Muse Spark Open 816B A42B

Meta Muse Spark Open

Quick answer: Meta Muse Spark Open is Meta Superintelligence Labs' open-weights 816B-total/42B-active MoE model (released October 15, 2026), scoring 89.2% MCP-Atlas, 89.0% GPQA Diamond, and 80.4% OSWorld Verified with a 1M-token context window. Released under the custom Muse Model License (source-available, revenue-threshold clause for Model-as-a-Service).

At a Glance

Where Muse Spark Open leads

• 89.2% MCP-Atlas tool-use accuracy, ahead of Nemotron 3 Ultra (63.1%), Beam (78.7%), and Inkling (76.0%)
• Strong agentic/OSWorld computer-use score (80.4% OSWorld Verified) — notably higher than any other model in its own comparison table except Kimi K3 (84.8%)
• 1M-token context, natively multimodal (text, image, video, audio input)

Where it lags

• Trails GLM 5.3 and Kimi K3 on GPQA Diamond (89.0% vs 91.7%/93.5%) and most coding sub-benchmarks (DeepSWE 1.1, SWE-Atlas-QnA, Terminal-Bench 2.1)
• Lower HLE/Omniscience knowledge scores relative to Qwen3.8 and GLM 5.3 on some cuts despite leading on AA Omniscience

Best for: teams that need open weights with strong agentic tool-use (MCP/OSWorld) rather than pure leaderboard-topping knowledge or coding scores.

What Muse Spark Open Is

Muse Spark Open is Meta Superintelligence Labs' open-weights release of its Muse Spark model family, an 816B-total/42B-active-parameter Mixture-of-Experts transformer (256 experts, top-8 routing) with a dedicated 1.8B-parameter perception encoder for image/video/audio input. It targets multi-step agentic reasoning, tool use, and coding-agent workflows, and ships with additional safety post-training intended for standalone deployment without an external guardrail layer.

It is distributed under the "Muse Model License" — permissive for most uses (modify, fine-tune, distill, redistribute) but requiring attribution ("Built with Muse Spark Open") and a separate agreement with Meta if a Model-as-a-Service deployment built on it exceeds $20M/year in aggregate revenue.

Weights are available in BF16 and NVFP4; NVFP4 needs ~700GB VRAM, BF16 ~2TB. Supported runtimes include SGLang, vLLM, Hugging Face Transformers, TensorRT-LLM, Unsloth, and llama.cpp (with an MLX path for dual Mac Studio M5 Ultra setups).

Specifications

Pricing

Open weights — free to download from Hugging Face (meta-models/Muse-Spark-Open-816B-A42B, gated access). No Meta-hosted API pricing published at release; third-party inference providers host it independently.

Context Window

Muse Spark Open has a 1,000,000-token context window at inference — roughly 1,500+ pages of text in a single request. Combined with its agentic training, this supports long-horizon multi-step tool-use workflows and large-codebase or long-document analysis.

Public Benchmark Scores

Scores above are reported by Meta's own model card and shown for context. They are not Benchgen measurements. Figures use xhigh reasoning effort, temperature=1.0, top_p=1.0, top_k=disabled — see the source for full methodology.

Excluded from the table above (bucket-C, documented per scout procedure):

• HLE-Diamond (no tools) — 26.1 and HLE (w/ tools) — 61.0: the vendor table reports two distinct HLE variants/conditions that do not clearly map to our existing generic humanitys-last-exam entity's methodology (tool-use condition and "Diamond" subset unconfirmed against our entity's task set) — excluded rather than guessed.
• Terminal-Bench 2.1 (Terminus 2 agent) — 76.4: our local entities are Terminal-Bench 3/4/Hard; no 2.1 entity exists and the version doesn't match an existing methodology — excluded.
• SimpleVQA (w/ tools) — 73.6: no matching local benchmark entity (checked docvqa, infovqa, mtvqa, pmc-vqa, worldvqa-forceanswer — none match); insufficient public methodology/task-count detail surfaced in this run to justify a new bucket-B config — excluded, flagged for follow-up.

Related Models & Benchmarks

• Compare: Kimi K3 · GLM 5.3
• Benchmarks: MCP-Atlas · GPQA Diamond · OSWorld Verified

Frequently Asked Questions

Specs and scores sourced from Meta's official Hugging Face model card. Last updated 2026-10-17.