Muse Spark 1.3 - A Review

In this post I'll talk about my brief experience with muse , Meta's LLM harness for developers, as well as Muse Spark 1.3, their latest frontier-level model. The Bad I'll start with the bad, just because I like to end with the positive :) Skill Usage It's not that good following skills. If the skill has disable-model-invocation , sometimes it refuses to launch it, even if you manually call it. I think it happens when you call the skill mid-sentence, but it's not consistent. It's also not as good as other models at following skill instructions. It seems to get confused more often. For example, I have one skill that will address an issue from GitHub to PR. In Claude (Opus 5) and Cursor (Grok 4.6) it works perfectly. The first step is grilling the issue, after that's finished, the next step is autonomous, plan, implement with TDD, review and open PR. With Muse Spark 1.3, sometimes the skill will not continue and I have to nudge it for the next step, just saying something like "continue" is enough, but surely is annoying. Formatting The output is not great. Sometimes it will show me raw markdown, sometimes not. It's not consistent. Sandbox Having a sandbox is good, but in this case, it's a bit too restrictive. For example, I'm working with a Firebase project and I want to use the emulators. Well, too bad. The sandbox doesn't allow you to run files outside your workspace or use external ports. That would be great if I could add exceptions or some kind of configuration, but you can't. You are basically forced into --yolo mode if you don't want to be prompted on repeat for the same things over and over. What's sad is that even if you want to give them access, the models will just get stuck asking for permissions for the same thing over and over again and eventually they will just be stuck doing nothing. The Good Not everything is bad, of course. With a bit of effort I think it's actually quite usable. Price The main reason I decided to try the model. The subscription plan