ds4.c

ds4.c is a small native inference engine for DeepSeek V4 Flash. It is intentionally narrow: not a generic GGUF runner, not a wrapper around another runtime, and not a framework. The main path is a DeepSeek V4 Flash-specific Metal graph executor with DS4-specific loading, prompt rendering, KV state, and server API glue.

This project would not exist without llama.cpp and GGML, make sure to read the acknowledgements section, a big thank you to Georgi Gerganov and all the other contributors.

Now, back at this project. Why we believe DeepSeek v4 Flash to be a pretty special model deserving a stand alone engine? Because after comparing it with powerful smaller dense models, we can report that:

1. DeepSeek v4 Flash is faster because of less active parameters.
2. In thinking mode, if you avoid max thinking, it produces a thinking section that is a lot shorter than other models, even 1/5 of other models in many cases, and crucially, the thinking section length is proportional to the problem complexity. This makes DeepSeek v4 Flash usable with thinking enabled when other models are practically impossible to use in the same conditions.
3. The model features a context window of 1 million tokens.
4. Being so large, it knows more things if you go sampling at the edge of knowledge. For instance asking about Italian show or political questions soon uncovers that 284B parameters are a lot more than 27B or 35B parameters.
5. It writes much better English and Italian. It feels a quasi-frontier model.
6. The KV cache is incredibly compress, allowing long context inference on local computers and on disk KV cache persistence.
7. It works well with 2-bit quantization, if quantized in a special way (read later). This allows to run it in MacBooks with 128GB of RAM.
8. We expect DeepSeek to release updated versions of v4 Flash in the future, even better than the current one.

That said, a few important things about this project:

• The local inference landscape contains many excellent projects, but new models are released continuously, and the attention immediately gets captured by the next model to implement. This project takes a deliberately narrow bet: one model at a time, official-vector validation (logits obtained with the official implementation), long-context tests, and enough agent integration to know if it really works. The exact model may change as the landscape evolves, but the constraint remains: local inference credible on high end personal machines or Mac Studios, starting from 128GB of memory.
• This software is developed with strong assistance from GPT 5.5 and with humans leading the ideas, testing, and debugging. We say this openly because it shaped how the project was built. If you are not happy with AI-developed code, this software is not for you. The acknowledgement below is equally important: this would not exist without llama.cpp and GGML, largely written by hand.
• This implementation is based on the idea that compressed KV caches like the one of DeepSeek v4 and the fast SSD disks of modern MacBooks should change our idea that KV cache belongs to RAM. The KV cache It is actually a first class disk citizen.
• Our vision is that local inference should be a set of three things working well together, out of the box: A) inference engine with HTTP API + B) GGUF specially crafted to run well under a given engine and given assumptions + C) testing and validation with coding agents implementations. This inference engine only runs with the GGUF files provided. It gets tested against officially obtained logits at different context sizes. This project exists because we wanted to make one local model feel finished end to end, not just runnable. However this is just alpha quality code, so probably we are not still there.
• This is Metal-only, may implement CUDA support in the future? Perhaps, but nothing more. The CPU path is only for correctness check, but warning: current macOS versions have a bug in the virtual memory implementation that will crash the kernel if you try to run the CPU code. Remember? Software sucks. I was not possible to fix the CPU inference to avoid crashing, since each time there is to restart the computer, which is not funny. Help us, if you have the guts.

Acknowledgements to llama.cpp and GGML

ds4.c does not link against GGML, but it exists thanks to the path opened by the llama.cpp project and the kernels, quantization formats, GGUF ecosystem, and hard-won engineering knowledge developed there. We are thankful and indebted to llama.cpp and its contributors. Their implementation, kernels, tests, and design choices were an essential reference while building this DeepSeek V4 Flash-specific inference path. Some source-level pieces are retained or adapted here under the MIT license: GGUF quant layouts and tables, CPU quant/dot logic, and certain Metal kernels. For this reason, and because we are genuinely grateful, we keep the GGML authors copyright notice in our LICENSE file.

Model Weights

This implementation only works with the DeepSeek V4 Flash GGUFs published for this project. It is not a general GGUF loader, and arbitrary DeepSeek/GGUF files will not have the tensor layout, quantization mix, metadata, or optional MTP state expected by the engine. The 2 bit quantizations provided here are not a joke: they behave well, work under coding agents, call tools in a reliable way. The 2 bit quants use a very asymmetrical quantization: only the routed MoE experts are quantized, up/gate at IQ2_XXS, down at Q2_K. They are the majority of all the model space: the other components (shared experts, projections, routing) are left untouched to guarantee quality.

Download one main model:

./download_model.sh q2   # 128 GB RAM machines
./download_model.sh q4   # >= 256 GB RAM machines

The script downloads from https://huggingface.co/antirez/deepseek-v4-gguf, stores files under ./gguf/, resumes partial downloads with curl -C -, and updates ./ds4flash.gguf to point at the selected q2/q4 model. Authentication is optional for public downloads, but --token TOKEN, HF_TOKEN, or the local Hugging Face token cache are used when present.

./download_model.sh mtp fetches the optional speculative decoding support GGUF. It can be used with both q2 and q4, but must be enabled explicitly with --mtp. The current MTP/speculative decoding path is still experimental: it is correctness-gated and currently provides at most a slight speedup, not a meaningful generation-speed win.

Then build:

make

./ds4flash.gguf is the default model path used by both binaries. Pass -m to select another supported GGUF from ./gguf/. Run ./ds4 --help and ./ds4-server --help for the full flag list.

Speed

These are single-run Metal CLI numbers with --ctx 32768, --nothink, greedy decoding, and -n 256. The short prompt is a normal small Italian story prompt. The long prompts exercise chunked prefill plus long-context decode. Q4 requires the larger-memory machine class, so M3 Max Q4 numbers are N/A.

CLI

One-shot prompt:

./ds4 -p "Explain Redis streams in one paragraph."

No -p starts the interactive prompt:

./ds4
ds4>

The interactive CLI is a real multi-turn DS4 chat. It keeps the rendered chat transcript and the live Metal KV checkpoint, so each turn extends the previous conversation. Useful commands are /help, /think, /think-max, /nothink, /ctx N, /read FILE, and /quit. Ctrl+C interrupts the current generation and returns to ds4>.

The CLI defaults to thinking mode. Use /nothink or --nothink for direct answers. --mtp MTP.gguf --mtp-draft 2 enables the optional MTP speculative path; it is useful only for greedy decoding, currently uses a confidence gate (--mtp-margin) to avoid slow partial accepts, and should be treated as an experimental slight-speedup path.

Server

Start a local OpenAI/Anthropic-compatible server:

./ds4-server --ctx 100000 --kv-disk-dir /tmp/ds4-kv --kv-disk-space-mb 8192

The server is Metal-only. It keeps one mutable graph/KV checkpoint in memory, so stateless clients that resend a longer version of the same prompt can reuse the shared prefix instead of pre-filling from token zero.

Request parsing and sockets run in client threads, but inference itself is serialized through one Metal worker. The current server does not batch multiple independent requests together; concurrent requests wait their turn on the single live graph/session.

Supported endpoints:

• GET /v1/models
• GET /v1/models/deepseek-v4-flash
• POST /v1/chat/completions
• POST /v1/completions
• POST /v1/messages

/v1/chat/completions accepts the usual OpenAI-style messages, max_tokens/max_completion_tokens, temperature, top_p, top_k, min_p, seed, stream, stream_options.include_usage, tools, and tool_choice. Tool schemas are rendered into DeepSeek's DSML tool format, and generated DSML tool calls are mapped back to OpenAI tool calls.

/v1/messages is the Anthropic-compatible endpoint used by Claude Code style clients. It accepts system, messages, tools, tool_choice, max_tokens, temperature, top_p, top_k, stream, stop_sequences, and thinking controls. Tool uses are returned as Anthropic tool_use blocks.

Both APIs support SSE streaming. In thinking mode, reasoning is streamed in the native API shape instead of being mixed into final text.

Minimal OpenAI example:

curl http://127.0.0.1:8000/v1/chat/completions \
  -H 'Content-Type: application/json' \
  -d '{
    "model":"deepseek-v4-flash",
    "messages":[{"role":"user","content":"List three Redis design principles."}],
    "stream":true
  }'

Agent Client Usage

ds4-server can be used by local coding agents that speak OpenAI-compatible chat completions. Start the server first, and set the client context limit no higher than the --ctx value you started the server with:

./ds4-server --ctx 100000 --kv-disk-dir /tmp/ds4-kv --kv-disk-space-mb 8192

You can use larger context and larger cache if you wish. Full context of 1M tokens is going to use more or less 26GB of memory (compressed indexer alone will be like 22GB), so configure a context which makes sense in your system. With 128GB of RAM you would run the 2-bit quants, which are already 81GB, 26GB are going to be likely too much, so a context window of 100~300k tokens is wiser.

The 384000 output limit below avoids token caps since the model is able to generate very long replies otherwise (up to 384k tokens). The server still stops when the configured context window is full.

For opencode, add a provider and agent entry to ~/.config/opencode/opencode.json:

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "ds4": {
      "name": "ds4.c (local)",
      "npm": "@ai-sdk/openai-compatible",
      "options": {
        "baseURL": "http://127.0.0.1:8000/v1",
        "apiKey": "dsv4-local"
      },
      "models": {
        "deepseek-v4-flash": {
          "name": "DeepSeek V4 Flash (ds4.c local)",
          "limit": {
            "context": 100000,
            "output": 384000
          }
        }
      }
    }
  },
  "agent": {
    "ds4": {
      "description": "DeepSeek V4 Flash served by local ds4-server",
      "model": "ds4/deepseek-v4-flash",
      "temperature": 0
    }
  }
}

For Pi, add a provider to ~/.pi/agent/models.json:

{
  "providers": {
    "ds4": {
      "name": "ds4.c local",
      "baseUrl": "http://127.0.0.1:8000/v1",
      "api": "openai-completions",
      "apiKey": "dsv4-local",
      "compat": {
        "supportsStore": false,
        "supportsDeveloperRole": false,
        "supportsReasoningEffort": true,
        "supportsUsageInStreaming": true,
        "maxTokensField": "max_tokens",
        "supportsStrictMode": false,
        "thinkingFormat": "deepseek",
        "requiresReasoningContentOnAssistantMessages": true
      },
      "models": [
        {
          "id": "deepseek-v4-flash",
          "name": "DeepSeek V4 Flash (ds4.c local)",
          "reasoning": true,
          "thinkingLevelMap": {
            "off": null,
            "minimal": "low",
            "low": "low",
            "medium": "medium",
            "high": "high",
            "xhigh": "xhigh"
          },
          "input": ["text"],
          "contextWindow": 100000,
          "maxTokens": 384000,
          "cost": {
            "input": 0,
            "output": 0,
            "cacheRead": 0,
            "cacheWrite": 0
          }
        }
      ]
    }
  }
}

Optionally make it the default Pi model in ~/.pi/agent/settings.json:

{
  "defaultProvider": "ds4",
  "defaultModel": "deepseek-v4-flash"
}

For Claude Code, use the Anthropic-compatible endpoint. A wrapper like this matches the local ~/bin/claude-ds4 setup:

#!/bin/sh
unset ANTHROPIC_API_KEY

export ANTHROPIC_BASE_URL="${DS4_ANTHROPIC_BASE_URL:-http://127.0.0.1:8000}"
export ANTHROPIC_AUTH_TOKEN="${DS4_API_KEY:-dsv4-local}"
export ANTHROPIC_MODEL="deepseek-v4-flash"

export ANTHROPIC_CUSTOM_MODEL_OPTION="deepseek-v4-flash"
export ANTHROPIC_CUSTOM_MODEL_OPTION_NAME="DeepSeek V4 Flash local ds4"
export ANTHROPIC_CUSTOM_MODEL_OPTION_DESCRIPTION="ds4.c local GGUF"

export ANTHROPIC_DEFAULT_SONNET_MODEL="deepseek-v4-flash"
export ANTHROPIC_DEFAULT_HAIKU_MODEL="deepseek-v4-flash"
export ANTHROPIC_DEFAULT_OPUS_MODEL="deepseek-v4-flash"
export CLAUDE_CODE_SUBAGENT_MODEL="deepseek-v4-flash"

export CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1
export CLAUDE_CODE_DISABLE_NONSTREAMING_FALLBACK=1
export CLAUDE_STREAM_IDLE_TIMEOUT_MS=600000

exec "$HOME/.local/bin/claude" "$@"

Claude Code may send a large initial prompt, often around 25k tokens, before it starts doing useful work. Keep --kv-disk-dir enabled: after the first expensive prefill, the disk KV cache lets later continuations or restarted sessions reuse the saved prefix instead of processing the whole prompt again.

Thinking Modes

DeepSeek V4 Flash has distinct non-thinking, thinking, and Think Max modes. The server defaults to thinking mode. reasoning_effort=max requests Think Max, but it is only applied when the context size is large enough for the model card recommendation; smaller contexts fall back to normal thinking. OpenAI reasoning_effort=xhigh still maps to normal thinking, not Think Max.

For direct replies, use thinking: {"type":"disabled"}, think:false, or a non-thinking model alias such as deepseek-chat.

Disk KV Cache

Chat/completion APIs are stateless: agent clients usually resend the whole conversation every request. ds4-server handles this by comparing the rendered token stream with cached token prefixes. The live in-memory checkpoint covers the current session; the disk KV cache makes useful prefixes survive session switches and server restarts.

For RAM reasons there is currently only one live KV cache in memory. When a new unrelated session replaces it, the old checkpoint can only be resumed without re-processing if it was written to the disk KV cache. In other words, memory cache handles the active session; disk cache is the resume mechanism for different sessions.

Enable it with:

./ds4-server --kv-disk-dir /tmp/ds4-kv --kv-disk-space-mb 8192

The cache key is the SHA1 of exact token IDs, not raw text. Each token ID is hashed as a little-endian 32-bit integer, and files are named <sha1>.kv. The file is intentionally written with ordinary read/write I/O, not mmap, so restoring cache entries does not add more VM mappings to a process that already maps the model.

On disk, a cache file is:

KVC fixed header, 48 bytes
u32 rendered_text_bytes
rendered_text_bytes of UTF-8-ish token text
DS4 session payload, payload_bytes from the KVC header

The fixed header is little-endian:

0   u8[3]  magic = "KVC"
3   u8     version = 1
4   u8     routed expert quant bits, currently 2 or 4
5   u8     save reason: 0 unknown, 1 cold, 2 continued, 3 evict, 4 shutdown
6   u8[2]  reserved
8   u32    cached token count
12  u32    hit count
16  u32    context size the snapshot was written for
20  u8[4]  reserved
24  u64    creation Unix time
32  u64    last-used Unix time
40  u64    DS4 session payload byte count

The rendered text is the tokenizer-decoded text for the cached token prefix. It is stored only for observability, so humans can inspect a cache directory without decoding token IDs. It is not used as the key and it is not trusted when loading; after load, the stored checkpoint tokens must still match the incoming request prefix.

The DS4 session payload starts with thirteen little-endian u32 fields:

0   magic = "DSV4"
1   payload version = 1
2   saved context size
3   prefill chunk size
4   raw KV ring capacity
5   raw sliding-window length
6   compressed KV capacity
7   checkpoint token count
8   layer count
9   raw/head KV dimension
10  indexer head dimension
11  vocabulary size
12  live raw rows serialized below

Then it stores:

• u32[token_count] checkpoint token IDs.
• float32[vocab_size] logits for the next token after that checkpoint.
• u32[layer_count] compressed attention row counts.
• u32[layer_count] ratio-4 indexer row counts.
• For every layer: the live raw sliding-window KV rows, written in logical position order rather than physical ring order.
• For compressed layers: live compressed KV rows and compressor frontier tensors.
• For ratio-4 compressed layers: live indexer compressed rows and indexer frontier tensors.

The logits are raw IEEE-754 float32 values from the host ds4_session buffer. They are saved immediately after the checkpoint tokens so a loaded snapshot can sample or continue from the exact next-token distribution without running one extra decode step. MTP draft logits/state are not persisted; after loading a disk checkpoint the draft state is invalidated and rebuilt by normal generation.

The tensor payload is DS4-specific KV/session state, not a generic inference graph dump. It is expected to be portable only across compatible ds4.c builds for this model layout.

The cache stores checkpoints at four moments:

• cold: after a long first prompt reaches a stable prefix, before generation.
• continued: when prefill or generation advances the live conversation by the configured interval.
• evict: before an unrelated request replaces the live in-memory session.
• shutdown: when the server exits cleanly.

Cold saves intentionally trim a small token suffix and align down to a prefill chunk boundary. This avoids common BPE boundary retokenization misses when a future request appends text to the same prompt. The defaults are conservative: store prefixes of at least 512 tokens, cold-save prompts up to 30000 tokens, trim 32 tail tokens, and align to 2048-token chunks. The important knobs are:

• --kv-cache-min-tokens
• --kv-cache-cold-max-tokens
• --kv-cache-continued-interval-tokens
• --kv-cache-boundary-trim-tokens
• --kv-cache-boundary-align-tokens

By default, checkpoints may be reused across the 2-bit and 4-bit routed-expert variants if the token prefix matches. Use --kv-cache-reject-different-quant when you want strict same-quant reuse only.

The cache directory is disposable. If behavior looks suspicious, stop the server and remove it. You can investigate what is cached with hexdump as the kv cache files include the verbatim prompt cached.

Backends

The default backend is Metal:

./ds4 -p "Hello" --metal

There is also a CPU reference/debug path:

./ds4 -p "Hello" --cpu

Do not treat the CPU path as the production target. The server is Metal-only, and the optimized implementation lives in the Metal graph path. This may change in the future.

Test Vectors

tests/test-vectors contains short and long-context continuation vectors captured from the official DeepSeek V4 Flash API. The requests use deepseek-v4-flash, greedy decoding, thinking disabled, and the maximum top_logprobs slice exposed by the API. Local vectors are generated with ./ds4 --dump-logprobs and compared by token bytes, so tokenizer/template or attention regressions show up before they become long generation failures.

All project tests are driven by the C runner:

make test                  # ./ds4_test --all
./ds4_test --logprob-vectors
./ds4_test --server