Microsoft and Yahoo openly acknowledged last week that their search partnership would result in some Yahoo employees shifting to Microsoft, as the Redmond company's plan takes over search development for both. Turns out they aren't leaving it to chance.

Yahoo today filed new details about the agreement with the Securities and Exchange Commission -- including the fact that the partnership requires Microsoft to hire "not less than 400" employees from Yahoo. The provision would kick in after the companies finalize the deal, which still hinges on regulatory approval in the U.S. and overseas. Here's what the filing says about the transition.

As promptly as practicable, Yahoo! and Microsoft will agree on a detailed transition and implementation plan and schedule for implementing Microsoft’s algorithmic search services and paid search services on all Yahoo! Properties and Syndication Properties. The transition and implementation plan will be for a period of no longer than 24 months from the Commencement Date, subject to an extension for up to three additional months if the end of the 24-month period ends during the fourth quarter of a calendar year. The parties intend that the transition and implementation plan will be either set forth in a separate transition services agreement or as part of the Search Agreement.

Following the Commencement Date, Microsoft will hire not less than 400 Yahoo! employees (the “Transferred Employees”) and will offer the Transferred Employees market competitive compensation packages. In addition, Yahoo! and Microsoft will mutually agree on a retention plan to be paid for by Microsoft to assist in retaining the Transferred Employees and an additional 150 Yahoo! employees to be mutually agreed upon between Microsoft and Yahoo! to assist with providing the transition services.

Microsoft has hired several former Yahoo executives in recent months, including Qi Lu, now the president of Microsoft's Online Services Business. The Redmond company has significant operations in Silicon Valley, so it's possible that many of the workers could remain in California even after shifting between the companies.

[Follow-up: Yahoo can escape Microsoft deal if it doesn't measure up to Google.]

[Via The Associated Press]