I decided to switch to an Anthropic developer account and use BYOK in Cursor in order to reduce token costs, because at this point the markup on usage is becoming excessive. What was frustrating is that nowhere in the setup flow, documentation, or settings was it made clear that the models might behave differently under BYOK than they do when routed through Cursor’s own paid usage.
The moment I enabled BYOK, Claude Opus 4.6 started behaving noticeably differently. It began bypassing direct instructions to invoke skills, skipping entire sections of established workflows, shortening or simplifying requests in ways I did not ask for, and making silent edits that were not aligned with the instructions given. Instead of operating like a dependable agent, it started feeling inconsistent and difficult to control.
After roughly eight hours of fighting with the model and dealing with the kind of degraded behavior that reminded me of the problems I had in Windsurf, I decided to disable my API key and switch back to Cursor provided usage just to test whether BYOK was actually the source of the issue. The difference was immediate. Everything went back to normal. Skills were being invoked correctly, instructions were being followed properly, and the overall usability of the agent returned almost instantly.
That is what makes this so disappointing.
If Cursor is going to promote BYOK as an option for developers, then there should be clear disclosure if the experience is not functionally equivalent. Offering users the ability to bring their own key while silently degrading the actual usefulness of the agent feels misleading. It creates the impression that cost savings are being offered with one hand while core reliability is being taken away with the other.
At a broader level,
this feels like a slap in the face to the people actually trying to use these tools seriously. It raises an obvious question: are software companies becoming so focused on protecting margins that they are willing to compromise the user experience they advertise? More and more, it feels like profit is being prioritized over transparency, reliability, and trust.