OptionalafterOptionalappendText appended to the system prompt (whether default or overridden by
systemPrompt) during the initialize handshake. Use this to
inject additional instructions without losing the agent's built-in
prompt.
OptionalmodelAnthropic model identifier to select after initialization
(e.g. "claude-haiku-4-5", "claude-sonnet-4-5").
When provided, initialize() sends
a set_model control request immediately after the initialize
handshake completes.
OptionalonAsync teardown callback invoked by disconnect() (e.g. devbox shutdown).
OptionalonCalled when a non-critical error occurs (e.g. unparseable event,
listener exception). Defaults to console.error.
OptionalreplayWhen true, the connection queries the axon for the current head
sequence and replays all events up to that point without invoking
handlers. Unresolved permission/control requests are dispatched
to handlers after replay completes. Timeline events are emitted
for all replayed events regardless.
Set to false to replay the full history with handlers firing for
every event (legacy behavior).
Mutually exclusive with afterSequence.
OptionalsystemReplaces the default system prompt sent to Claude Code during the
initialize control handshake. When set, the agent uses only this
text as its system prompt — the built-in prompt is discarded entirely.
Mutually independent of appendSystemPrompt; if both are
provided, systemPrompt replaces the default and
appendSystemPrompt is appended to that replacement.
OptionalverboseWhen true, emit timestamped diagnostic logs to stderr for every
transport read/write and lifecycle event.
Useful during development; too noisy for production.
Axon sequence number to resume from. When set, the initial SSE subscription uses
{ after_sequence }so only events after this sequence are delivered — earlier events are skipped.Omit (or pass
undefined) to replay the full event history from the beginning of the Axon channel.Typical usage: persist
AxonEventView.sequencefrom a previous session and pass it here to avoid re-processing events you have already seen.Mutually exclusive with replay.