Safari on iOS 26 (Developer Beta 6 & Public Beta) – Direct Line WebSocket connection fails with “There was a bad response from the server”

We are experiencing an issue with Bot Framework Direct Line when running in Safari on iOS 26 (both Developer Beta 6 and Public Beta).

When trying to connect to Direct Line using WebSockets, the connection fails immediately with the following error:

Websocket connection to 'wss://directline.botframework.com/v3/directline/conversations....' failed: There was a bad response from the server. 

Environment details:

• Frontend: botframework-directlinejs (tested with 0.10.0 and 0.15.6)

Backend: Microsoft.Bot.Builder 4.17.1

Endpoint: wss://directline.botframework.com/v3/directline/conversations

Works fine on: Chrome (iOS 26), all desktop browsers, previous iOS versions.

Fails on: Safari (iOS 26 Developer Beta 6 & Public Beta) – both on device and via WKWebView.

Notes:

• Network inspector shows that the WebSocket request is sent, but Safari aborts immediately after handshake with “bad response from the server.”

No public reports of this issue found yet.

Steps to reproduce:

Open any Direct Line Web Chat instance in Safari on iOS 26 Beta.

Inspect console/network.

See that WebSocket fails to connect with “bad response from the server.”

Expected behavior: WebSocket should connect successfully, as in previous iOS versions and other browsers.We are experiencing an issue with Bot Framework Direct Line when running in Safari on iOS 26 (both Developer Beta 6 and Public Beta).

When trying to connect to Direct Line using WebSockets, the connection fails immediately with the following error:

Websocket connection to 'wss://directline.botframework.com/v3/directline/conversations....' failed: There was a bad response from the server. 

Environment details:

Frontend: botframework-directlinejs (tested with 0.10.0 and 0.15.6)

Backend: Microsoft.Bot.Builder 4.17.1

Endpoint: wss://directline.botframework.com/v3/directline/conversations

Works fine on: Chrome (iOS 26), all desktop browsers, previous iOS versions.

Fails on: Safari (iOS 26 Developer Beta 6 & Public Beta) – both on device and via WKWebView.

Notes:

The same bot works correctly when webSocket is disabled (HTTP polling).

The issue is reproducible even with the sample Direct Line Web Chat client.

Network inspector shows that the WebSocket request is sent, but Safari aborts immediately after handshake with “bad response from the server.”

This might be related to stricter WebSocket handshake validation in iOS 26 Safari.

No public reports of this issue found yet.

Steps to reproduce:

1. Open any Direct Line Web Chat instance in Safari on iOS 26 Beta.

Inspect console/network.

See that WebSocket fails to connect with “bad response from the server.”

Expected behavior:
WebSocket should connect successfully, as in previous iOS versions and other browsers.