Gemini Interactions API Breaking Changes (May–June 2026): steps, response_format, streaming

Google is rolling out breaking changes to the Gemini Interactions API (v1beta) to support upcoming capabilities like mid-flight steering and asynchronous tool calls.

This update impacts:

• How responses are structured (outputs → steps)
• How output formats are requested (response_mime_type → response_format)
• Streaming event types (new interaction.* and step.* events)

Official migration guide: https://ai.google.dev/gemini-api/docs/interactions-breaking-changes-may-2026

What’s changing

1) outputs is replaced by steps

Instead of reading a flat outputs array, responses now come back as a structured steps timeline.

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

If you maintain stateless conversation history by feeding prior model responses back into the next request, you now need to collect and pass the steps array, appending the next user turn as a user_input step.

2) Output format changes: response_format

Google is consolidating output controls into a polymorphic response_format field:

• response_mime_type is removed.
• image_config is removed from generation_config and moved into response_format.
• response_format can be either a single object or an array (to request multiple modalities).

Each entry has a type discriminator such as:

• text
• audio
• image

3) Streaming event changes

Streaming clients need to update which events they listen for.

New event types include:

• interaction.created, interaction.in_progress, interaction.requires_action, interaction.completed, interaction.error
• step.start, step.delta, step.stop

Legacy event types are deprecated (for example interaction.start → interaction.created, and content.delta → step.delta).

If you stream function calls, step.delta can deliver partial JSON argument strings (arguments_delta) that you must accumulate.

Key dates (plan your migration)

According to Google’s guide:

• May 7, 2026: opt-in begins (REST users can opt in with Api-Revision: 2026-05-20).
• May 26, 2026: the new schema becomes the default (temporary opt-out header Api-Revision: 2026-05-07 available until June 8).
• June 8, 2026: legacy schema is removed; older SDK 1.x.x clients break for Interactions calls.

What to do now

1. Upgrade SDKs if you use the official client libraries.

• Python: >= 2.0.0
• JavaScript: >= 2.0.0

2. Update your code to:

• Read response content from steps instead of outputs
• Handle both user_input and model_output step types
• Switch from response_mime_type to response_format
• Update streaming listeners to the new interaction.* and step.* events

Why this matters for teams shipping AI features

If you’ve built product logic around Interactions streaming (tool calling, event ingestion, stateless history replay), this update can break production clients.

The safest approach is to opt in early (where possible), update parsing and streaming logic, and test before the May 26 default flip.

Sources:

• Google AI for Developers: https://ai.google.dev/gemini-api/docs/interactions-breaking-changes-may-2026