systemPrompt field on session setup requests and
the systemPrompt session capability.
For protocol details, see v1 Session Setup
and v2 Session Setup.Announcements
Client-provided system prompts are stabilized
Clients can send system-level instructions on session setup in the stable ACP protocol surfaces.
Published: November 6, 2026
The Client-Provided System Prompt RFD has moved to
Completed, stabilizing the