| Run admission latency | A run takes about 2.7 seconds to create. | Show a pending state and open the stream immediately. |
| Sandbox session latency | A sandbox-backed session takes about 2.5 seconds to create. | Create sessions before the user needs them when appropriate. |
| Coarse live-bus resync | One publisher failure can resync every subscriber on a session. | Handle stream.resync and replay durable events. |
| Strict tool output schema | One shared schema can reject valid operation-specific results. | Use oneOf or omit fields that do not apply. |
| MCP servers are not supported, 11 September 2026 | The mcp_servers field has been removed from the agent API. Nothing dispatched it, so it is no longer offered. Sending it is ignored, not rejected. | Use application tools. |
| The tools list does not restrict the sandbox, 11 September 2026 | An agent's tools list governs only Pantheon's four built-in tools. With requires_sandbox true the agent still has a shell and the file tools, and the sandbox reaches the network, so declaring no web tools does not remove web access. | Set requires_sandbox to false when the agent must not reach the shell or the network. |
| Billing: not available; the service is free during the builder preview; per-tenant rate limits apply, and billing is not planned yet. | No billing is available | Plan requests around per-tenant limits |
| Agent memory does not survive a session, 11 September 2026 | An agent's memory files live with the session sandbox, so they are lost when it is recycled. Durable cross-session memory is not switched on: the only rows in the durable store are copies of the stock template, one per scope. | Keep anything that must persist in your own application. See Agent memory. |
| OpenAPI prose gaps | Some new fields and routes have limited contract examples. | Use these guides with api/openapi/openapi.yaml and the smoke flow. |
| Claim fairness | A stuck older run can delay another tenant. | Use client timeouts and retry only safe requests. |
| Compensation claim race | Two workers can race expired-sandbox cleanup. | Treat cleanup errors as transient and inspect final session state. |
| Admission finalization race | A stale worker can race failure finalization. | Use terminal events as the final client state. |