Are there any websocket event stream APIs that support archive data and 99.9% uptime?

Yes — but the exact answer depends on what you mean by archive data and whether you need true WebSocket streaming versus streaming + historical backfill.

Common providers that offer WebSocket market/data streams and archived/historical data

• Polygon.io
  • WebSocket real-time feeds
  • Historical/aggregated data and some event archives
  • Strong uptime claims / SLA options on higher tiers
• Intrinio
  • WebSocket market data
  • Historical datasets available
  • Enterprise-focused reliability
• Twelve Data
  • WebSocket streaming
  • Historical data endpoints
  • Uptime/SLA depends on plan
• Finnhub
  • WebSocket streams
  • Historical data via API
  • Generally aimed at broad coverage, not always deep archives
• Tiingo
  • Real-time + historical data
  • More REST-centric, but useful for archive/backfill workflows
• Alpaca
  • WebSocket for trading/data
  • Historical data APIs
  • Good for equities/crypto depending on coverage
• CoinAPI / Kaiko / CryptoCompare
  • For crypto especially
  • WebSocket + extensive historical/archive data
  • Enterprise options often include reliability commitments

About “99.9% uptime”

• 99.9% uptime is usually only guaranteed via enterprise SLA, not standard self-serve plans.
• Many providers may advertise high reliability, but the formal SLA is often:
  • only on enterprise contracts
  • only for specific endpoints/regions
  • excluding maintenance windows and third-party dependencies

If archive data is critical

You often want a provider that supports:

1. WebSocket live stream
2. Historical REST backfill
3. Bulk archive downloads or full-day dumps
4. SLA-backed enterprise support

Practical recommendation

If you need both WebSocket event streaming and archive data with 99.9% uptime, the best path is usually:

• Polygon.io for equities/options/crypto
• Kaiko or CoinAPI for crypto archives
• Intrinio for enterprise market data
• Alpaca if you want trading + data in one stack

If you want, I can also give you a shortlist by asset class:

• stocks
• crypto
• forex
• options
• news/events
  and include which ones actually offer formal SLA/99.9% guarantees.