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A stream is a continuous flow of money between two wallets, denominated in a rate per unit time. Unlike transfers, which are discrete events, streams accrue value every second. Streams are ideal for:
  • Payroll / contractor pay — the recipient withdraws earned balance on their own schedule
  • Subscriptions — cancel any moment, get refunded for unused time
  • Service-tier SLAs — pay-per-millisecond for AI inference, compute, bandwidth
  • Agent-to-agent retainers — one agent pays another to keep availability

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Anatomy

┌─────────────────┐
│ Sender wallet   │
│  (wrapped       │
│   funds)        │
└────────┬────────┘
         │ flows at rate
         ▼
┌─────────────────┐        ┌─────────────────┐
│ Stream          │──────▶ │ Recipient       │
│  • flow_rate    │        │  balance        │
│  • buffer       │        │  (withdrawable) │
│  • runway       │        └─────────────────┘
└─────────────────┘
Key numbers on every stream:
  • flow_rate — amount per second (e.g. "0.00005" USDC = 0.00005/s≈0.00005/s ≈ 4.32/day)
  • wrapped_balance — sender’s locked-up funds powering the stream
  • buffer — reserved slack to prevent accidental underrun
  • runway_seconds — time until the wrapped balance runs out at current flow rate
  • recipient_balance — accrued, withdrawable by the recipient

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Create a stream

curl -X POST https://sandbox.getsly.ai/v1/streams \
  -H "Authorization: Bearer pk_test_..." \
  -H "Content-Type: application/json" \
  -d '{
    "from_wallet_id": "wal_sender_...",
    "to_wallet_id": "wal_recipient_...",
    "flow_rate": "0.00005",
    "currency": "USDC",
    "initial_deposit": "1000.00",
    "buffer": "50.00"
  }'
This locks 1000intothestream,startsflowingat1000 into the stream, starts flowing at 0.00005/s, and keeps a 50buffer.Therecipientaccrues 50 buffer. The recipient accrues ~4.32/day and can withdraw at any point.

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Recipient withdraws

curl -X POST https://api.getsly.ai/v1/streams/str_.../withdraw \
  -H "Authorization: Bearer pk_live_..." \
  -d '{ "amount": "10.00" }'  # omit to withdraw all accrued
Withdrawal creates a stream_withdraw transfer into the recipient’s wallet.

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Top up or adjust

# Add more funds
curl -X POST /v1/streams/str_.../topup -d '{ "amount": "500.00" }'

# Change flow rate (reflective of new runway)
curl -X PATCH /v1/streams/str_... -d '{ "flow_rate": "0.0001" }'

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Pause and resume

curl -X POST /v1/streams/str_.../pause
curl -X POST /v1/streams/str_.../resume
Paused streams don’t accrue. Wrapped funds remain locked until cancellation.

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Cancel

curl -X POST /v1/streams/str_.../cancel
  • Accrued balance transfers to the recipient
  • Unused wrapped funds return to the sender
  • The stream record remains for audit

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Runway and alerts

When runway_seconds drops below a threshold, Sly fires a stream_alert webhook and pushes a stream_alert SSE event to any connected agents that manage the stream: 
{
  "event": "stream_alert",
  "severity": "warning",
  "stream_id": "str_...",
  "runway_seconds": 3600,
  "message": "Stream will exhaust in 1 hour"
}
Severity levels: warning (<24h), critical (<1h), exhausted (runway=0).

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Agent permissions

When an agent creates or manages a stream, their wallet policy grants them granular permissions:
  • streams:create — open new streams
  • streams:modify — change flow rate, topup
  • streams:pause — pause/resume
  • streams:terminate — cancel
See wallet policies for how to scope these.

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Why streams over periodic transfers

StreamBatch of transfers
GranularityPer-secondPer period (daily/weekly/monthly)
RefundsAutomatic (cancel returns unused)Manual (via refunds API)
Gas / feesPaid once on wrapPaid per transfer
Recipient cash flowContinuousLumpy
AuditabilityEvery second is on-ledgerPer-transfer
For anything ongoing, prefer a stream.