The reason, he said, at the annual Red Hat Summit in Boston this week, is that the deal is still subject to regulatory approval.
As it happened, the United States Department of Justice gave its approval of the $34 billion deal on Monday. The deal, the biggest in IBM's history and the world's biggest software acquisition to date, is still dependent on the approval of a number of other regulatory bodies, including those in China and Europe.
If this approval is granted, the open source company will form part of IBM's hybrid cloud unit, but has asserted it will retain its independence.
Whitehurst believes the companies share the same vision of hybrid, multi-cloud.
"I'm really excited with IBM's breadth and scale. With our infrastructure stack and what we're doing in open source communities, we can provide tremendous value to enterprise customers. They're looking to move from traditional infrastructure to hybrid and multi-cloud.
"I would rather be owned by IBM, which is passionate about open source, than a bunch of mutual funds which couldn't care less. I think we have a better capability as part of IBM to deliver our aspirations for open source than we could as a private company."
It can be seen as a triumph for the 26-year-old company to be bought by IBM, which was founded in 1911, as well as positive a move for open source software, which is now integral to almost every business.
The rise of open source has placed the developer at the centre, or near the centre, of the business, and it is they who conceptualise, tweak and finally bring the software to life. In the case of Red Hat, and other open source companies, this software is then hardened and secured for use in the enterprise.
In delivering his keynote at the summit, Whitehurst was joined on stage by, separately, the two CEOs of the world's largest IT companies: IBM CEO Ginni Rometty and Microsoft CEO Satya Nadella, who announced support for Red Hat's OpenShift on Azure.
Rometty said she believes many companies are already on their cloud journey, and looking for ways to modernise their applications and connect their disparate workloads.
"Linux, Kubernetes and containers are going to form what I think is a (new) standard for the world."
Whitehurst believes that in the next five years, a new architecture of technology is going to emerge and will involve public clouds and containers.
Meanwhile, the public clouds are attempting to differentiate themselves and are "drifting further apart".
"We think about cloud as a deployment model, and a container platform being the equivalent of an OS," he said, adding it is vital to have a consistent infrastructure stack which runs across all clouds.
Red Hat's offering in this regard is the containerisation software OpenShift, which Whitehurst said is the only infrastructure stack which runs exactly the same on bare metal, or VMware, Amazon, Google or Alibaba clouds, for example. OpenShift provides developers with an environment in which containers can be built and deployed, which are then controlled using the Kubernetes orchestration platform.
"In fact, I think it's why IBM was so interested in Red Hat; it's ensuring that vision of hybrid multi-cloud, which is a consistent infrastructure stack."
Whitehurst said as long it continued to deliver value to its shareholders, they would continue to give Red Hat latitude to continue working with open source communities.
He also believes his company has a sustainable source of competitive advantage, because of its ability to work with upstream communities. Others, such as Oracle, had a database product, and then "they basically bought everything else that's in their portfolio. CA had their original management tool and they bought a lot of stuff."