OpenAI Agents API: sandboxes can be pre-warmed, and compute is billed only during active turns

OpenAI's API changelog for October 9, 2026 (labelled v1/agents) lists two changes:

• An OpenAI-hosted sandbox can be pre-warmed before it is attached to an Agents API session. OpenAI says this cuts latency by creating and configuring the sandbox before the user finishes sending their message.
• OpenAI-hosted sandbox compute is now billed during active turns, so idle time between turns is no longer charged.