Chess Challenge submission by swdo

README.md

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+---
+library_name: transformers
+tags:
+- chess
+- llm-course
+- chess-challenge
+license: mit
+---
+
+# chess_swdo_subTok
+
+Chess model submitted to the LLM Course Chess Challenge.
+
+## Submission Info
+
+- **Submitted by**: [swdo](https://huggingface.co/swdo)
+- **Parameters**: 705,792
+- **Organization**: LLM-course
+
+## Model Details
+
+- **Architecture**: Chess Transformer (GPT-style)
+- **Vocab size**: 88
+- **Embedding dim**: 128
+- **Layers**: 4
+- **Heads**: 4

config.json

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+{
+  "architectures": [
+    "ChessForCausalLM"
+  ],
+  "bos_token_id": 1,
+  "dropout": 0.1,
+  "dtype": "float32",
+  "eos_token_id": 2,
+  "layer_norm_epsilon": 1e-05,
+  "model_type": "chess_transformer",
+  "n_ctx": 256,
+  "n_embd": 128,
+  "n_head": 4,
+  "n_inner": 384,
+  "n_layer": 4,
+  "pad_token_id": 0,
+  "tie_weights": true,
+  "transformers_version": "4.57.3",
+  "vocab_size": 88,
+  "auto_map": {
+    "AutoConfig": "model.ChessConfig",
+    "AutoModelForCausalLM": "model.ChessForCausalLM"
+  }
+}

model.py

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+"""
+Chess Transformer Model for the Chess Challenge.
+
+This module provides a simple GPT-style transformer architecture
+designed to fit within the 1M parameter constraint.
+
+Key components:
+- ChessConfig: Configuration class for model hyperparameters
+- ChessForCausalLM: The main model class for next-move prediction
+"""
+
+from __future__ import annotations
+
+import math
+from dataclasses import dataclass
+from typing import Optional, Tuple, Union
+
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+from transformers import PretrainedConfig, PreTrainedModel
+from transformers.modeling_outputs import CausalLMOutputWithPast
+
+
+class ChessConfig(PretrainedConfig):
+    """
+    Configuration class for the Chess Transformer model.
+    
+    This configuration is designed for a ~1M parameter model.
+    Students can adjust these values to explore different architectures.
+    
+    Parameter budget breakdown (with default values):
+    - Embeddings (vocab): 1200 x 128 = 153,600
+    - Position Embeddings: 256 x 128 = 32,768
+    - Transformer Layers: 6 x ~120,000 = ~720,000
+    - LM Head (with weight tying): 0 (shared with embeddings)
+    - Total: ~906,000 parameters
+    
+    Attributes:
+        vocab_size: Size of the vocabulary (number of unique moves).
+        n_embd: Embedding dimension (d_model).
+        n_layer: Number of transformer layers.
+        n_head: Number of attention heads.
+        n_ctx: Maximum sequence length (context window).
+        n_inner: Feed-forward inner dimension (default: 3 * n_embd).
+        dropout: Dropout probability.
+        layer_norm_epsilon: Epsilon for layer normalization.
+        tie_weights: Whether to tie embedding and output weights.
+    """
+    
+    model_type = "chess_transformer"
+    
+    def __init__(
+        self,
+        vocab_size: int = 1200,
+        n_embd: int = 128,
+        n_layer: int = 6,
+        n_head: int = 4,
+        n_ctx: int = 256,
+        n_inner: Optional[int] = None,
+        dropout: float = 0.1,
+        layer_norm_epsilon: float = 1e-5,
+        tie_weights: bool = True,
+        pad_token_id: int = 0,
+        bos_token_id: int = 1,
+        eos_token_id: int = 2,
+        **kwargs,
+    ):
+        super().__init__(
+            pad_token_id=pad_token_id,
+            bos_token_id=bos_token_id,
+            eos_token_id=eos_token_id,
+            **kwargs,
+        )
+        
+        self.vocab_size = vocab_size
+        self.n_embd = n_embd
+        self.n_layer = n_layer
+        self.n_head = n_head
+        self.n_ctx = n_ctx
+        self.n_inner = n_inner if n_inner is not None else 3 * n_embd  # Reduced from 4x to 3x
+        self.dropout = dropout
+        self.layer_norm_epsilon = layer_norm_epsilon
+        self.tie_weights = tie_weights
+        # Inform HF base class about tying behavior
+        self.tie_word_embeddings = bool(tie_weights)
+
+
+class MultiHeadAttention(nn.Module):
+    """
+    Multi-head self-attention module.
+    
+    This is a standard scaled dot-product attention implementation
+    with causal masking for autoregressive generation.
+    """
+    
+    def __init__(self, config: ChessConfig):
+        super().__init__()
+        
+        assert config.n_embd % config.n_head == 0, \
+            f"n_embd ({config.n_embd}) must be divisible by n_head ({config.n_head})"
+        
+        self.n_head = config.n_head
+        self.n_embd = config.n_embd
+        self.head_dim = config.n_embd // config.n_head
+        
+        # Combined QKV projection for efficiency
+        self.c_attn = nn.Linear(config.n_embd, 3 * config.n_embd)
+        self.c_proj = nn.Linear(config.n_embd, config.n_embd)
+        
+        self.dropout = nn.Dropout(config.dropout)
+        
+        # Causal mask (will be created on first forward pass)
+        self.register_buffer(
+            "bias",
+            torch.tril(torch.ones(config.n_ctx, config.n_ctx)).view(
+                1, 1, config.n_ctx, config.n_ctx
+            ),
+            persistent=False,
+        )
+    
+    def forward(
+        self,
+        x: torch.Tensor,
+        attention_mask: Optional[torch.Tensor] = None,
+    ) -> torch.Tensor:
+        batch_size, seq_len, _ = x.size()
+        
+        # Compute Q, K, V
+        qkv = self.c_attn(x)
+        q, k, v = qkv.split(self.n_embd, dim=2)
+        
+        # Reshape for multi-head attention
+        q = q.view(batch_size, seq_len, self.n_head, self.head_dim).transpose(1, 2)
+        k = k.view(batch_size, seq_len, self.n_head, self.head_dim).transpose(1, 2)
+        v = v.view(batch_size, seq_len, self.n_head, self.head_dim).transpose(1, 2)
+        
+        # Scaled dot-product attention
+        attn_weights = torch.matmul(q, k.transpose(-2, -1)) / math.sqrt(self.head_dim)
+        
+        # Apply causal mask
+        causal_mask = self.bias[:, :, :seq_len, :seq_len]
+        attn_weights = attn_weights.masked_fill(causal_mask == 0, float("-inf"))
+        
+        # Apply attention mask (for padding)
+        if attention_mask is not None:
+            # attention_mask shape: (batch_size, seq_len) -> (batch_size, 1, 1, seq_len)
+            attention_mask = attention_mask.unsqueeze(1).unsqueeze(2)
+            attn_weights = attn_weights.masked_fill(attention_mask == 0, float("-inf"))
+        
+        attn_weights = F.softmax(attn_weights, dim=-1)
+        attn_weights = self.dropout(attn_weights)
+        
+        # Apply attention to values
+        attn_output = torch.matmul(attn_weights, v)
+        
+        # Reshape back
+        attn_output = attn_output.transpose(1, 2).contiguous().view(
+            batch_size, seq_len, self.n_embd
+        )
+        
+        # Output projection
+        attn_output = self.c_proj(attn_output)
+        
+        return attn_output
+
+
+class FeedForward(nn.Module):
+    """
+    Feed-forward network (MLP) module.
+    
+    Standard two-layer MLP with GELU activation.
+    """
+    
+    def __init__(self, config: ChessConfig):
+        super().__init__()
+        
+        self.c_fc = nn.Linear(config.n_embd, config.n_inner)
+        self.c_proj = nn.Linear(config.n_inner, config.n_embd)
+        self.dropout = nn.Dropout(config.dropout)
+    
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        x = self.c_fc(x)
+        x = F.gelu(x)
+        x = self.c_proj(x)
+        x = self.dropout(x)
+        return x
+
+
+class TransformerBlock(nn.Module):
+    """
+    A single transformer block with attention and feed-forward layers.
+    
+    Uses pre-normalization (LayerNorm before attention/FFN) for better
+    training stability.
+    """
+    
+    def __init__(self, config: ChessConfig):
+        super().__init__()
+        
+        self.ln_1 = nn.LayerNorm(config.n_embd, eps=config.layer_norm_epsilon)
+        self.attn = MultiHeadAttention(config)
+        self.ln_2 = nn.LayerNorm(config.n_embd, eps=config.layer_norm_epsilon)
+        self.mlp = FeedForward(config)
+    
+    def forward(
+        self,
+        x: torch.Tensor,
+        attention_mask: Optional[torch.Tensor] = None,
+    ) -> torch.Tensor:
+        # Pre-norm attention
+        x = x + self.attn(self.ln_1(x), attention_mask=attention_mask)
+        # Pre-norm FFN
+        x = x + self.mlp(self.ln_2(x))
+        return x
+
+
+class ChessForCausalLM(PreTrainedModel):
+    """
+    Chess Transformer for Causal Language Modeling (next-move prediction).
+    
+    This model is designed to predict the next chess move given a sequence
+    of previous moves. It uses a GPT-style architecture with:
+    - Token embeddings for chess moves
+    - Learned positional embeddings
+    - Stacked transformer blocks
+    - Linear head for next-token prediction
+    
+    The model supports weight tying between the embedding layer and the
+    output projection to save parameters.
+    
+    Example:
+        >>> config = ChessConfig(vocab_size=1200, n_embd=128, n_layer=6)
+        >>> model = ChessForCausalLM(config)
+        >>> inputs = {"input_ids": torch.tensor([[1, 42, 87]])}
+        >>> outputs = model(**inputs)
+        >>> next_move_logits = outputs.logits[:, -1, :]
+    """
+    
+    config_class = ChessConfig
+    base_model_prefix = "transformer"
+    supports_gradient_checkpointing = True
+    # Suppress missing-key warning for tied lm_head when loading
+    keys_to_ignore_on_load_missing = ["lm_head.weight"]
+    
+    def __init__(self, config: ChessConfig):
+        super().__init__(config)
+        
+        # Token and position embeddings
+        self.wte = nn.Embedding(config.vocab_size, config.n_embd)
+        self.wpe = nn.Embedding(config.n_ctx, config.n_embd)
+        
+        self.drop = nn.Dropout(config.dropout)
+        
+        # Transformer blocks
+        self.h = nn.ModuleList([
+            TransformerBlock(config) for _ in range(config.n_layer)
+        ])
+        
+        # Final layer norm
+        self.ln_f = nn.LayerNorm(config.n_embd, eps=config.layer_norm_epsilon)
+        
+        # Output head
+        self.lm_head = nn.Linear(config.n_embd, config.vocab_size, bias=False)
+        
+        # Declare tied weights for proper serialization
+        if config.tie_weights:
+            self._tied_weights_keys = ["lm_head.weight"]
+        
+        # Initialize weights
+        self.post_init()
+        
+        # Tie weights if configured
+        if config.tie_weights:
+            self.tie_weights()
+
+    def get_input_embeddings(self) -> nn.Module:
+        return self.wte
+
+    def set_input_embeddings(self, new_embeddings: nn.Module):
+        self.wte = new_embeddings
+        if getattr(self.config, "tie_weights", False):
+            self.tie_weights()
+
+    def get_output_embeddings(self) -> nn.Module:
+        return self.lm_head
+
+    def set_output_embeddings(self, new_embeddings: nn.Module):
+        self.lm_head = new_embeddings
+
+    def tie_weights(self):
+        # Use HF helper to tie or clone depending on config
+        if getattr(self.config, "tie_weights", False) or getattr(self.config, "tie_word_embeddings", False):
+            self._tie_or_clone_weights(self.lm_head, self.wte)
+    
+    def _init_weights(self, module: nn.Module):
+        """Initialize weights following GPT-2 style."""
+        if isinstance(module, nn.Linear):
+            torch.nn.init.normal_(module.weight, mean=0.0, std=0.02)
+            if module.bias is not None:
+                torch.nn.init.zeros_(module.bias)
+        elif isinstance(module, nn.Embedding):
+            torch.nn.init.normal_(module.weight, mean=0.0, std=0.02)
+        elif isinstance(module, nn.LayerNorm):
+            torch.nn.init.ones_(module.weight)
+            torch.nn.init.zeros_(module.bias)
+    
+    def forward(
+        self,
+        input_ids: torch.LongTensor,
+        attention_mask: Optional[torch.Tensor] = None,
+        position_ids: Optional[torch.LongTensor] = None,
+        labels: Optional[torch.LongTensor] = None,
+        return_dict: Optional[bool] = None,
+        **kwargs,
+    ) -> Union[Tuple, CausalLMOutputWithPast]:
+        """
+        Forward pass of the model.
+        
+        Args:
+            input_ids: Token IDs of shape (batch_size, seq_len).
+            attention_mask: Attention mask of shape (batch_size, seq_len).
+            position_ids: Position IDs of shape (batch_size, seq_len).
+            labels: Labels for language modeling loss.
+            return_dict: Whether to return a ModelOutput object.
+        
+        Returns:
+            CausalLMOutputWithPast containing loss (if labels provided) and logits.
+        """
+        return_dict = return_dict if return_dict is not None else self.config.use_return_dict
+        
+        batch_size, seq_len = input_ids.size()
+        device = input_ids.device
+        
+        # Create position IDs if not provided
+        if position_ids is None:
+            position_ids = torch.arange(seq_len, device=device).unsqueeze(0).expand(batch_size, -1)
+        
+        # Get embeddings
+        token_embeds = self.wte(input_ids)
+        position_embeds = self.wpe(position_ids)
+        hidden_states = self.drop(token_embeds + position_embeds)
+        
+        # Pass through transformer blocks
+        for block in self.h:
+            hidden_states = block(hidden_states, attention_mask=attention_mask)
+        
+        # Final layer norm
+        hidden_states = self.ln_f(hidden_states)
+        
+        # Get logits
+        logits = self.lm_head(hidden_states)
+        
+        # Compute loss if labels are provided
+        loss = None
+        if labels is not None:
+            # Shift logits and labels for next-token prediction
+            shift_logits = logits[..., :-1, :].contiguous()
+            shift_labels = labels[..., 1:].contiguous()
+            
+            # Flatten for cross-entropy
+            loss_fct = nn.CrossEntropyLoss(ignore_index=-100) #self.config.pad_token_id)
+            loss = loss_fct(
+                shift_logits.view(-1, shift_logits.size(-1)),
+                shift_labels.view(-1),
+            )
+        
+        if not return_dict:
+            output = (logits,)
+            return ((loss,) + output) if loss is not None else output
+        
+        return CausalLMOutputWithPast(
+            loss=loss,
+            logits=logits,
+            past_key_values=None,
+            hidden_states=None,
+            attentions=None,
+        )
+    
+    @torch.no_grad()
+    def generate_move(
+        self,
+        input_ids: torch.LongTensor,
+        temperature: float = 1.0,
+        top_k: Optional[int] = None,
+        top_p: Optional[float] = None,
+    ) -> int:
+        """
+        Generate the next move given a sequence of moves.
+        
+        Args:
+            input_ids: Token IDs of shape (1, seq_len).
+            temperature: Sampling temperature (1.0 = no change).
+            top_k: If set, only sample from top k tokens.
+            top_p: If set, use nucleus sampling with this threshold.
+        
+        Returns:
+            The token ID of the predicted next move.
+        """
+        self.eval()
+        
+        # Get logits for the last position
+        outputs = self(input_ids)
+        logits = outputs.logits[:, -1, :] / temperature
+        
+        # Apply top-k filtering
+        if top_k is not None:
+            indices_to_remove = logits < torch.topk(logits, top_k)[0][..., -1, None]
+            logits[indices_to_remove] = float("-inf")
+        
+        # Apply top-p (nucleus) filtering
+        if top_p is not None:
+            sorted_logits, sorted_indices = torch.sort(logits, descending=True)
+            cumulative_probs = torch.cumsum(F.softmax(sorted_logits, dim=-1), dim=-1)
+            
+            # Remove tokens with cumulative probability above the threshold
+            sorted_indices_to_remove = cumulative_probs > top_p
+            sorted_indices_to_remove[..., 1:] = sorted_indices_to_remove[..., :-1].clone()
+            sorted_indices_to_remove[..., 0] = 0
+            
+            indices_to_remove = sorted_indices_to_remove.scatter(
+                dim=-1, index=sorted_indices, src=sorted_indices_to_remove
+            )
+            logits[indices_to_remove] = float("-inf")
+        
+        # Sample from the distribution
+        probs = F.softmax(logits, dim=-1)
+        next_token = torch.multinomial(probs, num_samples=1)
+        
+        return next_token.item()
+
+
+# Register the model with Auto classes for easy loading
+from transformers import AutoConfig, AutoModelForCausalLM
+
+AutoConfig.register("chess_transformer", ChessConfig)
+AutoModelForCausalLM.register(ChessConfig, ChessForCausalLM)

model.safetensors

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+version https://git-lfs.github.com/spec/v1
+oid sha256:8d969df211c037f308c4b375eace7f2db2fb75587f112966b2bac08b0574c87d
+size 2827568

special_tokens_map.json

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+{
+  "bos_token": "[BOS]",
+  "eos_token": "[EOS]",
+  "pad_token": "[PAD]",
+  "unk_token": "[UNK]"
+}

tokenizer.py

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+"""
+Decomposed Chess Tokenizer v2 for the Chess Challenge.
+
+This tokenizer decomposes moves into structural components:
+- Color (W/B)
+- Piece (P/N/B/R/Q/K)
+- From square (a1-h8)
+- To square (a1-h8)
+- Modifiers (capture, check, checkmate, promotion, castling)
+
+This allows the model to learn chess structure and generalize better
+while using a much smaller vocabulary (~90 tokens vs ~1200+).
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import re
+from pathlib import Path
+from typing import Dict, List, Optional, Tuple
+
+from transformers import PreTrainedTokenizer
+
+
+class ChessTokenizer(PreTrainedTokenizer):
+    """
+    Decomposed chess move tokenizer.
+    
+    Breaks moves into structural components for better learning.
+    
+    Example:
+        >>> tokenizer = ChessTokenizer()
+        >>> tokens = tokenizer.tokenize("WPe2e4 BPe7e5")
+        >>> print(tokens)
+        ['W', 'P', 'e2', 'e4', 'B', 'P', 'e7', 'e5']
+        
+        >>> tokenizer.encode("WNg1f3(+)")
+        [1, 5, 8, 39, 29, 12, 2]  # [BOS, W, N, g1, f3, +, EOS]
+    """
+    
+    model_input_names = ["input_ids", "attention_mask"]
+    vocab_files_names = {"vocab_file": "vocab.json"}
+    
+    # Special tokens
+    PAD_TOKEN = "[PAD]"
+    BOS_TOKEN = "[BOS]"
+    EOS_TOKEN = "[EOS]"
+    UNK_TOKEN = "[UNK]"
+    SEP_TOKEN = "[SEP]"  # Optional: separate moves
+    
+    # Chess components
+    # Use [W] and [B] for colors to avoid collision with piece 'B' (Bishop)
+    COLORS = ["[W]", "[B]"]
+    PIECES = ["P", "N", "B", "R", "Q", "K"]
+    FILES = ["a", "b", "c", "d", "e", "f", "g", "h"]
+    RANKS = ["1", "2", "3", "4", "5", "6", "7", "8"]
+    # Generate all 64 squares
+    SQUARES = [f + r for f in FILES for r in ["1", "2", "3", "4", "5", "6", "7", "8"]]
+    
+    # Modifiers
+    MODIFIERS = [
+        "x",      # Capture
+        "+",      # Check
+        "#",      # Checkmate (alternative to +*)
+        "+*",     # Checkmate (dataset format)
+        "=Q",     # Promotion to Queen
+        "=R",     # Promotion to Rook
+        "=B",     # Promotion to Bishop
+        "=N",     # Promotion to Knight
+        "O-O",    # Kingside castling (alternative)
+        "O-O-O",  # Queenside castling (alternative)
+        "o",      # Kingside castling (dataset format)
+        "O",      # Queenside castling (dataset format)
+    ]
+    
+    # Regex pattern to parse extended UCI moves
+    # Format: [W|B][Piece][from_sq][to_sq][promotion]?[suffixes]?
+    MOVE_PATTERN = re.compile(
+        r'^([WB])'                    # Color
+        r'([PNBRQK])'                 # Piece
+        r'([a-h][1-8])'               # From square
+        r'([a-h][1-8])'               # To square
+        r'(=[QRBN])?'                 # Promotion (optional)
+        r'(\([xoO+*]+\))?$'           # Suffixes in parentheses (optional)
+    )
+    
+    def __init__(
+        self,
+        vocab_file: Optional[str] = None,
+        vocab: Optional[Dict[str, int]] = None,
+        add_move_separator: bool = False,
+        **kwargs,
+    ):
+        """
+        Initialize the decomposed chess tokenizer.
+        
+        Args:
+            vocab_file: Path to vocabulary JSON file.
+            vocab: Pre-built vocabulary dictionary.
+            add_move_separator: Whether to add [SEP] between moves.
+        """
+        self._pad_token = self.PAD_TOKEN
+        self._bos_token = self.BOS_TOKEN
+        self._eos_token = self.EOS_TOKEN
+        self._unk_token = self.UNK_TOKEN
+        self.add_move_separator = add_move_separator
+        
+        # Remove duplicates from kwargs
+        kwargs.pop("pad_token", None)
+        kwargs.pop("bos_token", None)
+        kwargs.pop("eos_token", None)
+        kwargs.pop("unk_token", None)
+        
+        # Load or create vocabulary
+        if vocab is not None:
+            self._vocab = vocab
+        elif vocab_file is not None and os.path.exists(vocab_file):
+            with open(vocab_file, "r", encoding="utf-8") as f:
+                self._vocab = json.load(f)
+        else:
+            self._vocab = self._create_vocab()
+        
+        # Reverse mapping
+        self._ids_to_tokens = {v: k for k, v in self._vocab.items()}
+        
+        super().__init__(
+            pad_token=self._pad_token,
+            bos_token=self._bos_token,
+            eos_token=self._eos_token,
+            unk_token=self._unk_token,
+            **kwargs,
+        )
+    
+    def _create_vocab(self) -> Dict[str, int]:
+        """Create the fixed vocabulary from chess components."""
+        tokens = []
+        
+        # Special tokens first
+        tokens.extend([self.PAD_TOKEN, self.BOS_TOKEN, self.EOS_TOKEN, self.UNK_TOKEN])
+        if self.add_move_separator:
+            tokens.append(self.SEP_TOKEN)
+        
+        # Colors
+        tokens.extend(self.COLORS)
+        
+        # Pieces
+        tokens.extend(self.PIECES)
+        
+        # Squares (64)
+        tokens.extend(self.SQUARES)
+        
+        # Modifiers
+        tokens.extend(self.MODIFIERS)
+        
+        return {token: idx for idx, token in enumerate(tokens)}
+    
+    @property
+    def vocab_size(self) -> int:
+        return len(self._vocab)
+    
+    def get_vocab(self) -> Dict[str, int]:
+        return dict(self._vocab)
+    
+    def _parse_move(self, move: str) -> List[str]:
+        """
+        Parse a single move into component tokens.
+        
+        Args:
+            move: Move in extended UCI format (e.g., "WPe2e4", "BNg8f6(x+)")
+        
+        Returns:
+            List of component tokens.
+        """
+        match = self.MOVE_PATTERN.match(move)
+        
+        if not match:
+            # Fallback: return as unknown
+            return [self.UNK_TOKEN]
+        
+        tokens = []
+        
+        # Color - map 'W' -> '[W]' and 'B' -> '[B]' to avoid collision with piece Bishop
+        color = match.group(1)
+        tokens.append(f"[{color}]")
+        
+        # Piece
+        tokens.append(match.group(2))
+        
+        # From square
+        tokens.append(match.group(3))
+        
+        # To square
+        tokens.append(match.group(4))
+        
+        # Promotion (optional)
+        if match.group(5):
+            tokens.append(match.group(5))  # e.g., "=Q"
+        
+        # Parse suffixes (optional)
+        if match.group(6):
+            suffix = match.group(6)  # e.g., "(x+)"
+            # Remove parentheses
+            suffix_content = suffix[1:-1]
+            
+            # Parse individual modifiers
+            if "x" in suffix_content:
+                tokens.append("x")
+            if "+*" in suffix_content:
+                tokens.append("+*")
+            elif "+" in suffix_content:
+                tokens.append("+")
+            if suffix_content == "o":
+                tokens.append("o")
+            elif suffix_content == "O":
+                tokens.append("O")
+        
+        return tokens
+    
+    def _tokenize(self, text: str) -> List[str]:
+        """
+        Tokenize a string of moves.
+        
+        Args:
+            text: Space-separated moves in extended UCI format.
+        
+        Returns:
+            List of component tokens.
+        """
+        tokens = []
+        moves = text.strip().split()
+        
+        for i, move in enumerate(moves):
+            move_tokens = self._parse_move(move)
+            tokens.extend(move_tokens)
+            
+            # Add separator between moves (optional)
+            if self.add_move_separator and i < len(moves) - 1:
+                tokens.append(self.SEP_TOKEN)
+        
+        return tokens
+    
+    def _convert_token_to_id(self, token: str) -> int:
+        return self._vocab.get(token, self._vocab.get(self.UNK_TOKEN, 0))
+    
+    def _convert_id_to_token(self, index: int) -> str:
+        return self._ids_to_tokens.get(index, self.UNK_TOKEN)
+    
+    def convert_tokens_to_string(self, tokens: List[str]) -> str:
+        """
+        Convert tokens back to move string.
+        
+        Reconstructs moves from component tokens.
+        """
+        special = {self.PAD_TOKEN, self.BOS_TOKEN, self.EOS_TOKEN, self.UNK_TOKEN, self.SEP_TOKEN}
+        
+        result = []
+        current_move = []
+        
+        for token in tokens:
+            if token in special:
+                if current_move:
+                    result.append(self._reconstruct_move(current_move))
+                    current_move = []
+                continue
+            
+            current_move.append(token)
+            
+            # Check if we have a complete move
+            if self._is_complete_move(current_move):
+                result.append(self._reconstruct_move(current_move))
+                current_move = []
+        
+        # Handle remaining tokens
+        if current_move:
+            result.append(self._reconstruct_move(current_move))
+        
+        return " ".join(result)
+    
+    def _is_complete_move(self, tokens: List[str]) -> bool:
+        """Check if tokens form a complete move."""
+        if len(tokens) < 4:
+            return False
+        
+        # Basic move: Color + Piece + From + To
+        if (tokens[0] in self.COLORS and 
+            tokens[1] in self.PIECES and
+            tokens[2] in self.SQUARES and
+            tokens[3] in self.SQUARES):
+            
+            # Check if next token would start a new move
+            if len(tokens) == 4:
+                return True
+            
+            # Check for modifiers
+            remaining = tokens[4:]
+            for t in remaining:
+                if t in self.COLORS:
+                    return True  # Next move starting
+                if t not in self.MODIFIERS and not t.startswith("="):
+                    return True
+            
+            return True
+        
+        return False
+    
+    def _reconstruct_move(self, tokens: List[str]) -> str:
+        """Reconstruct a move string from component tokens."""
+        if not tokens:
+            return ""
+        
+        # Basic structure: Color + Piece + From + To
+        if len(tokens) >= 4:
+            # Convert [W] -> W and [B] -> B for colors
+            color = tokens[0]
+            if color in self.COLORS:
+                color = color[1]  # Extract 'W' from '[W]' or 'B' from '[B]'
+            
+            move = color + "".join(tokens[1:4])
+            
+            # Add modifiers
+            suffixes = []
+            for t in tokens[4:]:
+                if t.startswith("="):
+                    move += t
+                elif t in ["x", "+", "+*", "o", "O"]:
+                    suffixes.append(t)
+            
+            if suffixes:
+                move += "(" + "".join(suffixes) + ")"
+            
+            return move
+        
+        return "".join(tokens)
+    
+    def save_vocabulary(
+        self,
+        save_directory: str,
+        filename_prefix: Optional[str] = None,
+    ) -> Tuple[str]:
+        if not os.path.isdir(save_directory):
+            os.makedirs(save_directory, exist_ok=True)
+        
+        vocab_file = os.path.join(
+            save_directory,
+            (filename_prefix + "-" if filename_prefix else "") + "vocab.json",
+        )
+        
+        with open(vocab_file, "w", encoding="utf-8") as f:
+            json.dump(self._vocab, f, ensure_ascii=False, indent=2)
+        
+        # Also save config with auto_map for HuggingFace to find our custom tokenizer
+        # Format: (slow_tokenizer_class, fast_tokenizer_class) - we don't have a fast version
+        config = {
+            "tokenizer_class": "ChessTokenizer",
+            "auto_map": {
+                "AutoTokenizer": ["tokenizer.ChessTokenizer", None]
+            },
+            "add_move_separator": self.add_move_separator,
+            "vocab_size": self.vocab_size,
+        }
+        config_file = os.path.join(save_directory, "tokenizer_config.json")
+        with open(config_file, "w", encoding="utf-8") as f:
+            json.dump(config, f, indent=2)
+        
+        return (vocab_file,)
+    
+    @classmethod
+    def from_pretrained(cls, pretrained_model_name_or_path, **kwargs):
+        """Load tokenizer from directory or hub."""
+        path = Path(pretrained_model_name_or_path)
+        
+        if path.is_dir():
+            vocab_file = path / "vocab.json"
+            config_file = path / "tokenizer_config.json"
+            
+            add_move_separator = False
+            if config_file.exists():
+                with open(config_file, "r") as f:
+                    config = json.load(f)
+                    add_move_separator = config.get("add_move_separator", False)
+            
+            return cls(
+                vocab_file=str(vocab_file) if vocab_file.exists() else None,
+                add_move_separator=add_move_separator,
+                **kwargs,
+            )
+        
+        # Fallback to HuggingFace hub
+        from huggingface_hub import hf_hub_download
+        
+        vocab_file = hf_hub_download(
+            repo_id=pretrained_model_name_or_path,
+            filename="vocab.json",
+        )
+        
+        return cls(vocab_file=vocab_file, **kwargs)
+

tokenizer_config.json

@@ -0,0 +1,11 @@
+{
+  "tokenizer_class": "ChessTokenizer",
+  "auto_map": {
+    "AutoTokenizer": [
+      "tokenizer.ChessTokenizer",
+      null
+    ]
+  },
+  "add_move_separator": false,
+  "vocab_size": 88
+}

vocab.json

@@ -0,0 +1,90 @@
+{
+  "[PAD]": 0,
+  "[BOS]": 1,
+  "[EOS]": 2,
+  "[UNK]": 3,
+  "[W]": 4,
+  "[B]": 5,
+  "P": 6,
+  "N": 7,
+  "B": 8,
+  "R": 9,
+  "Q": 10,
+  "K": 11,
+  "a1": 12,
+  "a2": 13,
+  "a3": 14,
+  "a4": 15,
+  "a5": 16,
+  "a6": 17,
+  "a7": 18,
+  "a8": 19,
+  "b1": 20,
+  "b2": 21,
+  "b3": 22,
+  "b4": 23,
+  "b5": 24,
+  "b6": 25,
+  "b7": 26,
+  "b8": 27,
+  "c1": 28,
+  "c2": 29,
+  "c3": 30,
+  "c4": 31,
+  "c5": 32,
+  "c6": 33,
+  "c7": 34,
+  "c8": 35,
+  "d1": 36,
+  "d2": 37,
+  "d3": 38,
+  "d4": 39,
+  "d5": 40,
+  "d6": 41,
+  "d7": 42,
+  "d8": 43,
+  "e1": 44,
+  "e2": 45,
+  "e3": 46,
+  "e4": 47,
+  "e5": 48,
+  "e6": 49,
+  "e7": 50,
+  "e8": 51,
+  "f1": 52,
+  "f2": 53,
+  "f3": 54,
+  "f4": 55,
+  "f5": 56,
+  "f6": 57,
+  "f7": 58,
+  "f8": 59,
+  "g1": 60,
+  "g2": 61,
+  "g3": 62,
+  "g4": 63,
+  "g5": 64,
+  "g6": 65,
+  "g7": 66,
+  "g8": 67,
+  "h1": 68,
+  "h2": 69,
+  "h3": 70,
+  "h4": 71,
+  "h5": 72,
+  "h6": 73,
+  "h7": 74,
+  "h8": 75,
+  "x": 76,
+  "+": 77,
+  "#": 78,
+  "+*": 79,
+  "=Q": 80,
+  "=R": 81,
+  "=B": 82,
+  "=N": 83,
+  "O-O": 84,
+  "O-O-O": 85,
+  "o": 86,
+  "O": 87
+}