nemotron : support non-standard GQA, BPE tokenizer and domyn-small pre-type (#23343)

* nemotron : support non-standard GQA, BPE tokenizer and domyn-small pre-type

* gguf-py : write Metaspace prepend_scheme as GGUF metadata

* vocab : parse metaspace prepend_scheme into enum, rename key

* vocab : use metaspace prepend_scheme in detokenize, add TODOs for other tokenizers

* vocab : use constant for metaspace escaped space

---------

Co-authored-by: Martin Cimmino <martin.cimmino@domyn.com>

conversion/base.py

@@ -1837,6 +1837,9 @@ class TextModel(ModelBase):
         if chkhsh == "1431a23e583c97432bc230bff598d103ddb5a1f89960c8f1d1051aaa944d0b35":
             # ref: https://huggingface.co/sapienzanlp/Minerva-7B-base-v1.0
             res = "minerva-7b"
+        if chkhsh == "6e4d72c6e5260b90606e26a0931fa15e4b42ec6e97719d12919f2b1f93478262":
+            # ref: https://huggingface.co/domyn/Domyn-Small-v1.0
+            res = "domyn-small"
         if chkhsh == "7e57df22b1fe23a7b1e1c7f3dc4e3f96d43a4eb0836d0c6bdc3436d7b2f1c664":
             # ref: https://huggingface.co/tencent/Hunyuan-A13B-Instruct
             res = "hunyuan"

conversion/nemotron.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import re
 from typing import Any, Callable, Iterable, Sequence, TYPE_CHECKING
 
 import numpy as np
@@ -367,9 +368,21 @@ class NemotronModel(TextModel):
     model_arch = gguf.MODEL_ARCH.NEMOTRON
 
     def set_vocab(self):
-        self._set_vocab_sentencepiece()
+        if (self.dir_model / "tokenizer.model").exists():
-        self.gguf_writer.add_pad_token_id(0)
+            self._set_vocab_sentencepiece()
-        self.gguf_writer.add_unk_token_id(1)
+            self.gguf_writer.add_pad_token_id(0)
+            self.gguf_writer.add_unk_token_id(1)
+        else:
+            # SPM-style BPE (Metaspace + byte fallback): mark <0xXX> tokens as BYTE so they decode to raw bytes
+            tokens, toktypes, tokpre = self.get_vocab_base()
+            toktypes = [gguf.TokenType.BYTE if re.fullmatch(r"<0x[0-9A-F]{2}>", tok) else typ for tok, typ in zip(tokens, toktypes)]
+            self.gguf_writer.add_tokenizer_model("gpt2")
+            self.gguf_writer.add_tokenizer_pre(tokpre)
+            self.gguf_writer.add_token_list(tokens)
+            self.gguf_writer.add_token_types(toktypes)
+
+            special_vocab = gguf.SpecialVocab(self.dir_model, load_merges=True)
+            special_vocab.add_to_gguf(self.gguf_writer)
 
     def set_gguf_parameters(self):
         super().set_gguf_parameters()
@@ -383,7 +396,10 @@ class NemotronModel(TextModel):
         rot_pct = self.rope_parameters["partial_rotary_factor"]
         n_embd = self.find_hparam(["hidden_size", "n_embd"])
         n_head = self.find_hparam(["num_attention_heads", "n_head"])
-        self.gguf_writer.add_rope_dimension_count(int(rot_pct * n_embd) // n_head)
+        # Use explicit head_dim when available; fallback keeps standard Nemotron working.
+        # Without this, models where n_head * head_dim != n_embd (e.g. 48 heads, head_dim=128) produce the wrong rope dimension count.
+        head_dim = self.hparams.get("head_dim") or n_embd // n_head
+        self.gguf_writer.add_rope_dimension_count(int(rot_pct * head_dim))
 
         # * RopeScaling for Nemotron
         factor = self.hparams.get("factor") or self.rope_parameters.get("factor")

convert_hf_to_gguf_update.py

@@ -178,6 +178,7 @@ pre_computed_hashes = [
     {"name": "glm4", "tokt": TOKENIZER_TYPE.BPE, "repo": "https://huggingface.co/zai-org/GLM-4.5-Air", "chkhsh": "9ca2dd618e8afaf09731a7cf6e2105b373ba6a1821559f258b272fe83e6eb902"},
     {"name": "glm4", "tokt": TOKENIZER_TYPE.BPE, "repo": "https://huggingface.co/zai-org/GLM-4.7-Flash", "chkhsh": "cdf5f35325780597efd76153d4d1c16778f766173908894c04afc20108536267"},
     {"name": "minerva-7b", "tokt": TOKENIZER_TYPE.BPE, "repo": "https://huggingface.co/sapienzanlp/Minerva-7B-base-v1.0", "chkhsh": "1431a23e583c97432bc230bff598d103ddb5a1f89960c8f1d1051aaa944d0b35"},
+    {"name": "domyn-small", "tokt": TOKENIZER_TYPE.BPE, "repo": "https://huggingface.co/domyn/Domyn-Small-v1.0", "chkhsh": "6e4d72c6e5260b90606e26a0931fa15e4b42ec6e97719d12919f2b1f93478262"},
     {"name": "hunyuan", "tokt": TOKENIZER_TYPE.BPE, "repo": "https://huggingface.co/tencent/Hunyuan-A13B-Instruct", "chkhsh": "7e57df22b1fe23a7b1e1c7f3dc4e3f96d43a4eb0836d0c6bdc3436d7b2f1c664"},
     {"name": "hunyuan-dense", "tokt": TOKENIZER_TYPE.BPE, "repo": "https://huggingface.co/tencent/Hunyuan-4B-Instruct", "chkhsh": "bba3b3366b646dbdded5dbc42d59598b849371afc42f7beafa914afaa5b70aa6"},
     {"name": "hy_v4", "tokt": TOKENIZER_TYPE.BPE, "repo": "https://huggingface.co/tencent/Hy4-preview", "chkhsh": "e6ddf9c6686791c12d698d34c31ab9be1fea9af5a3d9a6909783ab382198ae1c"},

gguf-py/gguf/constants.py

@@ -383,6 +383,8 @@ class Keys:
         NORMALIZER_NFC           = "tokenizer.ggml.normalizer.nfc"
         NORMALIZER_LOWERCASE     = "tokenizer.ggml.normalizer.lowercase"
         NORMALIZER_STRIP_ACCENTS = "tokenizer.ggml.normalizer.strip_accents"
+        # Metaspace constants
+        METASPACE_PREPEND_SCHEME = "tokenizer.ggml.metaspace.prepend_scheme"
         # FIM/Infill special tokens constants
         FIM_PRE_ID           = "tokenizer.ggml.fim_pre_token_id"
         FIM_SUF_ID           = "tokenizer.ggml.fim_suf_token_id"

gguf-py/gguf/gguf_writer.py

@@ -1377,6 +1377,9 @@ class GGUFWriter:
     def add_normalizer_strip_accents(self, value: bool) -> None:
         self.add_bool(Keys.Tokenizer.NORMALIZER_STRIP_ACCENTS, value)
 
+    def add_metaspace_prepend_scheme(self, value: str) -> None:
+        self.add_string(Keys.Tokenizer.METASPACE_PREPEND_SCHEME, value)
+
     def add_eot_token_id(self, id: int) -> None:
         self.add_uint32(Keys.Tokenizer.EOT_ID, id)
 

gguf-py/gguf/vocab.py

@@ -56,6 +56,7 @@ class SpecialVocab:
     normalizer_lowercase: bool | None
     normalizer_strip_accents: bool | None
     clean_spaces: bool | None
+    metaspace_prepend_scheme: str | None
 
     def __init__(
         self, path: str | os.PathLike[str], load_merges: bool = False,
@@ -72,6 +73,7 @@ class SpecialVocab:
         self.normalizer_lowercase = None
         self.normalizer_strip_accents = None
         self.clean_spaces = None
+        self.metaspace_prepend_scheme = None
         if special_token_types is not None:
             self.special_token_types = special_token_types
         else:
@@ -126,6 +128,10 @@ class SpecialVocab:
             if not quiet:
                 logger.info(f'Setting clean_spaces to {self.clean_spaces}')
             gw.add_clean_spaces(self.clean_spaces)
+        if self.metaspace_prepend_scheme is not None:
+            if not quiet:
+                logger.info(f'Setting metaspace_prepend_scheme to {self.metaspace_prepend_scheme}')
+            gw.add_metaspace_prepend_scheme(self.metaspace_prepend_scheme)
 
     def _load(self, path: Path) -> None:
         self._try_load_from_tokenizer_json(path)
@@ -194,6 +200,16 @@ class SpecialVocab:
             for norm in normalizer.get('normalizers', []):
                 self._parse_normalizer(norm)
 
+    def _parse_pre_tokenizer(self, pre_tokenizer: dict) -> None:
+        # ref: https://huggingface.co/docs/tokenizers/api/pre-tokenizers
+        pre_tokenizer_type = pre_tokenizer.get('type')
+        if pre_tokenizer_type == 'Metaspace':
+            if 'prepend_scheme' in pre_tokenizer:
+                self.metaspace_prepend_scheme = pre_tokenizer['prepend_scheme']
+        elif pre_tokenizer_type == 'Sequence':
+            for pre in pre_tokenizer.get('pretokenizers', []):
+                self._parse_pre_tokenizer(pre)
+
     def _try_load_from_tokenizer_json(self, path: Path) -> bool:
         tokenizer = None
         tokenizer_file = path / 'tokenizer.json'
@@ -229,6 +245,8 @@ class SpecialVocab:
             # Parse normalizer configuration (e.g. Lowercase) into metadata
             if normalizer := tokenizer.get('normalizer'):
                 self._parse_normalizer(normalizer)
+            if pre_tokenizer := tokenizer.get('pre_tokenizer'):
+                self._parse_pre_tokenizer(pre_tokenizer)
             added_tokens = tokenizer.get('added_tokens', {})
         else:
             added_tokens = {}

src/llama-arch.cpp

@@ -445,6 +445,7 @@ static const std::map<llm_kv, const char *> LLM_KV_NAMES = {
     { LLM_KV_TOKENIZER_NORMALIZER_NFC,           "tokenizer.ggml.normalizer.nfc"           },
     { LLM_KV_TOKENIZER_NORMALIZER_LOWERCASE,     "tokenizer.ggml.normalizer.lowercase"     },
     { LLM_KV_TOKENIZER_NORMALIZER_STRIP_ACCENTS, "tokenizer.ggml.normalizer.strip_accents" },
+    { LLM_KV_TOKENIZER_METASPACE_PREPEND_SCHEME, "tokenizer.ggml.metaspace.prepend_scheme" },
     { LLM_KV_TOKENIZER_FIM_PRE_ID,               "tokenizer.ggml.fim_pre_token_id"         },
     { LLM_KV_TOKENIZER_FIM_SUF_ID,               "tokenizer.ggml.fim_suf_token_id"         },
     { LLM_KV_TOKENIZER_FIM_MID_ID,               "tokenizer.ggml.fim_mid_token_id"         },

src/llama-arch.h

@@ -408,6 +408,7 @@ enum llm_kv {
     LLM_KV_TOKENIZER_NORMALIZER_NFC,
     LLM_KV_TOKENIZER_NORMALIZER_LOWERCASE,
     LLM_KV_TOKENIZER_NORMALIZER_STRIP_ACCENTS,
+    LLM_KV_TOKENIZER_METASPACE_PREPEND_SCHEME,
     LLM_KV_TOKENIZER_FIM_PRE_ID,
     LLM_KV_TOKENIZER_FIM_SUF_ID,
     LLM_KV_TOKENIZER_FIM_MID_ID,

src/llama-vocab.cpp

@@ -543,6 +543,7 @@ struct llm_tokenizer_bpe : llm_tokenizer {
                 byte_encode = false; // uses raw UTF-8, not GPT-2 byte encoding
                 break;
             case LLAMA_VOCAB_PRE_TYPE_SARVAM_MOE:
+            case LLAMA_VOCAB_PRE_TYPE_DOMYN_SMALL:
                 // Sarvam uses SPM-style BPE (same shape as Gemma4): spaces replaced with U+2581
                 // by the normalizer, BPE merges over the whole text on raw UTF-8.
                 regex_exprs = {
@@ -2097,6 +2098,8 @@ struct llama_vocab::impl {
     // Tokenizer normalizer options
     llama_vocab::normalizer_options normalizer_opts;
 
+    llama_metaspace_prepend_scheme metaspace_prepend_scheme = LLAMA_METASPACE_PREPEND_SCHEME_NEVER;
+
     std::unordered_map<std::string, llama_token> token_to_id;
     std::vector<token_data>                      id_to_token;
 
@@ -2612,6 +2615,10 @@ void llama_vocab::impl::load(llama_model_loader & ml, const LLM_KV & kv) {
             } else if (
                 tokenizer_pre == "minerva-7b") {
                 pre_type = LLAMA_VOCAB_PRE_TYPE_MINERVA;
+            } else if (
+                tokenizer_pre == "domyn-small") {
+                pre_type = LLAMA_VOCAB_PRE_TYPE_DOMYN_SMALL;
+                escape_whitespaces = true;
             } else if (
                 tokenizer_pre == "megrez") {
                 pre_type = LLAMA_VOCAB_PRE_TYPE_QWEN2;
@@ -2956,6 +2963,24 @@ void llama_vocab::impl::load(llama_model_loader & ml, const LLM_KV & kv) {
         normalizer_opts.strip_accents = normalizer_opts.lowercase;
         ml.get_key(LLM_KV_TOKENIZER_NORMALIZER_STRIP_ACCENTS, normalizer_opts.strip_accents, false);
 
+        {
+            std::string scheme;
+            if (ml.get_key(LLM_KV_TOKENIZER_METASPACE_PREPEND_SCHEME, scheme, false)) {
+                if (scheme == "never") {
+                    metaspace_prepend_scheme = LLAMA_METASPACE_PREPEND_SCHEME_NEVER;
+                } else if (scheme == "first") {
+                    metaspace_prepend_scheme = LLAMA_METASPACE_PREPEND_SCHEME_FIRST;
+                } else if (scheme == "always") {
+                    metaspace_prepend_scheme = LLAMA_METASPACE_PREPEND_SCHEME_ALWAYS;
+                } else {
+                    throw std::runtime_error(format("unknown metaspace prepend_scheme: '%s'", scheme.c_str()));
+                }
+                if (type == LLAMA_VOCAB_TYPE_BPE && metaspace_prepend_scheme == LLAMA_METASPACE_PREPEND_SCHEME_ALWAYS) {
+                    throw std::runtime_error("metaspace prepend_scheme 'always' is not supported for BPE vocab");
+                }
+            }
+        }
+
         // suppress tokens
         {
             const int suppress_idx = gguf_find_key(ctx, kv(LLM_KV_TOKENIZER_SUPPRESS_TOKENS).c_str());
@@ -3743,6 +3768,7 @@ std::vector<llama_token> llama_vocab::impl::tokenize(
                 // tokenizer.encode('', add_special_tokens=True)  returns [1]
                 // tokenizer.encode('', add_special_tokens=False) returns []
 
+                // TODO: honor metaspace_prepend_scheme (add_space_prefix currently behaves like "always")
                 bool is_prev_special = true;  // prefix with space if first token
 
                 if (add_special && add_bos) {
@@ -3813,6 +3839,13 @@ std::vector<llama_token> llama_vocab::impl::tokenize(
                             llama_escape_whitespace(text);
                         }
 
+                        // Metaspace prepend_scheme "first": add U+2581 only at the start of the input
+                        static const std::string escaped_space = "\xE2\x96\x81";
+                        if (metaspace_prepend_scheme == LLAMA_METASPACE_PREPEND_SCHEME_FIRST &&
+                            &fragment == &fragment_buffer.front() && text.rfind(escaped_space, 0) != 0) {
+                            text.insert(0, escaped_space);
+                        }
+
 #ifdef PRETOKENIZERDEBUG
                         LLAMA_LOG_WARN("TT: (%ld %ld %ld) '%s'\n", text.length(), fragment.offset, fragment.length, text.c_str());
 #endif
@@ -3860,6 +3893,7 @@ std::vector<llama_token> llama_vocab::impl::tokenize(
                     GGML_ASSERT(special_bos_id != LLAMA_TOKEN_NULL);
                     output.push_back(special_bos_id);
                 }
+                // TODO: honor metaspace_prepend_scheme
                 llm_tokenizer_ugm_session session(vocab, *static_cast<const llm_tokenizer_ugm *>(tokenizer.get()));
 
                 for (const auto & fragment : fragment_buffer) {
@@ -4143,10 +4177,17 @@ int32_t llama_vocab::impl::detokenize(
         }
     }
 
+    // Metaspace prepend_scheme "first": remove the leading space of the first rendered piece, so a skipped BOS does not consume it
+    // TODO: honor metaspace_prepend_scheme for the other vocab types
+    bool remove_first_space = type == LLAMA_VOCAB_TYPE_BPE && metaspace_prepend_scheme == LLAMA_METASPACE_PREPEND_SCHEME_FIRST;
+
     for (int32_t i = 0; i < n_tokens; ++i) {
         GGML_ASSERT(avail >= 0);
-        int32_t n_chars = token_to_piece(tokens[i], text, avail, remove_space, unparse_special);
+        int32_t n_chars = token_to_piece(tokens[i], text, avail, remove_space || remove_first_space, unparse_special);
         remove_space = false;
+        if (unparse_special || !(token_get_attr(tokens[i]) & (LLAMA_TOKEN_ATTR_UNKNOWN | LLAMA_TOKEN_ATTR_CONTROL))) {
+            remove_first_space = false;
+        }
         if (n_chars < 0) {
             avail = 0;
             total -= n_chars;

src/llama-vocab.h

@@ -71,6 +71,14 @@ enum llama_vocab_pre_type {
     LLAMA_VOCAB_PRE_TYPE_MMBERT            = 60,
     LLAMA_VOCAB_PRE_TYPE_K2_HORIZON        = 61,
     LLAMA_VOCAB_PRE_TYPE_FLINT             = 62,
+    LLAMA_VOCAB_PRE_TYPE_DOMYN_SMALL       = 63,
+};
+
+// HF Metaspace pre-tokenizer prepend_scheme
+enum llama_metaspace_prepend_scheme {
+    LLAMA_METASPACE_PREPEND_SCHEME_NEVER  = 0,
+    LLAMA_METASPACE_PREPEND_SCHEME_FIRST  = 1,
+    LLAMA_METASPACE_PREPEND_SCHEME_ALWAYS = 2,
 };
 
 struct LLM_KV;

src/models/nemotron.cpp

@@ -25,8 +25,11 @@ void llama_model_nemotron::load_arch_tensors(llama_model_loader &) {
         layer.attn_norm   = create_tensor(tn(LLM_TENSOR_ATTN_NORM, "weight", i), {n_embd}, 0);
         layer.attn_norm_b = create_tensor(tn(LLM_TENSOR_ATTN_NORM, "bias", i), {n_embd}, 0);
 
-        create_tensor_qkv(layer, i, n_embd, n_embd, n_embd_gqa, n_embd_gqa, 0);
+        // n_embd_head_k * n_head equals n_embd for standard Nemotron (32 heads),
-        layer.wo = create_tensor(tn(LLM_TENSOR_ATTN_OUT, "weight", i), {n_embd, n_embd}, 0);
+        // but differs for models with non-standard GQA (e.g. 48 Q heads, head_dim=128).
+        const int64_t n_embd_q = n_embd_head_k * n_head;
+        create_tensor_qkv(layer, i, n_embd, n_embd_q, n_embd_gqa, n_embd_gqa, 0);
+        layer.wo = create_tensor(tn(LLM_TENSOR_ATTN_OUT, "weight", i), {n_embd_q, n_embd}, 0);
 
         // optional bias tensors
         layer.wo_b = create_tensor(tn(LLM_TENSOR_ATTN_OUT, "bias", i), {n_embd}, TENSOR_NOT_REQUIRED);