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antigravity / gemini adapter - Google CLI (dual-binary)

Bernstein's adapter for the Google CLI. The upstream CLI is changing binary names ahead of a deprecation date: the legacy gemini binary stops serving free / AI Pro / Ultra subscribers on 2026-06-18, and the replacement antigravity binary carries the same model set and the same --output-format semantics forward. Enterprise customers on Standard or Enterprise licenses retain the legacy binary via paid Gemini Enterprise Agent Platform API keys.

The adapter is dual-binary aware. At spawn time it discovers which binary is on PATH and uses whichever the operator has installed. The adapter contract (flags passed, env-isolation allow-list, sandbox profile, network policy, rate-limit meter) is identical on either binary; only the discovered binary name and the discovery step differ.

The same adapter is registered under two registry keys:

  • gemini - back-compat for existing routines and operator muscle memory.
  • antigravity - so bernstein adapters check antigravity and bernstein run --cli antigravity ... work the moment the new binary is on PATH.

Discovery cascade

The cascade is deterministic and runs every time the adapter spawns:

  1. Operator override. If BERNSTEIN_GEMINI_BINARY is set and non-empty, that binary is used. If it does not resolve on PATH the adapter raises BinaryNotInstalledError and exits.
  2. Prefer the new binary. antigravity is checked next. If it resolves on PATH, it is used.
  3. Fall back to the legacy binary. gemini is checked. If it resolves on PATH, it is used (operator on the transition path who has not migrated yet, or an Enterprise license holder).
  4. Hard error. If none of the above resolves, the adapter raises BinaryNotInstalledError with a message naming both expected binaries and the override env var.

The cascade is implemented in bernstein.adapters.gemini.resolve_google_cli_binary and is covered by tests/unit/test_adapter_gemini.py::TestBinaryDiscoveryCascade.

Install paths

2026-06-18)

The Antigravity CLI is a Go binary distributed via an upstream installer. Follow the official transition notice for the current install command for your platform:

After installing, run antigravity auth to populate the system keyring; on a headless / SSH host the CLI falls back to a URL flow.

Operator note. Bernstein does not ship any installer URL inside the package. Operators install the binary from the upstream installer of their choice and Bernstein discovers whatever is on PATH.

gemini (legacy; Enterprise-only since 2026-06-18)

npm install -g @google/gemini-cli
gemini auth

The legacy binary keeps working for operators on Enterprise licenses with paid Gemini Enterprise Agent Platform API keys. Free / AI Pro / Ultra subscribers needed to migrate to antigravity by 2026-06-18; that deadline has now passed.

Operator override

For non-default install paths (vendored binary, pre-release build, shadow install under a custom name) set BERNSTEIN_GEMINI_BINARY:

export BERNSTEIN_GEMINI_BINARY=/opt/google/antigravity/bin/antigravity
bernstein adapters check antigravity

The override accepts either an absolute path or a bare binary name that resolves on PATH. Blank / whitespace-only values are treated as unset.

Verifying the install

# Confirm the binary is discoverable.
bernstein adapters check antigravity

# When only the legacy binary is on PATH this still reports useful
# information for the operator, even though the registry key is the
# new name.
bernstein adapters check gemini

A passing row shows the binary path, the captured --version line, and conformance: ok (meaning --help advertised every flag the adapter relies on: -p, -m, --output-format, --yolo).

Models

The model set is identical on either binary:

Model Notes
gemini-3.1-pro Highest reasoning.
gemini-3-flash Default in the Gemini app, Pro-grade reasoning at Flash speed.
gemini-3.1-flash-lite Cheapest tier.

No Anthropic models are available through this binary. Operators who want Claude continue using the existing claude adapter.

What is not changing

  • The adapter passes the same command line on either binary: -p, -m, --output-format, --yolo.
  • The env-isolation allow-list still scopes the spawned process to GOOGLE_API_KEY, GEMINI_API_KEY, GOOGLE_CLOUD_PROJECT, GOOGLE_APPLICATION_CREDENTIALS.
  • The rate-limit meter still labels upstream pressure under google_generative_language.
  • The strategy declaration in bernstein.adapters._contract.STRATEGY_MATRIX is identical for both registry keys: resume=UNSUPPORTED, dangerous_mode=CLI_FLAG, event_channel=STREAM_JSON.

Migration checklist

  1. Install antigravity from the upstream installer.
  2. Run antigravity auth to populate the system keyring.
  3. Run bernstein adapters check antigravity and confirm the row reports the binary path and conformance: ok.
  4. Optionally uninstall the legacy gemini binary. The adapter handles either ordering.

Successor CLI (agy)

The hosted backend behind the non-enterprise path was discontinued in June 2026. Consumer-path operators (free / AI Pro / Ultra) should use the separate agy adapter for the successor Antigravity CLI (agy binary). This dual-binary adapter remains the enterprise / API-key lane.