SIX and Clearstream aim to have a memorandum of understanding in place by mid-December.
Partnership set to provide proof of concept for blockchain tech in Swiss financial markets.
Renewal of agreement comes after competitive tender process.
SIX recorded strong results in its securities services business in the first half of the year.
SIX Group CFO Stefan Mäder will leave the position at his own request after six years in the role.
MTF will go interoperable with extended clearing options which LCH and X-clear say will improve netting opportunities.
Citi has been awarded a mandate from SIX Securities Services to provide custody services for $230 billion of assets.