Anthropic's systems experienced elevated errors on seven of the past 22 days, including four consecutive days from April 6 through 9 — the most sustained reliability strain the company has faced since a March 17 outage knocked out Claude.ai for hours. The April 7 incident was the most visible of the recent stretch: Claude Code authentication failed for 40 minutes when the domain auth.anthropic.com stopped resolving, a DNS failure that locked out any developer whose session needed re-authentication during that window.
The root cause was documented in GitHub issue number 33238, opened by a developer and subsequently acknowledged by Anthropic. Running nslookup on auth.anthropic.com returned "Non-existent domain." OAuth tokens tied to the subdomain timed out with no client-side resolution path available. The distinction matters: users who were already authenticated with a valid session could continue using Claude Code during the outage. Users who needed to refresh or establish a new OAuth handshake could not. For developers whose workflow requires periodic re-authentication — a standard security practice — the failure was total.
The April 6-8 sequence was more sustained than a single incident. On April 6, from 15:00 to 16:30 UTC, elevated errors hit login for both Claude.ai and Claude Code, according to the Anthropic status page. On April 7, from 14:32 to 15:12 UTC, a second wave struck across authentication systems. Business Insider, citing Down Detector, reported thousands of user complaints by mid-morning on April 7. That same day at 23:00 PT, Sonnet 4.6 — Anthropic's flagship reasoning model — began exhibiting errors above baseline, a separate wave that persisted until 01:50 PT on April 8, per the status page. A third incident began April 8 at 06:23 UTC; Anthropic identified the issue at 07:59 UTC and deployed a fix by 09:33 UTC, the status page shows.
The pattern matters because of who it affects. Claude Code is a paid product. Developers who rely on it as a daily driver have a different relationship with the tool than free-tier users encountering slow responses. Gauresh Pandit, a senior software engineer at Meta, told Business Insider in March that AI coding tools have become a single-button action for getting software engineering tasks done. If authentication fails, that button does not work — regardless of how reliable the model underneath is.
Three of the seven incident days since March 17 involved authentication or login systems. The infrastructure supporting Claude Code and its OAuth handshake has now been implicated in at least two of those incidents. This matters for a product that Anthropic has positioned as stable and production-ready. For an AI company, reliability is not a feature alongside the model — it is the product.
Anthropic has not published a post-mortem for any of these incidents. Its status page entries document when errors began and when they resolved, but they do not explain what went wrong or what steps are being taken to prevent recurrence. That is an unusual posture for a company that has made trustworthiness and interpretability central to its brand.
Anthropic declined to comment beyond its status page updates.
The company that built Claude on reliability and trustworthiness is running a reliability problem it has not explained.