ODM has said it will make a "major declaration" on Saturday during its 10th anniversary celebration in Mombasa.
The party under Raila Odinga's Cord coalition resulted from a 2005 referendum.
It will hold a rally parallel to Jubilee Party's official launch that will take place at Safaricom Stadium Kasarani in Nairobi.
Critics have argued ODM’s event was set to divert attention from the Jubilee Party launch.
But deputy party leader Hassan Joho said: “We are 10 years old. The question of comparing us to a party yet to be born is neither here nor there."
Joho said on Tuesday that all elected ODM leaders will attend the event whose venue has not been announced. He said more details will be given on Wednesday.
“Raila will lead us... We expect to host all ODM governors, Senators and MPs."
But Johowas not certain about Kwale Governor Salim Mvurya's attendance but he said the party will grow stronger.
Mvurya and his Marsabit counterpart Ukur Yatani have defected to Jubilee and are to be officially named as members at the weekend rally.
More on this: Jubilee wins big in Coast as Mvurya ditches ODM
Mvurya’s political strategist Richard Onsango said he will give ODM’s event a wide berth and attend the JP launch.
National Assembly Majority leader Aden Duale disclosed on Monday that five governors and more than 35 Cord MPs will defect to JP during the National Delegates Conference on Saturday.
Cord members said to have jumped ship are Hussein Dado (Wiper, Tana River), Issa Timamy (UDF, Lamu) and Simon Kachapin (Kanu, West Pokot).
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