Impossible to say, with any degree of certainty, where rates will be in 3-6 years.
The ECB rate is at a historic low, with a further cut appearing likely. In the medium term, some people expect the base rate to return to a 'normal' rate of 2-3%, with deposits & mortgage rates rising in line with the ECB rate. Then again, rates could remain, at low levels, for a sustained period.
One strategy might be to hedge your bets by splitting your deposit into different terms.