if pure water is hydronium at 25 degrees celsius, is this true at all temps?

I'm not sure I understand what you're asking, but let me try...

Pure water is H2O. Water has the ability to "autoionize" to a very small extent. THat is, in pure water, the following reaction takes place:

H2O + H2O > H3O+ + OH-

In water at 25 degrees C, the concentration of H3O+ (hydronium ions) is very small (1X10^-7 moles/L). It is this that makes pure water at 25 have a pH of 7.0.

The concentration of hydronium ions does vary with temperature, but not too much. But, at whatever temperature there is some hydronium ion (and OH-, hydroxide ion) in pure water.