The institute's trustees have appointed the practice to assist with assessing the existing Modernist building and winning listed-building consent for the site.
The appointment represents something of a U-turn from the trustees, who have long wanted the Grade II*-listed structure demolished, because Foster is now looking at a 'retention job'.
While nothing has yet been confirmed, Foster partner Spencer de Grey is understood to be looking to maintain the iconic building in any scheme he draws up.
In an ambiguously worded statement, the trustees refer to the next stage of the work including 'additional intensive studies into the technical capability of the building and its capacity to meet 21st century requirements for safety and the environment'.
Previously, the official line has been that the only option left for the site is demolition.
If Foster's work does rescue the 1962 building, by RMJM, it will represent another bizarre twist in the site's recent history.
Just last month the rearguard battle to save the building seemed to have suffered a fatal blow when it emerged that two government ministers were preparing legislation for parliament to delist it ( Government U-turn clears way for shock Commonweath Institute demolition).
A spokesman for Foster and Partners refused to comment except to confirm that the 'practice is in talks with the client'.