diff --git a/benchmark/napi/function_args/binding.cc b/benchmark/napi/function_args/binding.cc
index 078fe0ee3ea..5cdca8bd357 100644
--- a/benchmark/napi/function_args/binding.cc
+++ b/benchmark/napi/function_args/binding.cc
@@ -21,9 +21,10 @@ void CallWithString(const FunctionCallbackInfo<Value>& args) {
   assert(args.Length() == 1 && args[0]->IsString());
   if (args.Length() == 1 && args[0]->IsString()) {
     Local<String> str = args[0].As<String>();
-    const int32_t length = str->Utf8Length(args.GetIsolate()) + 1;
+    const size_t length = str->Utf8LengthV2(args.GetIsolate()) + 1;
     char* buf = new char[length];
-    str->WriteUtf8(args.GetIsolate(), buf, length);
+    str->WriteUtf8V2(
+        args.GetIsolate(), buf, length, String::WriteFlags::kNullTerminate);
     delete[] buf;
   }
 }
diff --git a/src/crypto/crypto_util.cc b/src/crypto/crypto_util.cc
index 60610b1b795..0745304d379 100644
--- a/src/crypto/crypto_util.cc
+++ b/src/crypto/crypto_util.cc
@@ -393,12 +393,12 @@ ByteSource ByteSource::FromStringOrBuffer(Environment* env,
 ByteSource ByteSource::FromString(Environment* env, Local<String> str,
                                   bool ntc) {
   CHECK(str->IsString());
-  size_t size = str->Utf8Length(env->isolate());
+  size_t size = str->Utf8LengthV2(env->isolate());
   size_t alloc_size = ntc ? size + 1 : size;
   ByteSource::Builder out(alloc_size);
-  int opts = String::NO_OPTIONS;
-  if (!ntc) opts |= String::NO_NULL_TERMINATION;
-  str->WriteUtf8(env->isolate(), out.data<char>(), alloc_size, nullptr, opts);
+  int opts = String::WriteFlags::kNone;
+  if (ntc) opts |= String::WriteFlags::kNullTerminate;
+  str->WriteUtf8V2(env->isolate(), out.data<char>(), alloc_size, opts);
   return std::move(out).release();
 }
 
diff --git a/src/encoding_binding.cc b/src/encoding_binding.cc
index 885a0d07231..0d2941cef16 100644
--- a/src/encoding_binding.cc
+++ b/src/encoding_binding.cc
@@ -100,6 +100,7 @@ void BindingData::EncodeInto(const FunctionCallbackInfo<Value>& args) {
   size_t dest_length = dest->ByteLength();
 
   int nchars;
+  // TODO: Use `WriteUtf8V2`, which has no `nchars_ref` parameter.
   int written = source->WriteUtf8(
       isolate,
       write_result,
@@ -120,7 +121,7 @@ void BindingData::EncodeUtf8String(const FunctionCallbackInfo<Value>& args) {
   CHECK(args[0]->IsString());
 
   Local<String> str = args[0].As<String>();
-  size_t length = str->Utf8Length(isolate);
+  size_t length = str->Utf8LengthV2(isolate);
 
   Local<ArrayBuffer> ab;
   {
@@ -130,11 +131,11 @@ void BindingData::EncodeUtf8String(const FunctionCallbackInfo<Value>& args) {
 
     CHECK(bs);
 
-    str->WriteUtf8(isolate,
-                   static_cast<char*>(bs->Data()),
-                   -1,  // We are certain that `data` is sufficiently large
-                   nullptr,
-                   String::NO_NULL_TERMINATION | String::REPLACE_INVALID_UTF8);
+    str->WriteUtf8V2(
+        isolate,
+        static_cast<char*>(bs->Data()),
+        length,  // We are certain that `data` is sufficiently large
+        String::WriteFlags::kReplaceInvalidUtf8);
 
     ab = ArrayBuffer::New(isolate, std::move(bs));
   }
diff --git a/src/js_native_api_v8.cc b/src/js_native_api_v8.cc
index 6e1680a74e2..abb4f8d6ff4 100644
--- a/src/js_native_api_v8.cc
+++ b/src/js_native_api_v8.cc
@@ -2446,16 +2446,13 @@ napi_status NAPI_CDECL napi_get_value_string_latin1(
     CHECK_ARG(env, result);
     *result = val.As<v8::String>()->Length();
   } else if (bufsize != 0) {
-    int copied =
-        val.As<v8::String>()->WriteOneByte(env->isolate,
-                                           reinterpret_cast<uint8_t*>(buf),
-                                           0,
-                                           bufsize - 1,
-                                           v8::String::NO_NULL_TERMINATION);
+    size_t length = bufsize - 1;
+    val.As<v8::String>()->WriteOneByteV2(
+        env->isolate, 0, length, reinterpret_cast<uint8_t*>(buf));
 
-    buf[copied] = '\0';
+    buf[length] = '\0';
     if (result != nullptr) {
-      *result = copied;
+      *result = length;
     }
   } else if (result != nullptr) {
     *result = 0;
@@ -2482,14 +2479,13 @@ napi_status NAPI_CDECL napi_get_value_string_utf8(
 
   if (!buf) {
     CHECK_ARG(env, result);
-    *result = val.As<v8::String>()->Utf8Length(env->isolate);
+    *result = val.As<v8::String>()->Utf8LengthV2(env->isolate);
   } else if (bufsize != 0) {
-    int copied = val.As<v8::String>()->WriteUtf8(
+    size_t copied = val.As<v8::String>()->WriteUtf8V2(
         env->isolate,
         buf,
         bufsize - 1,
-        nullptr,
-        v8::String::REPLACE_INVALID_UTF8 | v8::String::NO_NULL_TERMINATION);
+        v8::String::WriteFlags::kReplaceInvalidUtf8);
 
     buf[copied] = '\0';
     if (result != nullptr) {
@@ -2526,15 +2522,13 @@ napi_status NAPI_CDECL napi_get_value_string_utf16(napi_env env,
     // V8 assumes UTF-16 length is the same as the number of characters.
     *result = val.As<v8::String>()->Length();
   } else if (bufsize != 0) {
-    int copied = val.As<v8::String>()->Write(env->isolate,
-                                             reinterpret_cast<uint16_t*>(buf),
-                                             0,
-                                             bufsize - 1,
-                                             v8::String::NO_NULL_TERMINATION);
+    size_t length = bufsize - 1;
+    val.As<v8::String>()->WriteV2(
+        env->isolate, 0, length, reinterpret_cast<uint16_t*>(buf));
 
-    buf[copied] = '\0';
+    buf[length] = '\0';
     if (result != nullptr) {
-      *result = copied;
+      *result = length;
     }
   } else if (result != nullptr) {
     *result = 0;
diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index 8e659ac06ab..40e82031741 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -650,7 +650,7 @@ void Fill(const FunctionCallbackInfo<Value>& args) {
   // Can't use StringBytes::Write() in all cases. For example if attempting
   // to write a two byte character into a one byte Buffer.
   if (enc == UTF8) {
-    str_length = str_obj->Utf8Length(env->isolate());
+    str_length = str_obj->Utf8LengthV2(env->isolate());
     node::Utf8Value str(env->isolate(), args[1]);
     memcpy(ts_obj_data + start, *str, std::min(str_length, fill_length));
 
@@ -736,7 +736,8 @@ void SlowByteLengthUtf8(const FunctionCallbackInfo<Value>& args) {
   CHECK(args[0]->IsString());
 
   // Fast case: avoid StringBytes on UTF8 string. Jump to v8.
-  args.GetReturnValue().Set(args[0].As<String>()->Utf8Length(env->isolate()));
+  size_t length = args[0].As<String>()->Utf8LengthV2(env->isolate());
+  args.GetReturnValue().Set(static_cast<uint64_t>(length));
 }
 
 uint32_t FastByteLengthUtf8(Local<Value> receiver,
@@ -1003,8 +1004,7 @@ void IndexOfString(const FunctionCallbackInfo<Value>& args) {
     if (needle_data == nullptr) {
       return args.GetReturnValue().Set(-1);
     }
-    needle->WriteOneByte(
-        isolate, needle_data, 0, needle_length, String::NO_NULL_TERMINATION);
+    needle->WriteOneByteV2(isolate, 0, needle_length, needle_data);
 
     result = nbytes::SearchString(reinterpret_cast<const uint8_t*>(haystack),
                                   haystack_length,
@@ -1254,11 +1254,7 @@ static void Btoa(const FunctionCallbackInfo<Value>& args) {
         simdutf::binary_to_base64(ext->data(), ext->length(), buffer.out());
   } else if (input->IsOneByte()) {
     MaybeStackBuffer<uint8_t> stack_buf(input->Length());
-    input->WriteOneByte(env->isolate(),
-                        stack_buf.out(),
-                        0,
-                        input->Length(),
-                        String::NO_NULL_TERMINATION);
+    input->WriteOneByteV2(env->isolate(), 0, input->Length(), stack_buf.out());
 
     size_t expected_length =
         simdutf::base64_length_from_binary(input->Length());
@@ -1317,11 +1313,8 @@ static void Atob(const FunctionCallbackInfo<Value>& args) {
         ext->data(), ext->length(), buffer.out(), simdutf::base64_default);
   } else if (input->IsOneByte()) {
     MaybeStackBuffer<uint8_t> stack_buf(input->Length());
-    input->WriteOneByte(args.GetIsolate(),
-                        stack_buf.out(),
-                        0,
-                        input->Length(),
-                        String::NO_NULL_TERMINATION);
+    input->WriteOneByteV2(
+        args.GetIsolate(), 0, input->Length(), stack_buf.out());
     const char* data = reinterpret_cast<const char*>(*stack_buf);
     size_t expected_length =
         simdutf::maximal_binary_length_from_base64(data, input->Length());
diff --git a/src/node_http2.cc b/src/node_http2.cc
index b23f4080a6d..3f0b25b3435 100644
--- a/src/node_http2.cc
+++ b/src/node_http2.cc
@@ -474,13 +474,10 @@ Origins::Origins(
 
   CHECK_LE(origin_contents + origin_string_len,
            static_cast<char*>(bs_->Data()) + bs_->ByteLength());
-  CHECK_EQ(origin_string->WriteOneByte(
-               env->isolate(),
-               reinterpret_cast<uint8_t*>(origin_contents),
-               0,
-               origin_string_len,
-               String::NO_NULL_TERMINATION),
-           origin_string_len);
+  origin_string->WriteOneByteV2(env->isolate(),
+                                0,
+                                origin_string_len,
+                                reinterpret_cast<uint8_t*>(origin_contents));
 
   size_t n = 0;
   char* p;
@@ -3129,8 +3126,13 @@ void Http2Session::AltSvc(const FunctionCallbackInfo<Value>& args) {
 
   MaybeStackBuffer<uint8_t> origin(origin_len);
   MaybeStackBuffer<uint8_t> value(value_len);
-  origin_str->WriteOneByte(env->isolate(), *origin);
-  value_str->WriteOneByte(env->isolate(), *value);
+  origin_str->WriteOneByteV2(env->isolate(),
+                             0,
+                             origin_len,
+                             *origin,
+                             String::WriteFlags::kNullTerminate);
+  value_str->WriteOneByteV2(
+      env->isolate(), 0, value_len, *value, String::WriteFlags::kNullTerminate);
 
   session->AltSvc(id, *origin, origin_len, *value, value_len);
 }
diff --git a/src/node_http_common-inl.h b/src/node_http_common-inl.h
index f7f4408ecb6..8eb4fe8aa6f 100644
--- a/src/node_http_common-inl.h
+++ b/src/node_http_common-inl.h
@@ -37,13 +37,11 @@ NgHeaders<T>::NgHeaders(Environment* env, v8::Local<v8::Array> headers) {
   nv_t* const nva = reinterpret_cast<nv_t*>(start);
 
   CHECK_LE(header_contents + header_string_len, *buf_ + buf_.length());
-  CHECK_EQ(header_string.As<v8::String>()->WriteOneByte(
+  header_string.As<v8::String>()->WriteOneByteV2(
                env->isolate(),
-               reinterpret_cast<uint8_t*>(header_contents),
                0,
                header_string_len,
-               v8::String::NO_NULL_TERMINATION),
-           header_string_len);
+               reinterpret_cast<uint8_t*>(header_contents));
 
   size_t n = 0;
   char* p;
diff --git a/src/string_bytes.cc b/src/string_bytes.cc
index 8a94d0eb632..f2b900a638f 100644
--- a/src/string_bytes.cc
+++ b/src/string_bytes.cc
@@ -200,8 +200,11 @@ MaybeLocal<Value> ExternTwoByteString::NewSimpleFromCopy(Isolate* isolate,
 
 }  // anonymous namespace
 
-size_t StringBytes::WriteUCS2(
-    Isolate* isolate, char* buf, size_t buflen, Local<String> str, int flags) {
+size_t StringBytes::WriteUCS2(Isolate* isolate,
+                              char* buf,
+                              size_t buflen,
+                              Local<String> str,
+                              int flags = String::WriteFlags::kNone) {
   uint16_t* const dst = reinterpret_cast<uint16_t*>(buf);
 
   size_t max_chars = buflen / sizeof(*dst);
@@ -212,7 +215,8 @@ size_t StringBytes::WriteUCS2(
   uint16_t* const aligned_dst = nbytes::AlignUp(dst, sizeof(*dst));
   size_t nchars;
   if (aligned_dst == dst) {
-    nchars = str->Write(isolate, dst, 0, max_chars, flags);
+    nchars = max_chars;
+    str->WriteV2(isolate, 0, nchars, dst, flags);
     return nchars * sizeof(*dst);
   }
 
@@ -223,15 +227,15 @@ size_t StringBytes::WriteUCS2(
   if (max_chars == 0) {
     return 0;
   }
-  nchars = str->Write(isolate, aligned_dst, 0, max_chars - 1, flags);
-  CHECK_EQ(nchars, max_chars - 1);
+  nchars = max_chars - 1;
+  str->WriteV2(isolate, 0, nchars, aligned_dst, flags);
 
   // Shift everything to unaligned-left
   memmove(dst, aligned_dst, nchars * sizeof(*dst));
 
   // One more char to be written
   uint16_t last;
-  CHECK_EQ(str->Write(isolate, &last, nchars, 1, flags), 1);
+  str->WriteV2(isolate, nchars, 1, &last, flags);
   memcpy(buf + nchars * sizeof(*dst), &last, sizeof(last));
   nchars++;
 
@@ -250,9 +254,7 @@ size_t StringBytes::Write(Isolate* isolate,
   Local<String> str = val.As<String>();
   String::ValueView input_view(isolate, str);
 
-  int flags = String::HINT_MANY_WRITES_EXPECTED |
-              String::NO_NULL_TERMINATION |
-              String::REPLACE_INVALID_UTF8;
+  int flags = String::WriteFlags::kReplaceInvalidUtf8;
 
   switch (encoding) {
     case ASCII:
@@ -262,13 +264,14 @@ size_t StringBytes::Write(Isolate* isolate,
         memcpy(buf, input_view.data8(), nbytes);
       } else {
         uint8_t* const dst = reinterpret_cast<uint8_t*>(buf);
-        nbytes = str->WriteOneByte(isolate, dst, 0, buflen, flags);
+        str->WriteOneByteV2(isolate, 0, buflen, dst, flags);
+        nbytes = buflen;
       }
       break;
 
     case BUFFER:
     case UTF8:
-      nbytes = str->WriteUtf8(isolate, buf, buflen, nullptr, flags);
+      nbytes = str->WriteUtf8V2(isolate, buf, buflen, flags);
       break;
 
     case UCS2: {
diff --git a/src/util.cc b/src/util.cc
index 8bf239db6e4..ee912792a03 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -127,10 +127,9 @@ static void MakeUtf8String(Isolate* isolate,
 
   // TODO(@anonrig): Use simdutf to speed up non-one-byte strings once it's
   // implemented
-  const int flags =
-      String::NO_NULL_TERMINATION | String::REPLACE_INVALID_UTF8;
-  const int length =
-      string->WriteUtf8(isolate, target->out(), storage, nullptr, flags);
+  const int flags = String::WriteFlags::kReplaceInvalidUtf8;
+  const size_t length =
+      string->WriteUtf8V2(isolate, target->out(), storage, flags);
   target->SetLengthAndZeroTerminate(length);
 }
 
@@ -154,9 +153,8 @@ TwoByteValue::TwoByteValue(Isolate* isolate, Local<Value> value) {
   const size_t storage = string->Length() + 1;
   AllocateSufficientStorage(storage);
 
-  const int flags = String::NO_NULL_TERMINATION;
-  const int length = string->Write(isolate, out(), 0, storage, flags);
-  SetLengthAndZeroTerminate(length);
+  string->WriteV2(isolate, 0, storage - 1, out());
+  SetLengthAndZeroTerminate(storage);
 }
 
 BufferValue::BufferValue(Isolate* isolate, Local<Value> value) {