Vercel · infra · fg-0242

Pages cached on Vercel started returning x-vercel-cache MISS on every request after September 30, 2026

x-vercel-cache: MISS on routes that used to HIT

Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100

Cause

Since September 30, 2026 the Vercel CDN refuses to store any response whose Vary header names Cookie. Middleware or frameworks that add Vary: Cookie globally make those routes uncacheable.

Fix

Remove Cookie from Vary on routes that do not change per visitor, and set Vary only on the routes that need it.

Apply

// before: Vary: Cookie, Accept-Encoding
// after (cacheable):
headers: { 'Cache-Control': 'public, s-maxage=600', Vary: 'Accept-Language' }

Affects: Vercel CDN, since 2026-09-30

Sources

Have your agent know this before it fails

claude mcp add --transport http footgun https://getfootgun.com/api/mcp