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Solar Mini 4: The Quick Start, And Where It Fits In Your Agent OS
Solar Mini 4 is a new compact AI model from Upstage, and for a two-week window you can run it free inside Hermes Agent on Nous Portal.
It has 35 billion parameters with only 3 billion active, so it's quick, and Artificial Analysis scores it 24 on its Intelligence Index.
I set it up on video, gave it a real research job, and it came back fast with sources and a useful summary.
Here's the quick start, the one setting that stops a free model billing you, and exactly where Solar Mini 4 belongs in an Agent OS workflow.
What Solar Mini 4 is
Solar Mini 4 is Upstage's compact mixture-of-experts model, built for agent work where speed and cost matter.
Upstage calls it a "cost-efficient compact model for agentic use", and that's the slot I tested it in.
Here's the spec sheet, checked against Upstage's console docs, OpenRouter and Artificial Analysis.
| Spec | Official figure | What it means in an Agent OS |
|---|---|---|
| Maker | Upstage, an AI lab from South Korea. | It's a new provider option next to the US and Chinese labs you already route to. |
| Size | 35B total parameters with 3B active, in a mixture-of-experts design. | Only a small slice runs per token, so replies come back fast. |
| Context window | 512K tokens on Upstage's docs, and 524,288 tokens on OpenRouter and Nous Portal. | An agent can read long reports, transcripts and logs in one pass. |
| Max output | Up to 128K tokens on Upstage. | It can write long answers, which also means it can run up a bill when you pay per token. |
| Languages | Korean, English and Japanese for input and output. | It's a cheap multilingual lane for drafts and checks. |
| Capabilities | Reasoning mode, tool calling, structured outputs and chat. | Hermes can use tools with it and get clean structured data back. |
| Release | 22 September 2026, with a February 2026 training cut-off. | It's brand new, so expect providers to tweak limits. |
| Weights | Proprietary, with no public download. | You reach it through an API or a hosted portal, not a local runner. |
| Intelligence | Artificial Analysis Intelligence Index score of 24. | It's well above most small models, but it's still below the frontier. |
In my video I rounded the context window to 500,000 tokens, and Upstage's official number is 512K, so that's the one to trust.
Artificial Analysis says it beats Qwen 3.6 35B by 6 points with the same 3B active parameters.
In the video I put it as scoring above models with ten times the active parameters, which is how the launch was framed.
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Where to get Solar Mini 4 for free
There are two free doors right now, and three paid ones.
| Route | Cost | Where it fits in my Agent OS |
|---|---|---|
Nous Portal free variant, upstage/solar-mini4:free | Free for a two-week window. | The Hermes profile I actually run day to day while the window is open. |
| Upstage Console Playground | Free, and Upstage says no API key is needed. | A quick taste test before I give it a profile. |
OpenRouter, upstage/solar-mini4 | $0.05 per million input tokens and $0.20 per million output tokens. | The paid fallback for setups that already route through OpenRouter. |
Upstage API, solar-mini4 | $0.10 in and $0.40 out per million tokens, with 70% off through 10 October (UTC) when I checked. | Production use straight from the maker. |
Nous Portal paid variant, upstage/solar-mini4 | $0.05 in and $0.20 out per million tokens. | Only after the free window closes, and never by accident. |
The Nous Portal door is the one that matters for an Agent OS, because it plugs straight into Hermes Agent.
The Playground is a browser chat, so it's handy for a first look but it can't run your agent jobs.
Solar Mini 4 quick start: running in Hermes in five steps
This is the fastest path I know from zero to a working Solar Mini 4 agent.
- First, sign in at portal.nousresearch.com/cloud, create a Hermes Cloud agent, open the model section, click "Free" and pick Upstage Solar Mini 4.
- Second, if you use Hermes Desktop instead, create a new profile and name it "solar mini 4".
- Third, in that profile choose Nous Portal as the provider, refresh the models list and pick Solar Mini 4 from the free models.
- Fourth, run
hermes dashboard, go to Models, click "Set main model", type "solar", choose Nous Portal and select the free variant. - Fifth, open a new chat, type "test" and confirm the session is live.
When I did this, the reply came back fast and told me the session was live with memory switched off.
The full click-by-click version, with every screen, is in my Solar Mini 4 Hermes setup guide.
The free-vs-paid trap that costs people money
Nous Portal lists Solar Mini 4 twice.
The free one has an ID ending in :free, and the paid one doesn't.
If you pick the paid one, nothing breaks, your agent just quietly starts billing you.
That's why the one thing I told everyone to do in the video is pick the free variant when you set the main model.
After you save, check the model ID once more, because the two names look almost identical.
How Solar Mini 4 fits an Agent OS workflow
Most people bolt a new model onto their stack and start sending it everything, and that's the old way.
In my Agent OS, every model gets a job based on what it's good at.
My strongest models handle planning, hard builds and anything a client will see.
A fast, cheap model like Solar Mini 4 handles the repetitive work in between.
That split is how you keep an always-on agent affordable without dropping quality where it counts.
Step one: give it its own profile
I keep one Hermes profile per model, so I can switch and test in two clicks.
In the Agent OS, I open the Hermes tab, pick the solar mini 4 profile and chat with Hermes on Solar Mini 4 directly.
The manage section in the Agent OS also opens the Hermes dashboard, so I can swap the main model without the terminal.
Step two: hand it the jobs that suit it
These are the lanes I'd give Solar Mini 4 inside an Agent OS.
- It's a good fit for a morning news scan, because it came back fast with a breakdown, sources and a "what stands out" section when I asked for seven days of AI automation news.
- It's a good fit for long-document summaries, because Upstage built it for long-context work with a 512K window.
- It's a good fit for first drafts of notes, emails and outlines that a stronger model or a person tidies later.
- It's a good fit for Korean, English and Japanese drafts, since Upstage supports all three.
- It's a reasonable fit for sorting and tagging jobs, because it supports tool calling and structured outputs.
Step three: keep it away from the jobs that don't
Artificial Analysis recorded just 1% for it on Terminal-Bench 4.0, so I wouldn't run terminal-heavy coding agents on it.
It's not frontier level, and it isn't close to Claude Opus 5.5 on hard reasoning.
Anything that pays, sends or deletes still needs a stronger model and a human check.
The other free models sitting next to Solar Mini 4
When I filtered Nous Portal by "Free", this is what I saw on the day I recorded.
| Free model I saw on Nous Portal | Maker |
|---|---|
| Solar Mini 4 | Upstage |
| Nemotron | NVIDIA |
| Laguna XS 2.1 | Poolside |
| Ling 3.1 Flash | inclusionAI |
| Ling 3.0 Flash | inclusionAI |
| Step 3.7 Flash | StepFun |
| LongCat 2.0 | Meituan |
The list rotates, so treat it as a snapshot.
I like having two or three of these as backup profiles, because free models get rate limited.
If Solar Mini 4 hits a limit, I switch the profile to another free model and keep the job moving.
Limits to plan around
Free models can get rate limited, so build your workflow to fall back to another profile.
If Solar Mini 4 is missing from your model list, refresh the list before assuming it's gone.
The Nous Portal free window is two weeks, so don't build a client promise around it staying free.
Artificial Analysis describes it as very verbose, using about 88,000 output tokens per Intelligence Index task, which matters once you pay per token.
The weights aren't released, so there's no offline version for a local Agent OS.
One viewer said it ran badly for them, and I take that seriously, because results depend on the task.
Test it on one real job of your own before you give it anything important.
My honest take on Solar Mini 4 in an Agent OS
Solar Mini 4 is fast, it's free right now, and it handles basic agentic tasks without fuss.
It isn't frontier level, so it shouldn't be the brain of your whole system.
As a second profile for news, summaries and drafts, it's one of the easiest free wins I've added this month.
If you want the whole Agent OS with Hermes profiles already wired, it lives inside the AI Profit Boardroom.
For more ways to run Hermes without a bill, my Hermes free forever guide covers the local route too.
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FAQ
What is Solar Mini 4?
Solar Mini 4 is a compact mixture-of-experts model from Upstage in South Korea, with 35 billion total and 3 billion active parameters, a 512K context window, and support for tool calling and structured outputs.
Is Solar Mini 4 free?
Yes, for now. Nous Portal offers a free variant for a two-week window inside Hermes Agent, and the Upstage Console Playground lets you chat with it without an API key.
How do I add Solar Mini 4 to Hermes Agent?
Create a Hermes Cloud agent at portal.nousresearch.com/cloud and pick it from the free models, or create a Hermes Desktop profile with Nous Portal as the provider. Then set it as the main model in the Hermes dashboard and choose the free variant.
What is the free-vs-paid Solar Mini 4 trap?
Nous Portal lists a free variant ending in :free and a paid variant at $0.05 per million input tokens and $0.20 per million output tokens. Pick the free one, because the paid one works the same and bills you.
What should I use Solar Mini 4 for in an Agent OS?
Use it for fast, repetitive jobs like news scans, long-document summaries, first drafts and multilingual drafts. Keep a stronger model for hard reasoning, coding and anything client-facing.
Can Solar Mini 4 run locally?
No. Upstage has not released the weights, so you reach it through Nous Portal, OpenRouter, the Upstage API or the Upstage Playground.
Final word on Solar Mini 4
Set up the free variant, give it one repetitive job, and keep your strongest model for the hard work.
That's the fastest way to find out whether Solar Mini 4 earns a permanent profile in your Agent OS.
About Julian
I'm Julian Goldie, an AI entrepreneur, SEO expert and the founder of the AI Profit Boardroom, which has 3,400+ members.
I help business owners scale with AI agents, automation and SEO.
My YouTube channel has 400,000+ subscribers, and I run Goldie Agency, a seven-figure SEO agency.
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