Google Ships antigravity-preview-09-2026 for Gemini Managed Agents with Files and Credentials APIs

Google released a new version of Gemini managed agents, antigravity-preview-09-2026, on 09-18, a major upgrade to the Gemini API's managed agent ecosystem. According to Google's Phil Schmid, the core of this update is cost efficiency plus two new interfaces: cache hit rates up to 22% higher, costs down by as much as 30%, and an 8% improvement in task completion in multi-turn coding scenarios.

Confirmed

• The new runtime antigravity-preview-09-2026 provides an updated agent harness whose tools and behavior are closer to Antigravity; Google AI Studio also has an official introduction (per m2)
• The runtime defaults to Gemini 3.8 Flash, and the default model is configurable
• The sandbox is a persistent Linux environment supporting bash execution and file tools
• Files API: handles data in and out of the agent sandbox; files.upload() can feed inline or upload files mid-conversation, and files.list() lists files
• Credentials API: register secrets once with credentials.create(), supporting bearertoken, environmentvariab… (post truncated) and other types; credentials are never exposed, and an egress proxy intercepts unauthorized requests to prevent key leakage

Why it matters

• The dual gains in cost and completion rate directly lower the barrier to building long-task agents, with clear benefits in multi-turn coding scenarios
• The Credentials API's security design (secrets never touch the app, egress proxy blocks unauthorized access) addresses the most sensitive credential-safety concern when agents connect to external APIs, and is worth referencing for similar agent platforms

Sources mainly come from Phil Schmid's (Google) series of posts (m1, m3, m4, m5), with details corroborating each other.

2026-09-18 ~ 2026-09-18 · 6 related posts

• [source] Google's Gemini managed agents update: 30% lower costs, new Files and Credentials APIs — _philschmid · 2026-09-18
• [source] Antigravity agent runtime upgrade: 30% cheaper multi-turn coding, 8% higher task completion — _philschmid · 2026-09-18
• Gemini Credentials API deep dive: zero plaintext secrets and egress-proxy exfiltration blocking — _philschmid · 2026-09-18
• Google adds Files API and secret-safe Credentials API to Gemini managed agents — _philschmid · 2026-09-18
• Google updates Gemini managed agents: new harness, Files API, managed credentials — osanseviero · 2026-09-18
• [source] Antigravity adds remote agent deploys, Files API and credential-safe OAuth — clmt · 2026-09-18