He said his campaign is "negotiating almost every day with the Clinton people" to push her to take more progressive positions.
Sanders said: "Our job now is to have her listen to what millions of people in this country who supported me want to see happen."
He did not say whether he would endorse Clinton with whom he has fought an at times bitter battle.
Sanders has still not suspended his campaign and it remained unclear whether he would drop out of the race before the convention, where he still hopes to speak.
The democratic socialist senator said: "I've given a few speeches in my life. It would be nice to speak at the convention.
"If for whatever reason they don't want me to speak then whatever. But I do think I'll speak at the convention."
Sanders also said he would do everything possible to prevent Donald Trump, the presumptive Republican nominee, from becoming president.
He said: "The major political task we face in the next five months is to make certain that Donald Trump is defeated."
