/objects/seq/svec.c
+++ b/src/deemon/objects/seq/svec.c
@@ -1097,6 +1097,17 @@ svec_enumerate_index(SharedVector *self, Dee_enumerate_index_t proc,
 	return temp;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+svec_asvector(SharedVector *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	size_t realsize;
+	SharedVector_LockRead(self);
+	realsize = self->sv_length;
+	if likely(dst_length >= realsize)
+		Dee_Movrefv(dst, self->sv_vector, realsize);
+	SharedVector_LockEndRead(self);
+	return realsize;
+}
+
 
 PRIVATE struct type_nsi tpconst svec_nsi = {
 	/* .nsi_class   = */ TYPE_SEQX_CLASS_SEQ,
@@ -1322,6 +1333,7 @@ PRIVATE struct type_seq svec_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&svec_asvector,
 };
 
 PRIVATE struct type_getset tpconst svec_getsets[] = {
diff --git a/src/deemon/objects/string.c b/src/deemon/objects/string.c
index d06bc342..bbcc198f 100644
--- a/src/deemon/objects/string.c
+++ b/src/deemon/objects/string.c
@@ -1610,6 +1610,69 @@ string_foreach(String *self, Dee_foreach_t proc, void *arg) {
 	return -1;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+string_asvector(String *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	size_t result;
+	union dcharptr ptr, end;
+	DREF DeeObject **dst_iter = dst;
+	SWITCH_SIZEOF_WIDTH(DeeString_WIDTH(self)) {
+
+	CASE_WIDTH_1BYTE:
+		ptr.cp8 = DeeString_Get1Byte((DeeObject *)self);
+		result  = WSTR_LENGTH(ptr.cp8);
+		if unlikely(dst_length < result)
+			break;
+		end.cp8 = ptr.cp8 + result;
+		for (; ptr.cp8 < end.cp8; ++ptr.cp8) {
+			DREF DeeObject *chr;
+#ifdef CONFIG_STRING_LATIN1_STATIC
+			chr = (DeeObject *)&DeeString_Latin1[*ptr.cp8];
+			Dee_Incref(chr);
+#else /* CONFIG_STRING_LATIN1_STATIC */
+			chr = DeeString_Chr(*ptr.cp8);
+			if unlikely(!chr)
+				goto err_dst_iter;
+#endif /* !CONFIG_STRING_LATIN1_STATIC */
+			*dst_iter++ = chr;
+		}
+		break;
+
+	CASE_WIDTH_2BYTE:
+		ptr.cp16 = DeeString_Get2Byte((DeeObject *)self);
+		result   = WSTR_LENGTH(ptr.cp16);
+		if unlikely(dst_length < result)
+			break;
+		end.cp16 = ptr.cp16 + result;
+		for (; ptr.cp16 < end.cp16; ++ptr.cp16) {
+			DREF DeeObject *chr;
+			chr = DeeString_Chr(*ptr.cp16);
+			if unlikely(!chr)
+				goto err_dst_iter;
+			*dst_iter++ = chr;
+		}
+		break;
+
+	CASE_WIDTH_4BYTE:
+		ptr.cp32 = DeeString_Get4Byte((DeeObject *)self);
+		result   = WSTR_LENGTH(ptr.cp32);
+		if unlikely(dst_length < result)
+			break;
+		end.cp32 = ptr.cp32 + result;
+		for (; ptr.cp32 < end.cp32; ++ptr.cp32) {
+			DREF DeeObject *chr;
+			chr = DeeString_Chr(*ptr.cp32);
+			if unlikely(!chr)
+				goto err_dst_iter;
+			*dst_iter++ = chr;
+		}
+		break;
+	}
+	return result;
+err_dst_iter:
+	Dee_Decrefv(dst, (size_t)(dst_iter - dst));
+	return (size_t)-1;
+}
+
 PRIVATE struct type_nsi tpconst string_nsi = {
 	/* .nsi_class   = */ TYPE_SEQX_CLASS_SEQ,
 	/* .nsi_flags   = */ TYPE_SEQX_FNORMAL,
@@ -1673,6 +1736,7 @@ PRIVATE struct type_seq string_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&string_asvector,
 };
 
 PRIVATE struct type_member tpconst string_class_members[] = {
diff --git a/src/deemon/objects/tuple.c b/src/deemon/objects/tuple.c
index 4de033c1..44895957 100644
--- a/src/deemon/objects/tuple.c
+++ b/src/deemon/objects/tuple.c
@@ -1581,6 +1581,14 @@ tuple_enumerate_index(Tuple *self, Dee_enumerate_index_t proc,
 	return temp;
 }
 
+PRIVATE WUNUSED NONNULL((1)) size_t DCALL
+tuple_asvector(Tuple *self, /*out*/ DREF DeeObject **dst, size_t dst_length) {
+	if unlikely(dst_length < self->t_size)
+		return self->t_size;
+	Dee_Movrefv(dst, self->t_elem, self->t_size);
+	return self->t_size;
+}
+
 PRIVATE struct type_nsi tpconst tuple_nsi = {
 	/* .nsi_class   = */ TYPE_SEQX_CLASS_SEQ,
 	/* .nsi_flags   = */ TYPE_SEQX_FNORMAL,
@@ -1645,6 +1653,7 @@ PRIVATE struct type_seq tuple_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ NULL,
+	/* .tp_asvector                   = */ (size_t (DCALL *)(DeeObject *, DREF DeeObject **, size_t))&tuple_asvector,
 };
 
 PRIVATE WUNUSED NONNULL((1)) DREF Tuple *DCALL
diff --git a/src/deemon/runtime/kwds-wrappers.c b/src/deemon/runtime/kwds-wrappers.c
index 8736efbf..c7e6e35e 100644
--- a/src/deemon/runtime/kwds-wrappers.c
+++ b/src/deemon/runtime/kwds-wrappers.c
@@ -817,6 +817,7 @@ PRIVATE struct type_seq blv_seq = {
 	/* .tp_setitem_string_len_hash      = */ NULL,
 	/* .tp_bounditem_string_len_hash    = */ NULL,
 	/* .tp_hasitem_string_len_hash      = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&blv_hasitem_string_len_hash,
+	/* .tp_asvector                     = */ NULL,
 	/* .tp_getitemnr                    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, /*string*/ DeeObject *__restrict))&blv_getitemnr,
 	/* .tp_getitemnr_string_hash        = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, Dee_hash_t))&blv_getitemnr_string_hash,
 	/* .tp_getitemnr_string_len_hash    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, size_t, Dee_hash_t))&blv_getitemnr_string_len_hash,
@@ -1817,6 +1818,7 @@ PRIVATE struct type_seq blkw_seq = {
 	/* .tp_setitem_string_len_hash      = */ NULL,
 	/* .tp_bounditem_string_len_hash    = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&blkw_bounditem_string_len_hash,
 	/* .tp_hasitem_string_len_hash      = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&blkw_hasitem_string_len_hash,
+	/* .tp_asvector                     = */ NULL,
 	/* .tp_getitemnr                    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, /*string*/ DeeObject *__restrict))&blkw_getitemnr,
 	/* .tp_getitemnr_string_hash        = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, Dee_hash_t))&blkw_getitemnr_string_hash,
 	/* .tp_getitemnr_string_len_hash    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, size_t, Dee_hash_t))&blkw_getitemnr_string_len_hash,
diff --git a/src/deemon/runtime/kwds.c b/src/deemon/runtime/kwds.c
index 84a1485e..455feaa8 100644
--- a/src/deemon/runtime/kwds.c
+++ b/src/deemon/runtime/kwds.c
@@ -1526,6 +1526,7 @@ PRIVATE struct type_seq kmap_seq = {
 	/* .tp_setitem_string_len_hash    = */ NULL,
 	/* .tp_bounditem_string_len_hash  = */ NULL,
 	/* .tp_hasitem_string_len_hash    = */ (int (DCALL *)(DeeObject *, char const *, size_t, Dee_hash_t))&kmap_hasitem_string_len_hash,
+	/* .tp_asvector                     = */ NULL,
 	/* .tp_getitemnr                    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, /*string*/ DeeObject *__restrict))&kmap_getitemnr,
 	/* .tp_getitemnr_string_hash        = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, Dee_hash_t))&kmap_getitemnr_string_hash,
 	/* .tp_getitemnr_string_len_hash    = */ (DeeObject *(DCALL *)(DeeObject *__restrict, char const *__restrict, size_t, Dee_hash_t))&kmap_getitemnr_string_len_hash,
diff --git a/src/deemon/runtime/operator.c b/src/deemon/runtime/operator.c
index a072fd2e..8f174dc5 100644
--- a/src/deemon/runtime/operator.c
+++ b/src/deemon/runtime/operator.c
@@ -16517,6 +16517,7 @@ DeeType_InheritSeqOperators(DeeTypeObject *__restrict self, unsigned int seqclas
 			self->tp_seq->tp_setitem_string_len_hash    = base_seq->tp_setitem_string_len_hash;
 			self->tp_seq->tp_bounditem_string_len_hash  = base_seq->tp_bounditem_string_len_hash;
 			self->tp_seq->tp_hasitem_string_len_hash    = base_seq->tp_hasitem_string_len_hash;
+			self->tp_seq->tp_asvector                   = base_seq->tp_asvector;
 		} else {
 			self->tp_seq = base_seq;
 		}
@@ -16589,6 +16590,7 @@ DeeType_InheritIter(DeeTypeObject *__restrict self) {
 			self->tp_seq->tp_iter         = base_seq->tp_iter;
 			self->tp_seq->tp_foreach      = base_seq->tp_foreach;
 			self->tp_seq->tp_foreach_pair = base_seq->tp_foreach_pair;
+			self->tp_seq->tp_asvector     = base_seq->tp_asvector;
 		} else {
 			self->tp_seq = base_seq;
 		}