GitHub App installation tokens are now 520 characters: What to check before November 30

GitHub App installation access tokens have transitioned from 40-character opaque strings to variable-length, roughly 520-character stateless tokens in a `ghs_APPID_JWT` format, while retaining the same prefix, permissions, repository scope, endpoint, and one-hour expiration. The change affects GitHub Enterprise Cloud and Data Residency installation tokens, including Actions `GITHUB_TOKEN`, but not GitHub Enterprise Server or currently `ghu_` user tokens. Organizations should treat tokens as opaque values and audit validation patterns, secret-redaction rules, database and secret-store field sizes, environment variables, and proxy or gateway header limits, since assumptions about fixed length or alphanumeric-only content can cause rejections, truncation, authentication failures, or unredacted credentials in logs. GitHub recommends supporting token patterns that allow dots, hyphens, underscores, and open-ended length, while testing with genuine stateless tokens rather than legacy fixtures. Until November 30, 2026, applications can request either format through the `X-GitHub-Stateless-S2S-Token` header, but GitHub will then ignore the header and always issue stateless tokens, making it important to remove temporary opt-out settings and complete compatibility checks before that deadline.

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