diff --git a/changelog.d/maintenance/8484-responses-transform-options-type.md b/changelog.d/maintenance/8484-responses-transform-options-type.md
new file mode 100644
index 0000000000..7c27623665
--- /dev/null
+++ b/changelog.d/maintenance/8484-responses-transform-options-type.md
@@ -0,0 +1 @@
+- Preserve the Responses API transform options contract under TypeScript 7.
diff --git a/open-sse/transformer/responsesTransformer.ts b/open-sse/transformer/responsesTransformer.ts
index 70b62a04e3..dca61a31fa 100644
--- a/open-sse/transformer/responsesTransformer.ts
+++ b/open-sse/transformer/responsesTransformer.ts
@@ -87,7 +87,7 @@ export function createResponsesLogger(model, logsDir = null) {
 export function createResponsesApiTransformStream(
   logger = null,
   keepaliveIntervalMs = 3000,
-  options = {}
+  options: { customToolNames?: Iterable<string> } = {}
 ) {
   const customToolNames = new Set(options.customToolNames || []);
   const state = {