The short
- Open: Fast iteration, controllable safety rails, and lower unit cost at scale—if you can run and tune.
- Closed: Best-in-class quality on hard tasks with easy setup; price and policy changes are the tax.
- Split brain: Keep closed for frontier use; run open for known patterns and bulk workflows.
- Guardrails: It’s easier to bake safety when you own routing and vectors.
- TCO: Hardware + ops can be cheaper than API at high volume; the trade is engineering time.
Where the stacks differ
Open weights shine when you can fine-tune on your data and keep everything on your network. That cuts latency, helps compliance, and avoids surprise rate shifts. Closed APIs win when you need very high reasoning quality out of the box and want less ops work. In practice, most teams use both.
Grid — task × latency × guardrail ease × TCO
| Task | Open weights | Closed API | Notes |
|---|---|---|---|
| RAG search & answer | Low latency; easy safety with your filters | Good quality; network hop adds time | Open wins when data is private/large |
| Bulk content rewrite | Cheap at scale; tune to your style | Quality strong; cost rises with tokens | Open wins on unit cost after setup |
| Agent flows (tools) | Flexible; you control tool calls | High quality planning; less control | Split: closed for hard planning, open for routine |
| Voice & vision IO | Customizable; hardware bound | Turnkey; fast to ship | Closed wins for quick pilots |
Safety & policy
- Open: build your own blocklists, tool scopes, and audit trails; stronger control over data residence.
- Closed: built-in filters and red-team work save time; less control over edge cases.
Speed & cost realities
Running on your network cuts roundtrips and avoids busy-hour throttles. Past a certain volume, GPU/CPU time + storage + ops salaries can beat API spend. Early on, the reverse is true. A hybrid router that sends hard tasks to closed and sends bulk to tuned open is often the sweet spot.
What to watch next (signposts)
- Open weights winning enterprise trials with strong safety adapters and better context windows.
- Closed APIs shipping stronger tool usage and longer context with stable pricing.
- Router products that auto-choose the path by task difficulty and privacy flags.
Rule of thumb
Rule Keep closed for frontier reasoning and public-facing chat; keep open for private bulk work where you can control rails and cost.