Reference implementation and checkpoint configuration deepseek-ai/DeepSeek-V4.1-Flash @ 2cba9e4 · parameter count checked against the checkpoint’s tensor headers · text model only · How to read

N-gram hashes

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no parametersself.engram_hash(input_ids, start_pos, engram_mask) · 1252

For each position, hash the 2-, 3- and 4-gram of normalized tokens ending there into 8 row indices each, for each Engram table.

Nt,ℓ,(g,h)=(⨁i=0g−1μℓ,i ct−i) mod Pℓ,g,h+oℓ,g,hN_{t,\ell,(g,h)}=\Big(\bigoplus_{i=0}^{g-1}\mu_{\ell,i}\,c_{t-i}\Big)\bmod P_{\ell,g,h}+o_{\ell,g,h}
g=2..4,  h=1..8g=2..4,\;h=1..8
in
II [B batch, T positions]cc [B batch, T positions]
out
NN [B batch, T positions, 2 Engram layers, 24 n-grams × heads]

Token IDs are first mapped to 99,092 normalized IDs, so that tokens whose text differs only in case, accents or spacing share one (engram.py 17–61); the vocabulary file needed to rebuild that map is not pinned. An n-gram does not reach across the start of the sequence or an image position. The normalized IDs are written to a buffer kept between calls and read back from it, so that a later call can reach this call’s tokens (engram.py 167, 172).

Codeengram.py 159–184 · 2 more files
engram.py 159–184
    @torch.inference_mode()
    def forward(self, input_ids: torch.Tensor, start_pos: int, token_mask: torch.Tensor | None = None) -> torch.Tensor:
        """token_mask: [B, L], False for tokens that take no part in an n-gram (image spans).
        Returns the hash ids, shaped [B, L, n_engram_layers, n_hash_cols]."""
        batch, seqlen = input_ids.shape
        compressed = self.token_map[input_ids]
        if token_mask is not None:
            compressed = torch.where(token_mask, compressed, self.DEAD)
        self.cache[:batch, start_pos : start_pos + seqlen] = compressed

        positions = torch.arange(start_pos, start_pos + seqlen, device=input_ids.device).expand(batch, seqlen)
        tokens, blocked = [], torch.zeros_like(positions, dtype=torch.bool)
        for shift in range(self.layout.max_ngram_size):
            source = self.cache[:batch].gather(1, (positions - shift).clamp_min(0))
            blocked = blocked | (positions < shift) | (source == self.DEAD)
            tokens.append(torch.where(blocked, self.pad_id, source))
        tokens = torch.stack(tokens, dim=-1)  # [B, L, max_ngram_size]

        # XOR the multiplied ids together one lookback at a time, so the running value after step i
        # is the hash of the (i+1)-gram; each lands in its own prime-sized bucket range
        products = tokens.unsqueeze(2) * self.multipliers  # [B, L, n_engram_layers, max_ngram_size]
        rolling, hashes = products[..., 0], []
        for i in range(1, self.layout.max_ngram_size):
            rolling = torch.bitwise_xor(rolling, products[..., i])
            hashes.append(rolling.unsqueeze(-1) % self.primes[:, i - 1])
        return torch.cat(hashes, dim=-1) + self.offsets
model.py 1241–1272
    @torch.inference_mode()
    def forward(
        self, input_ids: torch.Tensor, start_pos: int = 0, images=None, token_types: torch.Tensor | None = None
    ):
        """input_ids: [b, s], every entry a real token id -- generate.py only ever passes positions it
        has already filled, so the padding it uses internally never reaches here. token_types /
        images carry the VL inputs built by image_processor.prepare_vl_inputs; image spans must lie
        inside the first (start_pos 0) chunk."""
        image_mask = None if token_types is None else token_types >= 0  # TEXT is -1
        # image tokens take no part in an n-gram and get no engram contribution; text-only needs no mask
        engram_mask = None if image_mask is None else ~image_mask
        engram_hashes = self.engram_hash(input_ids, start_pos, engram_mask) if self.engram_hash is not None else None
        h = self.embed(input_ids)
        if images is not None:
            assert start_pos == 0, "image spans must be prefilled in a single chunk"
            self.merge_image_embeddings(images, h)
        # Expand to hc_mult copies for Hyper-Connections
        h = h.unsqueeze(2).repeat(1, 1, self.hc_mult, 1)
        main_hiddens = []
        pre_mix = make_identity_pre_mix(h, self.hc_mult)
        for i, layer in enumerate(self.layers):
            if layer.engram is not None:
                h = layer.engram(h, engram_hashes[:, :, layer.engram.layer_hash_index, :], engram_mask)
            # the MTP head reads the attention input of its target layers, not their output
            if i in self.target_layer_ids:
                main_hiddens.append(h.mean(dim=2))
            h, pre_mix = layer(h, start_pos, pre_mix, image_mask)
        h = layer.hc_pre(h, pre_mix)
        logits = self.head(self.norm(h))
        output_ids = sample(logits, self.temperature)
        main_hidden = torch.cat(main_hiddens, dim=-1) if main_hiddens else None
        return output_ids, logits, main_hidden
config.json 1–66
{
    "vocab_size": 129280,
    "dim": 5120,
    "moe_inter_dim": 2304,
    "n_layers": 40,
    "n_mtp_layers": 3,
    "dspark_block_size": 5,
    "dspark_noise_token_id": 128799,
    "dspark_target_layer_ids": [37, 38, 39],
    "dspark_markov_rank": 256,
    "dspark_n_routed_experts": 128,
    "dspark_n_activated_experts": 3,
    "n_heads": 64,
    "n_routed_experts": 384,
    "n_shared_experts": 1,
    "n_activated_experts": 6,
    "score_func": "sqrtsoftplus",
    "route_scale": 1.5,
    "swiglu_limit": 10.0,
    "q_lora_rank": 1280,
    "head_dim": 512,
    "rope_head_dim": 64,
    "norm_eps": 1e-20,
    "o_groups": 8,
    "o_lora_rank": 1024,
    "window_size": 128,
    "kv_source_layers": [2, 8, 14, 20],
    "index_source_layers": [2, 8, 14, 20, 24, 28, 32, 36],
    "original_seq_len": 65536,
    "rope_theta": 10000,
    "rope_factor": 16,
    "beta_fast": 32,
    "beta_slow": 1,
    "index_n_heads": 32,
    "index_head_dim": 128,
    "index_topk": 512,
    "candidate_source_layer": 20,
    "candidate_topk_blocks": 2048,
    "candidate_block_size": 8,
    "hc_mult": 4,
    "hc_sinkhorn_iters": 20,
    "hc_eps": 1e-06,
    "engram_layer_ids": [1, 14],
    "engram_vocab_size": 16000000,
    "engram_num_embeddings": [384006168, 384016682],
    "engram_max_ngram_size": 4,
    "engram_pad_id": 2,
    "engram_compressed_vocab_size": 99092,
    "dtype": "fp8",
    "expert_dtype": "fp4",
    "compress_rope_theta": 160000,
    "compress_ratios": [0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0],
    "vision_n_layers": 32,
    "vision_dim": 1024,
    "vision_n_heads": 16,
    "vision_inter_dim": 2816,
    "vision_patch_size": 14,
    "vision_downsample_ratio": 3,
    "vision_max_n_token": 1024,
    "vision_min_pixels": 295936,
    "vision_max_wh_ratio": null,
    "image_token_id": 129264,
    "engram_n_heads": 8,
    "engram_head_dim": 256,
    "vision_rope_theta": 10000
}
Sources3

Direct evidence

Each position hashes its 2-, 3- and 4-gram of normalised token ids, each modulo eight primes, into row indices of each Engram layer’s table; an n-gram does not reach across the start of the sequence or an image position.

engram-hash · deepseek-ai/DeepSeek-V4.1-Flash / inference/engram.py
Pinned revision 2cba9e42aa02 ↗ · lines 159–184

Read code excerpt
    @torch.inference_mode()
    def forward(self, input_ids: torch.Tensor, start_pos: int, token_mask: torch.Tensor | None = None) -> torch.Tensor:
        """token_mask: [B, L], False for tokens that take no part in an n-gram (image spans).
        Returns the hash ids, shaped [B, L, n_engram_layers, n_hash_cols]."""
        batch, seqlen = input_ids.shape
        compressed = self.token_map[input_ids]
        if token_mask is not None:
            compressed = torch.where(token_mask, compressed, self.DEAD)
        self.cache[:batch, start_pos : start_pos + seqlen] = compressed

        positions = torch.arange(start_pos, start_pos + seqlen, device=input_ids.device).expand(batch, seqlen)
        tokens, blocked = [], torch.zeros_like(positions, dtype=torch.bool)
        for shift in range(self.layout.max_ngram_size):
            source = self.cache[:batch].gather(1, (positions - shift).clamp_min(0))
            blocked = blocked | (positions < shift) | (source == self.DEAD)
            tokens.append(torch.where(blocked, self.pad_id, source))
        tokens = torch.stack(tokens, dim=-1)  # [B, L, max_ngram_size]

        # XOR the multiplied ids together one lookback at a time, so the running value after step i
        # is the hash of the (i+1)-gram; each lands in its own prime-sized bucket range
        products = tokens.unsqueeze(2) * self.multipliers  # [B, L, n_engram_layers, max_ngram_size]
        rolling, hashes = products[..., 0], []
        for i in range(1, self.layout.max_ngram_size):
            rolling = torch.bitwise_xor(rolling, products[..., i])
            hashes.append(rolling.unsqueeze(-1) % self.primes[:, i - 1])
        return torch.cat(hashes, dim=-1) + self.offsets

Direct evidence

Tokens are embedded and repeated into four streams; each layer, after an Engram step where it has one, reads and writes the streams; the last reading mix collapses them, then the final norm and the head.

transformer-forward · deepseek-ai/DeepSeek-V4.1-Flash / inference/model.py
Pinned revision 2cba9e42aa02 ↗ · lines 1241–1272

Read code excerpt
    @torch.inference_mode()
    def forward(
        self, input_ids: torch.Tensor, start_pos: int = 0, images=None, token_types: torch.Tensor | None = None
    ):
        """input_ids: [b, s], every entry a real token id -- generate.py only ever passes positions it
        has already filled, so the padding it uses internally never reaches here. token_types /
        images carry the VL inputs built by image_processor.prepare_vl_inputs; image spans must lie
        inside the first (start_pos 0) chunk."""
        image_mask = None if token_types is None else token_types >= 0  # TEXT is -1
        # image tokens take no part in an n-gram and get no engram contribution; text-only needs no mask
        engram_mask = None if image_mask is None else ~image_mask
        engram_hashes = self.engram_hash(input_ids, start_pos, engram_mask) if self.engram_hash is not None else None
        h = self.embed(input_ids)
        if images is not None:
            assert start_pos == 0, "image spans must be prefilled in a single chunk"
            self.merge_image_embeddings(images, h)
        # Expand to hc_mult copies for Hyper-Connections
        h = h.unsqueeze(2).repeat(1, 1, self.hc_mult, 1)
        main_hiddens = []
        pre_mix = make_identity_pre_mix(h, self.hc_mult)
        for i, layer in enumerate(self.layers):
            if layer.engram is not None:
                h = layer.engram(h, engram_hashes[:, :, layer.engram.layer_hash_index, :], engram_mask)
            # the MTP head reads the attention input of its target layers, not their output
            if i in self.target_layer_ids:
                main_hiddens.append(h.mean(dim=2))
            h, pre_mix = layer(h, start_pos, pre_mix, image_mask)
        h = layer.hc_pre(h, pre_mix)
        logits = self.head(self.norm(h))
        output_ids = sample(logits, self.temperature)
        main_hidden = torch.cat(main_hiddens, dim=-1) if main_hiddens else None
        return output_ids, logits, main_hidden

Direct evidence

The reference configuration: 40 layers of width 5,120, 64 heads of 512 features with a 64-feature rotary part, a 1,280-feature query latent, a grouped output of 8 groups at rank 1,024, a window of 128, the per-layer compression ratios and the two source lists, the indexer and its candidate stage, hyper-connections of 4 streams, 384 routed experts of which 6 are used with 1 shared, Engram before layers 1 and 14, and three DSpark blocks.

config · deepseek-ai/DeepSeek-V4.1-Flash / inference/config.json
Pinned revision 2cba9e42aa02 ↗ · lines 1–66

Read code excerpt
{
    "vocab_size": 129280,
    "dim": 5120,
    "moe_inter_dim": 2304,
    "n_layers": 40,
    "n_mtp_layers": 3,
    "dspark_block_size": 5,
    "dspark_noise_token_id": 128799,
    "dspark_target_layer_ids": [37, 38, 39],
    "dspark_markov_rank": 256,
    "dspark_n_routed_experts": 128,
    "dspark_n_activated_experts": 3,
    "n_heads": 64,
    "n_routed_experts": 384,
    "n_shared_experts": 1,
    "n_activated_experts": 6,
    "score_func": "sqrtsoftplus",
    "route_scale": 1.5,
    "swiglu_limit": 10.0,
    "q_lora_rank": 1280,
    "head_dim": 512,
    "rope_head_dim": 64,
    "norm_eps": 1e-20,
    "o_groups": 8,
    "o_lora_rank": 1024,
    "window_size": 128,
    "kv_source_layers": [2, 8, 14, 20],
    "index_source_layers": [2, 8, 14, 20, 24, 28, 32, 36],
    "original_seq_len": 65536,
    "rope_theta": 10000,
    "rope_factor": 16,
    "beta_fast": 32,
    "beta_slow": 1,
    "index_n_heads": 32,
    "index_head_dim": 128,
    "index_topk": 512,
    "candidate_source_layer": 20,
    "candidate_topk_blocks": 2048,
    "candidate_block_size": 8,
    "hc_mult": 4,
    "hc_sinkhorn_iters": 20,
    "hc_eps": 1e-06,
    "engram_layer_ids": [1, 14],
    "engram_vocab_size": 16000000,
    "engram_num_embeddings": [384006168, 384016682],
    "engram_max_ngram_size": 4,
    "engram_pad_id": 2,
    "engram_compressed_vocab_size": 99092,
    "dtype": "fp8",
    "expert_dtype": "fp4",
    "compress_rope_theta": 160000,
    "compress_ratios": [0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0],
    "vision_n_layers": 32,
    "vision_dim": 1024,
    "vision_n_heads": 16,
    "vision_inter_dim": 2816,
    "vision_patch_size": 14,
    "vision_downsample_ratio": 3,
    "vision_max_n_token": 1024,
    "vision_min_pixels": 295936,
    "vision_max_wh_ratio": null,
    "image_token_id": 129264,
    "engram_n_heads": 8,
    "engram_head_dim": 256,
    "vision_rope_theta": 10000
}