A solid top is a little wider in August than in February. On a 90 cm table that is about two millimetres, and you will only notice it as a fractional overhang at the breadboard end.
That movement is designed for. The tops are not glued across their width, the panels sit loose in their grooves, and the ends are pegged rather than fixed. Stop the wood moving and it splits instead.
What you can do: keep it out of the path of a radiator or a wood burner, and do not stand it in front of a south-facing window for a year and expect the colour to be even. Both are heat, and heat is what solid timber minds.