Hey, good news, we’ve fixed the BYOK issue for gpt-5.5 on our side. Update to the latest version of Cursor, and requests should start going to your custom endpoint again, like they did with gpt-5.4.
Thanks for the detailed reports, and special thanks to @YIRU_YE for spotting the model name matching issue, it helped us pin down the root cause quickly. If anything’s still acting up after the update, post here.