Product Updates

Gemini API Interactions breaking changes (May 2026): outputs → steps, new response_format, and migration timeline

Google’s Gemini API Interactions endpoint is changing its response schema (outputs → steps), consolidating output format controls into response_format, and updating streaming event names, with a May 26 default flip and a June 8 legacy sunset.

By AI Coding Tools Directory•2026-05-16•10 min read
Last reviewed: 2026-05-16
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Google published a migration guide for upcoming breaking changes to the Gemini API Interactions endpoint, including a response schema change from outputs to steps, plus a firm timeline for rollout. (https://ai.google.dev/gemini-api/docs/interactions-breaking-changes-may-2026)

1) Response schema: outputs → steps

Google says responses move from a flat outputs array to a structured steps array:

  • POST /interactions returns only output steps.
  • GET /interactions/{id} returns the full step timeline (including the initial user_input step).

(https://ai.google.dev/gemini-api/docs/interactions-breaking-changes-may-2026)

2) Output format changes: response_mime_type removed

Google says response_mime_type is removed and output control moves into a polymorphic response_format field.

The guide also notes that image output configuration previously under generation_config.image_config moves into a response_format entry with type: "image". (https://ai.google.dev/gemini-api/docs/interactions-breaking-changes-may-2026)

3) Streaming event names change

Google’s guide lists new server-sent-event types (e.g. interaction.created, interaction.completed, step.start, step.delta, step.stop) replacing older event names. (https://ai.google.dev/gemini-api/docs/interactions-breaking-changes-may-2026)

For streaming function calls, Google says function arguments arrive as partial JSON string deltas (arguments_delta), and clients must accumulate deltas to reconstruct full arguments. (https://ai.google.dev/gemini-api/docs/interactions-breaking-changes-may-2026)

Migration timeline (key dates)

The guide lists a staged rollout:

Sources

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What is Gemini API Interactions breaking changes (May 2026): outputs → steps, new response_format, and migration timeline?
Google’s Gemini API Interactions endpoint is changing its response schema (outputs → steps), consolidating output format controls into response_format, and updating streaming event names, with a May 26 default flip and a June 8 legacy sunset.

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