It sounds like they may be reviving a cash balance pension plan.
In 1999, IBM moved anyone under 40 and/or with less than 15 years' service from the "old" defined benefit pension plan to a cash balance plan. They were later successfully sued and starting in 2004, new hires were only eligible for an enhanced 401k. Those who had funds in the cash balance plan retained them, but in 2006 IBM froze the plan and ceased any additional contributions.
Cooper v. IBM Personal Pension Plan
There was also a tweak to the "old" pension plan in 1995.
For the 1999 version, per the linked article here is how the interest rate was set for that cash balance plan:
"Effective July 1, 1999, IBM again amended its Plan to create its Cash Balance *1013 Formula ("CBF"). Under the CBF, a participant's benefit is determined by reference to a hypothetical account known as a Personal Pension Account ("PPA"). Every month, a participant's PPA accumulates "pay credits" at a rate of 5% of the employee's salary and "interest credits" at a rate one percentage point higher than the rate of return on one year treasury securities.
For the 1999 version, when you left IBM (retiree, resource action, or voluntary separation) you were able to rollover the cash balance PPA into an IRA. Back in '99, there was quite the uproar, with some calculations circulating amongst employees that the change from defined benefit to cash balance would essentially slash the net pension benefit value by nearly 75%.
As you can see from this history, a company's retirement offerings can change throughout one's employment.