rivumi now has a Cloudflare Durable Object run resource with async creation, status/cancel/artifacts, live NDJSON, and Last-Event-ID SSE; remote approvals use a separate short-lived capability. Python also provides an attach client and a stateful conversation WebSocket. Production deployment, cross-runtime parity, and full multi-tenant hardening remain unverified.
Rivumi exposes bounded-run and conversation contracts through a typed 0.x SDK facade. WebSocket attach wraps one prebuilt, controller-owned runtime session rather than providing conversation-ID resume or multi-client routing.
Cartesia's core is Sonic real-time TTS, Ink STT, and streaming inference. Although it offers the Line voice-agent platform in 2026, buyers must still separate the model layer from telephony orchestration and design consent, retention, and fallback for cloned voices.
Ably manages global realtime connections, channels, presence, and short-window recovery; applications still own idempotency, durable business state, token capabilities, and offline resynchronization.
Durable Objects map a name or ID to a globally unique, single-threaded actor with private SQLite storage. They fit per-room, per-user, per-tenant, and per-run coordination boundaries; the real design question is where the object key belongs.
PartyKit concentrates WebSocket coordination in room-keyed stateful servers for multiplayer and presence, while durable documents, authorization, hibernation, and platform ownership still need explicit design.
Socket.IO is an event protocol and runtime over WebSocket or long-polling, not a native WebSocket compatibility layer; ordering, arrival, recovery, and horizontal scaling need separate designs.
WebSocket supplies a duplex message transport, not auth renewal, schemas, acknowledgements, replay, rooms, or backpressure policy; those layers determine production correctness.