diff --git a/cmd/olliesrv/internal/agent/turn.go b/cmd/olliesrv/internal/agent/turn.go
index ae8b160..bcdbadb 100644
--- a/cmd/olliesrv/internal/agent/turn.go
+++ b/cmd/olliesrv/internal/agent/turn.go
@@ -320,9 +320,19 @@ func (ag *Agent) executeTurn(ctx context.Context, input string) string {
 	return ""
 }
 
-// autoCompactLimit returns the token threshold for auto-compaction (75%).
+// autoCompactLimit returns the token threshold for auto-compaction (75% of
+// the compaction model's context window). Compaction may use a different model
+// from the active turn model, so querying the active model here can overestimate
+// the request limit.
 func (ag *Agent) autoCompactLimit(ctx context.Context) int {
-	ctxLen := ag.runtime.Backend.ContextLength(ctx)
+	b := ag.runtime.Backend
+	compactModel := resolveCompactionModel(ag.runtime.CompactionModel, b)
+	origModel := b.Model()
+	if compactModel != "" && compactModel != origModel {
+		b.SetModel(compactModel)
+		defer b.SetModel(origModel)
+	}
+	ctxLen := b.ContextLength(ctx)
 	if ctxLen <= 0 {
 		ctxLen = defaultContextLength
 	}