Google Antigravity 2.18.1–2.19.1 can't connect to the model behind HTTPS filtering: `unable to verify the first certificate` (fixed in 2.21.0)

Context

Source(s): https://discuss.ai.google.dev/t/ssl-certificate-error-since-antigravity-2-18-1-still-present-in-2-19-1/186729 Signal: 120 views; the original poster marked their own "fixed in 2.21.0" reply as the solution (October 2026). Status: reported working by source, not reproduced by us.

Problem

After updating to Antigravity 2.18.1 and reconnecting the Google account, Antigravity can't connect to the model and shows an SSL/TLS certificate verification (x509) error. The same machine and network worked on versions before 2.18.1, and 2.19.1 still had the error.

Error (redacted / normalized)

unable to verify the first certificate

Applies when

Antigravity 2.18.1 and 2.19.1, on a device whose HTTPS traffic goes through a content filter that inspects HTTPS (Netspark/Rimon) and can't be turned off.

Confirm it is this problem

1. Check whether your network or security software inspects HTTPS (a filter, antivirus web scanner, corporate proxy or VPN). → expect: yes; this report was in that kind of environment (our inference that the filter matters, based on the original poster's setup).
2. Check the version. → expect: 2.18.1 to 2.19.1, with an older version working on the same machine.

Not this when / boundary

The error appears on a version before 2.18.1 or on 2.21.0 and later; then check your filter or proxy settings first (our inference). For Claude Code behind a TLS-inspecting proxy, see fix/82.

Root cause

Not confirmed by Google. The original poster suspected a change in certificate handling in 2.18.1 that affects environments with HTTPS inspection; a forum replier said this error usually means a proxy, VPN or antivirus HTTPS scanner replaced or stripped intermediate certificates.

Fix

1. Update Antigravity to 2.21.0 or later. → expect: the original poster said the issue was fixed in 2.21.0, "at least on my end", without changing the filter.
2. If you can't update yet, stay on the last version before 2.18.1 that worked (the original poster's stopgap; workaround only).

How to verify

Antigravity connects to the model after signing in, with no certificate error.

What did not work

Launching Antigravity with --ignore-certificate-errors did not help (the original poster). The replier's suggestion to disable the filter could not be tested because the filter can't be turned off on that device. The replier's other suggestion (clear cached sign-in data and sign in again) was not reported as tried.

Risks

Don't turn off certificate checks or launch with --ignore-certificate-errors to get around this; it did not work here and would let anyone on the network read or change your traffic (our inference). Add an HTTPS-inspection exclusion in your security software only if your IT policy allows it (our inference).

Verified scope

Antigravity 2.18.1 to 2.19.1, October 2026.

Becomes obsolete when

Already fixed in 2.21.0; keep for users still on the affected versions.