Modal Launches Sticky Sessions to Solve State Continuity for Real-Time AI Apps
Modal introduces Sticky Sessions, enabling fixed routing of all requests within a session to the same container, supporting stateful applications like voice agents and multiplayer games.
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When building real-time AI applications such as speech-to-text models, conversational agents, or multiplayer games, developers face a core contradiction: traditional serverless computing assumes each request is independent to allow flexible scaling, but these applications require state continuity throughout a session, meaning users must return to the same processing container upon reconnection.
To address this pain point, cloud infrastructure company Modal launched the Sticky Sessions feature on October 19, 2026. Built on its low-latency Modal Servers, this feature ensures that all requests within the same session are routed to the same container. Developers can enable it by creating a server with the @modal.sessioned() decorator and starting sessions via SDK or HTTP API.
The core innovation of Sticky Sessions lies in using 'sessions' rather than 'requests' as the unit of concurrency for auto-scaling. This means the system automatically provisions new containers as active sessions increase and recycles them when sessions become idle. This mechanism avoids the previous anti-pattern of setting max_containers=1 to force stickiness at the cost of scalability, and also solves the issue where WebSocket disconnections could route to a new container, causing state loss.
For teams developing low-latency voice agents, shared chat rooms, or online games, this update provides first-class infrastructure support. It allows applications to maintain stable WebRTC signaling and continuous memory state while still benefiting from the pay-as-you-go and elastic scaling advantages of serverless architecture.