Gemini's Interactions API default flips May 26 — your interaction.outputs reads will go undefined and tool calls silently stop

If your code calls Google's Gemini Interactions API (/v1beta/interactions), there is a short, silent window opening on May 26, 2026. On that date, Google flips the default response schema. interaction.outputs becomes interaction.steps, response_mime_type folds into a polymorphic response_format, image_config moves out of generation_config, and the streaming event names you wired listeners to all rename. The legacy schema still works if you explicitly send Api-Revision: 2026-05-07 — until June 8, 2026, when it's removed for good.

Most of these surfaces don't fail loudly. They fail by returning undefined, by ignoring a config field, or by emitting an SSE event your handler doesn't recognize. The first signal is usually a downstream consumer noticing that the model's reply is empty, or that the tool dispatch loop stopped firing, or that the generated image came back in the wrong aspect ratio.

The Timeline

May 7, 2026 — opt-in begins. New SDKs (Python ≥2.0.0, JS ≥2.0.0) ship; REST clients can opt in with Api-Revision: 2026-05-20.

May 26, 2026 — default flips. Any REST call without an Api-Revision header gets the new schema. SDKs older than 2.0.0 keep getting the legacy shape (for now).