Tackling Inevitable I/O Latency in Rails

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February 6, 2026

Lessons from Kaigi on Rails 2025 on SSE and Async

Modern Rails applications increasingly depend on external systems: third-party APIs, background services, data pipelines, and—more recently—AI and LLM inference. While Rails itself continues to evolve in performance and concurrency, I/O latency remains largely unavoidable in many real-world scenarios.

At Kaigi on Rails 2025 , a Japanese conference dedicated to deep, production-level Rails topics, Taiki Kawakami (moznion) presented a session titled:

“Tackling Inevitable I/O Latency in Rails Apps with SSE and the async gem”

The talk addressed a practical and often under-discussed question: When latency cannot be eliminated, how can Rails applications remain responsive and trustworthy from the user’s perspective?

This article summarizes the core ideas of the session and expands on them with illustrative Rails examples , inspired by the architectural patterns discussed during the talk.