# ContextOptions Builder for constructing a [`Context`](/documentation/BitcoinKernel/Context) — configure, then pass to [`init(options:)`](/documentation/BitcoinKernel/Context/init(options:)). ``` final class ContextOptions ``` ## Overview A one-shot builder: each setter replaces the previous value for that property. Defaults produce a mainnet context with no callbacks (see [`init(options:)`](/documentation/BitcoinKernel/Context/init(options:)) for the implications). Set the chain type first, attach callbacks, then build the context. > Warning: Not thread-safe. Configure on a single thread before creating > the context; the resulting ``doc://BitcoinKernel/documentation/BitcoinKernel/Context`` is thread-safe but building > `ContextOptions` concurrently is undefined. Wraps the opaque `btck_ContextOptions` type; `deinit` calls `btck_context_options_destroy` when the last Swift reference drops.