Gemini's new agent harness adds Files and Credentials APIs
Google's antigravity-preview-09-2026 puts managed agents on Gemini 3.8 Flash, keeps secrets out of the sandbox, and bills no compute during preview.
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Your API keys never enter the sandbox
The new Credentials API stores your secrets and injects them as auth headers at request time through an egress proxy, so keys never live in the agent's ephemeral Linux box. Reference one by name — credential: "github-production" — and rotate it without touching your triggers, which finally lets an autonomous agent call third-party APIs without you handing over the keys.
Stream whole datasets straight into context
A new Files API pipes large datasets, media, and unstructured docs directly into an agent's working context, cutting the custom preprocessing pipeline you'd normally build first. It's reported alongside the harness update rather than spelled out in the core docs, so confirm size limits before you depend on it.
The harness jumps to Gemini 3.8 Flash
antigravity-preview-09-2026 swaps the old 3.5-Flash harness for Gemini 3.8 Flash, with Google claiming roughly 22% better context-cache hit rates on long, multi-step runs and about 9% on complex coding. Setup is still one call: a single request spins up an agent that reasons, runs code, and manages files in an isolated Linux sandbox.
Preview compute is free — for now
Billing is pay-as-you-go on the underlying Gemini tokens (Google estimates $0.25–$5.00 per task), but environment compute isn't charged during the preview and free-tier projects get a rate limit and quota. It's the cheapest window you'll get to prototype long-running agents before the meter switches on.