In the online Oxford dictionaries at
lexico.com, the US dictionary has
nonstandard, while the UK dictionary has
non-standard. And indeed,
nonstandard is used more frequently in US publications than elsewhere. Nevertheless, even US sources use the hyphenated form more often than the single-word form. For instance, in the Corpus of Global Web-based English,
nonstandard is used 123 times in US sources, but
non-standard is used 322 times. In British sources the hyphenated form is favoured 355 to 69.
Nonstandard will lose its common word status and no longer be used as a seed word for 7-by-many puzzles.