Get the caller's credit balance

Returns the authenticated caller's spendable credit balance - the same number as credits.balance on GET /api/v1/me, without the identity and plan fields. Use it to check a key can afford a batch before starting one. The subject is always the credential holder; this endpoint accepts no user or owner id. balance is the caller's personal ledger; a call billed to an organization draws on a pool this number does not describe. Responses are never cacheable. Authenticate with an API key (b4m_live_) carrying any one of me:read, ai:chat, ai:generate or ai:decide, or a JWT.