Nixpkgs are downloaded from [[https://github.com/nixos/nixpkgs|GitHub]] and [[https://nixos.wiki/wiki/Binary_Cache|Binary Cache]]. GitHub does not support IPv6 and rate limits either [[https://docs.github.com/en/rest/using-the-rest-api/rate-limits-for-the-rest-api?apiVersion=2026-03-10#primary-rate-limit-for-unauthenticated-users|per IPv4]] or [[https://docs.github.com/en/rest/using-the-rest-api/rate-limits-for-the-rest-api?apiVersion=2026-03-10#primary-rate-limit-for-authenticated-users|per user]].
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After exhausting the API limit, Nix (or rather GitHub API) complains:
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<code>
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error: unable to download 'GITHUB_URL': HTTP error 403 ('')
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response body:
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{"message":"API rate limit exceeded for IP_ADDR. (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.)","documentation_url":"https://docs.github.com/rest/overview/resources-in-the-rest-api#rate-limiting"}
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</code>
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The solution is to [[https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens#creating-a-fine-grained-personal-access-token|create personal access token]] (Public repositories, the Permissions could be blank) and enter [[https://search.nixos.org/options?channel=26.05&query=nix.settings&type=options#show=option%253Anix.settings|the configuration]] to Nix:
