Vercel · sdk · fg-0246

useChat sends a stale value in DefaultChatTransport body after React state changes

Server always receives the first render value from transport body

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

Cause

useChat creates its Chat instance once and kept the transport from the first render, so values captured in transport body never updated. The fix landed in July 2026 (PR 16546).

Fix

Upgrade @ai-sdk/react to 3.0.223 or later on the ai 6 line, or 4.0.12 or later on the ai 7 line. On ai 5, which has no fix, pass per request data in the sendMessage options instead of the transport.

Apply

sendMessage({ text: input }, { body: { subagent } });

Affects: @ai-sdk/react before 3.0.223 (ai 6 line) and before 4.0.12 (ai 7 line); the ai 5 line has no fix

Sources

Have your agent know this before it fails

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