diff --git a/packages/opencode/src/session/llm/request.ts b/packages/opencode/src/session/llm/request.ts
index 0996be0f7ba4..2785d9852631 100644
--- a/packages/opencode/src/session/llm/request.ts
+++ b/packages/opencode/src/session/llm/request.ts
@@ -185,6 +185,7 @@ export const prepare = Effect.fn("LLMRequestPrep.prepare")(function* (input: Pre
           }
         : {
             "x-session-affinity": input.sessionID,
+            "X-Session-Id": input.sessionID,
             ...(input.parentSessionID ? { "x-parent-session-id": input.parentSessionID } : {}),
             "User-Agent": USER_AGENT,
           }),