# Praxis Gemini Engine > Reference for the Gemini / Antigravity engine path in Praxis. Auto-loads when an agent is touching Gemini, Antigravity, `@ai-sdk/google`, `direct.google`, `google-antigravity`, `GEMINI_API_KEY`, `GOOGLE_GENERATIVE_AI_API_KEY`, or considering a new engine adapter for Google models. Captures the policy + technical constraints found in `docs/research/gemini-subscription-engine.md` (2026-05-19) so future agents don't re-discover them. Use when this capability is needed. - Skill: `tomevault-io/praxis-gemini-engine` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/praxis-gemini-engine` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/praxis-gemini-engine/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/praxis-gemini-engine --- # Praxis Gemini engine — quick reference Praxis ships Gemini support today through the **Direct engine** family (`direct.google`), backed by Vercel `@ai-sdk/google` v6. There is **no subscription-tier (Google AI Pro / Ultra) engine** and there is a specific reason not to add one — read the policy section before designing anything. ## TL;DR for design decisions | Want | Build path | Status | |---------------------------------------|-----------------------------------------------------------------------------|-------------------------| | Gemini via API key (per-token billing)| `direct.google` (already shipped) | ✅ Available | | Google's official MCP-native loop | New `antigravity` engine wrapping the Python `google-antigravity` SDK | ⚠️ Possible, API-key only | | Pro/Ultra subscription billing | Subprocess the Antigravity CLI with the user's OAuth | ❌ **ToS violation** | ## Policy landmines ### Subscription-OAuth proxying is off-policy Google's abuse-mitigation policy (Feb 2026, effective **2026-03-25**) explicitly calls out "using Gemini CLI oAuth with third-party software" as a target for "more robust detection" — see `google-gemini/gemini-cli#22970`. Third-party plugins that proxy the OAuth token (e.g. `opencode-google-antigravity-auth`) have been linked to user account bans and shadow-bans in the wild. **Do not** build a Praxis engine that subprocesses the Antigravity CLI and inherits a user's Google Sign-In session. The asymmetric risk (user loses their Google account) is not worth the per-token savings, and we have no public ToS carve-out to point to that says otherwise. ### Gemini CLI sunset `gemini-cli` stops serving Pro/Ultra subscription traffic on **2026-06-18**; Antigravity CLI is the successor for that market. Both ride the same subscription policy — there is no Gemini path that gives a third-party app subscription-paid traffic today. ## The shipped path: `direct.google` `packages/engines/src/direct/providers.ts:10` declares the provider map; the Google branch is API-key only: ```ts import { google } from "@ai-sdk/google"; case "google": return google(modelId); // reads GOOGLE_GENERATIVE_AI_API_KEY ``` `packages/engines/src/direct/adapter.ts:104` then runs the standard `streamText` + `toVercelTools` loop — same code path as OpenAI / Anthropic / Ollama under `direct.*`. ### Selecting Gemini - `EngineConfig.engineId = "direct.google"` - `EngineConfig.model` overrides the default. Current model status: - **`gemini-3.5-flash`** — GA 2026-05-19 (I/O 2026). **Default in `providers.ts`.** Outperforms 3.1 Pro on Terminal-Bench 2.1 / GDPval-AA / MCP Atlas, ~4× faster than other frontier models. - **`gemini-3.5-pro`** — Ships June 2026. Listed in the vision allow-list for forward-compat; users can opt in via `EngineConfig.model` the day it lands. - **`gemini-3.1-pro-preview`** — GA despite the `-preview` suffix (Feb 2026 release). Recommended Pro tier until `gemini-3.5-pro` lands. - **`gemini-3-pro-preview`** — DISCONTINUED 2026-03-26. Do not add to allow-lists. - Older `gemini-2.5-*` / `gemini-2.0-*` / `gemini-1.5-*` remain in the allow-list for backward compat with persisted user configs. - Env: `GOOGLE_GENERATIVE_AI_API_KEY` set in the Praxis process before `createEngine`. - Allow-list + default-vision-model SSOT: `packages/core/src/config/vision-models.ts`. The substring regex `/gemini-\d+\.\d+-(pro|flash|ultra)/i` is the forward-compat fallback that admits unreleased `gemini-X.Y-(pro|flash|ultra)` variants without an SSOT edit. ### Caveats - `@ai-sdk/google` schema is a subset of OpenAPI 3.0 — **no union types** in tool args. Current Praxis tool schemas are fine; check if you add a new one with `z.union(...)` at the top level. - For Gemma models the provider auto-prepends system instructions to user messages (Gemma has no native system slot). Affects Gemma only. - `structuredOutputs: false` can be passed if a Zod schema trips the OpenAPI-subset constraint. ## If/when an Antigravity-SDK engine is added The official SDK (`pip install google-antigravity`, Apache 2.0) gives programmatic access to Google's internal agent harness with MCP support. Use API key, not OAuth. Pattern to mirror: - Sidecar Python subprocess (analogous to `packages/claude-cli-sdk` for Claude Code) — Node speaks JSON over stdio. - Map the SDK's event stream → `EngineEvent` in `packages/engines/src/antigravity/events.ts` (follow the `sdk-event-mapping` and `async-generator-event-stream` patterns). - Tool dispatch goes through the existing `packages/engines/src/mcp/tool-bridge.ts` — Antigravity SDK supports MCP, so no changes to the bridge are needed. - Add `"antigravity"` to `EngineId` and wire it in `factory.ts:19`. **Packaging cost**: Praxis is currently pure Node/Electron. An Antigravity-SDK engine adds a Python runtime requirement to the desktop bundle. Don't pay this cost speculatively — wait for concrete evidence that Google's agent loop outperforms Vercel's for a Praxis tutoring use case. ## Reload triggers Re-evaluate this skill if any of the following change: 1. Google publishes an **official Node/TypeScript Antigravity SDK** (today only Python is official; `Kanezal/antigravity-sdk` on npm is third-party). 2. Google publishes a **written ToS carve-out** allowing third-party apps to use a user's Pro/Ultra subscription via OAuth. 3. Antigravity CLI documents a **stream-JSON / non-interactive output mode** that makes subprocess driving viable. 4. The Antigravity Python SDK adds a non-API-key auth path. Until then, the recommendation stands: ship Gemini via `direct.google`, do not build an Antigravity-CLI subscription engine. ## References - `docs/research/gemini-subscription-engine.md` — full research write-up. - `packages/engines/src/direct/providers.ts` — provider map. - `packages/engines/src/direct/adapter.ts` — Direct engine session loop. - `packages/engines/src/factory.ts` — engine-id dispatch. - [@ai-sdk/google provider](https://ai-sdk.dev/providers/ai-sdk-providers/google-generative-ai) - [Gemini CLI Discussion #22970](https://github.com/google-gemini/gemini-cli/discussions/22970) - [google-antigravity/antigravity-sdk-python](https://github.com/google-antigravity/antigravity-sdk-python) --- > Source: [nklisch/praxis](https://github.com/nklisch/praxis) — distributed by [TomeVault](https://tomevault.io).