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Last verified: 2026-10-16
Muse Spark Open is Meta Superintelligence Labs’ frontier open-weight model, released October 15, 2026. It is a mixture-of-experts transformer with 816B total parameters and ~42B active per token, a 1 million-token context window, and native input for text, images, video, and audio. Meta trained it on real developer workflows — multi-file refactors, long debugging sessions, tool-calling scaffolds — and it leads the open-weight field on agentic coding and tool-use benchmarks. The number that matters for self-hosting is 226 GB. That is the 2-bit GGUF download, and it is why this model runs on a maxed-out Mac Studio rather than a datacenter cluster. The 4-bit build is 506 GB, and full BF16 is ~1.5 TB.
Already running this model? Register it with Tokios to reach it as https://api.tokios.com from any client.

Muse Spark Open at a glance

Sources: Meta’s Muse Spark Open blog post and the model card.

Variants and model ids

Unsloth publishes GGUF builds from 2-bit to 4-bit. Meta publishes BF16 and NVFP4 (Blackwell) checkpoints. The MLX community provides Apple Silicon-optimized quantizations.

GGUF (llama.cpp / Ollama-compatible)

GGUF source: unsloth/Muse-Spark-Open-816B-A42B-GGUF.

Full precision and Blackwell

MLX (Apple Silicon)

MLX source: mlx-community/Muse-Spark-Open-816B-A42B-oQ3e and -oQ4e.

MoE memory math

MoE has a memory trap: routing activates a fraction of parameters per token, but every expert weight stays resident. Muse Spark Open activates 42B of its 816B per token, but the full weight footprint is what you must load. The arithmetic:
  • 816B parameters × ~0.5 bytes at 4-bit ≈ 408 GB of weights
  • ~506 GB as shipped in UD-Q4_K_XL, once embeddings, the perception encoder, the audio encoder, and metadata are included
  • Add KV cache on top — at ~250 KB per token in BF16, a 131K context adds ~33 GB; the full 1M context adds ~266 GB
There is no way around the total-parameter memory cost. The practical path is aggressive quantization (2-bit at 226 GB for a Mac Studio, 4-bit at 506 GB for a multi-GPU box) or NVFP4 on Blackwell. See MoE routing and expert parallelism for how the architecture works and memory and offloading for what changes once weights spill past the GPU.

Hardware fit

Verdicts assume the model is fully resident (no CPU offloading) at a modest context length. On a 512 GB Mac Studio the 2-bit GGUF fits with room for a moderate context. The 4-bit build at 506 GB leaves almost no headroom on a single 512 GB machine — plan for the context you actually need. For the sizing method, see what size model fits your GPU?.

Picked a model? Connect it

One authenticated endpoint at https://api.tokios.com — no inbound ports, about 5 minutes.

Run it — beginner to advanced

macOS / Linux
Windows
The server starts a web UI at localhost:9931 and an OpenAI-compatible endpoint. Swap the quantization tag to UD-IQ2_XXS for the 226 GB build on a 512 GB Mac. See llama.cpp remote access to reach it from another machine.

Sampling settings

Meta recommends temperature = 1.0, top_p = 1.0, and top_k disabled. The reasoning effort defaults to xhigh — lower it to high or medium for simpler tasks to save tokens. There is no way to turn reasoning off entirely; set it to low for the shortest path.

Capabilities

  • Controllable reasoning. Set the effort in the chat template with reasoning_effort="low" (or medium, high, xhigh). Higher settings spend more tokens reasoning before answering. The model uses a channel-based template: to=self for internal reasoning, to=user for the final answer.
  • Full multimodal input. Text, images, video, and audio all go in; text comes out. The perception encoder handles vision (1.8B-param ViT), and a separate convolutional pyramid handles audio at 24 kHz mono.
  • Agentic coding. Meta trained on real developer workflows: multi-file refactors, debugging sessions, tool-calling scaffolds. It leads open-weight models on MCP-Atlas (89.2), DeepSWE 1.1 (68), Terminal-Bench 2.1 (85.0), and Toolathlon Verified (76.5).
  • Native tool calling. The chat template supports structured tool calls with schema adherence. Use --tool-call-parser musespark1x in vLLM or the equivalent in your runtime.
  • Multilingual. 100+ languages.

Benchmarks

Meta-reported at xhigh reasoning effort, on a model released October 15, 2026. No independent reproduction exists yet — treat these as the vendor’s claims until third-party evaluations appear.

Connect it with Tokios

A frontier model on dedicated hardware is one you want to reach from anywhere without exposing ports. Tokios sits after your runtime: it does not download the model or replace vLLM.
1

Keep your local runtime running

Start Muse Spark Open in vLLM, SGLang, llama.cpp, or Transformers and leave it bound to loopback (or your internal network).
2

Pair the Tokios connector

Sign in at tokios.com/console, open the Setup tab, and click Start pairing to get a one-time claim code (TKS-XXXX-XXXX). Run the installer on the machine that runs the model:
Windows
macOS
Linux
Then approve the device on the Setup or Connectors tab.
3

Register a deployment

In the Models tab, register the upstream model id (for example meta-models/Muse-Spark-Open-816B-A42B) under a public deployment name like muse-spark. Clients send the deployment name in the model field, never the local id — so re-quantizing later changes nothing on the client side.
4

Create an API key

In the Keys tab, click Create key. Copy the sk-tok-… key now — it is shown only once.

Call it from anywhere

Caveats

  • This is not a consumer-GPU model. The smallest usable quantization (2-bit at 226 GB) requires a 512 GB Mac Studio or equivalent. The recommended 4-bit build needs 506 GB. Plan your hardware before downloading.
  • Benchmarks are vendor-reported. Meta published them on release day. Wait for independent evaluations before treating the coding scores as settled.
  • The license is not Apache 2.0. Muse Spark Open ships under the Muse Model License, which differs from the Apache 2.0 license on Muse Glimmer. Read the license yourself before building on it.
  • No Ollama support yet. As of release day, Ollama has not published a Muse Spark Open tag. Use llama.cpp GGUF builds directly, vLLM, SGLang, or MLX.
  • 1M context is a ceiling, not a target. The KV cache at full context is ~266 GB in BF16 — that is on top of the model weights. Size your context to what you actually need.
  • Multimodal input depends on your runtime. Tokios passes image, video, and audio content through to the upstream endpoint — it does not add capabilities your runtime or quantization lacks. Check supported backends.
  • Reasoning cannot be turned off. The lowest setting is low, which still spends tokens on internal reasoning. For the shortest possible responses, use low and accept the overhead.

FAQ

The smallest usable build is the 2-bit GGUF at 226 GB, which runs on a Mac Studio M3/M5 Ultra with 512 GB of unified memory. The recommended 4-bit GGUF is 506 GB. NVFP4 needs ~700 GB (a single B200 node). Full BF16 is ~1.5 TB across 4 nodes of 8× H200 GPUs. The transparent calculation: 816B parameters × ~0.5 bytes at 4-bit ≈ 408 GB of weights, plus the perception encoder, audio encoder, embeddings, and overhead.
No. Even the most aggressive 2-bit quantization at 226 GB exceeds any single GPU’s memory. The practical single-machine paths are a 512 GB Mac Studio (GGUF Q2 via llama.cpp) or an 8× GPU workstation (GGUF Q4 or NVFP4). See what size model fits your GPU? for sizing math.
The weights are published under the Muse Model License, which is not Apache 2.0 or MIT. That differs from Muse Glimmer, which ships under Apache 2.0. Open weights and open source are not the same thing — the training data and pipeline are not released. Read the license yourself before building on it.
Muse Glimmer is a dense 30B model that fits a single 24 GB GPU, distilled from the Muse Spark teacher. Muse Spark Open is the teacher itself — 816B total, 42B active, MoE, 1M context, multimodal (text/image/video/audio). Glimmer is for consumer hardware; Spark Open is for workstation and server-class hardware. They share the Muse architecture lineage but differ in scale, capability, and hardware requirements.
Not yet. As of the October 15, 2026 release, Ollama has not published a Muse Spark Open tag. Use llama.cpp GGUF builds directly (llama serve -hf unsloth/Muse-Spark-Open-816B-A42B-GGUF:UD-Q4_K_XL), vLLM, SGLang, or MLX. Ollama support may follow — check ollama.com/library for updates.
Set reasoning_effort to low, medium, high, or xhigh (default) in the chat template or API call. Higher settings spend more tokens reasoning before answering. There is no way to turn reasoning off entirely — low is the minimum. This also passes through Tokios — set it in the API call parameters.
Meta’s own benchmarks compare it against Kimi K3, GLM 5.3, Qwen3.8, and others, and favour Muse Spark Open on most agentic and coding tasks. But those are vendor-run numbers on release day. All of these models require serious hardware (multi-GPU or 512 GB+ unified memory), so the practical answer is to serve each one and test your actual workload — see Kimi, GLM, and Qwen3.8.
Meta documents LoRA fine-tuning on attention layers only (experts remain frozen), but it requires 64 GPUs (8 nodes × 8× H100). The training config uses FSDP with expert parallelism. See the model card for the full fine-tuning recipe and the DistributedConfig setup.

Muse Glimmer

The dense 30B sibling that fits a single 24 GB GPU — same Muse lineage, consumer hardware.

MoE routing and expert parallelism

How mixture-of-experts models route tokens and how to parallelize across GPUs.

Coding agents with local models

Point Claude Code, Cline, or Aider at a model you host.

What fits your GPU?

Size the model and context to your VRAM or unified memory.

Llama 4

Meta’s other open-weight line, and why 17B active still needs 67 GB.

Quickstart

Pair a connector and register your first model end to end.