Solid Queue 1.6.0 ships with fiber-based workers, replacing the traditional thread-per-job model with cooperative multitasking. This is not a cosmetic change. Fibers let you run hundreds of concurrent jobs in a single OS thread, cutting memory overhead and context-switching costs. For agent workflows that spawn many lightweight tasks (API calls, LLM token streaming, webhook dispatches), this changes the economics of job orchestration.

Rails already had Active Job and Solid Queue for database-backed job queues. The new fiber mode integrates the Async gem, which provides non-blocking I/O primitives. Instead of blocking a thread while waiting for HTTP responses or database queries, a fiber yields control back to the scheduler.…