As of: 2026-10-16 12:39 CEST.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/p/2026-10-15-aiatmeta-muse-spark-open-launch/

# AI at Meta: 'Today we're releasing Muse Spark Open, the most capable US open-weight model to date'

AI at Meta (@AIatMeta), X, 2026-10-15.
Source: https://x.com/AIatMeta/status/2110779754274292212

## Why it matters

Official launch thread with the model specs (816B total / 42B active, 1M context, natively multimodal); ~767k views.

## Summary

Official launch thread: built for coding and agentic work; 816B total / 42B active parameters, 1M-token context, natively multimodal
across text, image, video and audio. A follow-up post says it is optimised to run on two Apple M5 Ultra Mac Studios with MLX and on
SGLang, vLLM, TensorRT-LLM, Transformers, llama.cpp and Unsloth (~83k views). ~767k views on the main post by Oct 16 morning.

## Archived text

> Today we’re releasing Muse Spark Open, the most capable US open-weight model to date.
> 
> Built for coding and agentic work, it excels at long-horizon tasks, complex software engineering, and multi-step reasoning.
> 
> Key Model Specs:
> → 816B total / 42B active parameters
> → 1M token context window
> → Natively multimodal across text, image, video, audio

Archived 2026-10-16 via fxtwitter (unofficial).
Counts: 783,808 views, 9,995 likes, 1,043 reposts, 378 replies (at fetch time)
Media: https://pbs.twimg.com/media/HUr8TsmbIAAT-m3.jpg?name=orig
Media: https://pbs.twimg.com/media/HUr8VZAbcAAF9yn.jpg?name=orig

## Cited in

- 2026-10-15: [Meta releases Muse Spark Open, an 816B open-weight model built with Apple to run on Mac Studios](https://postcutoff.com/e/2026-10-15-meta-muse-spark-open/)