Direct answer
The strongest current official storefront wording supports up to four online players.
What is directly verified
The explicit four-player language is currently supported in the verified source set by:
- the PlayStation 5 storefront
- the Nintendo Switch 2 storefront
How to use this answer safely
For purchase-intent and planning purposes, the current verified answer is that Solarpunk supports online co-op with a four-player ceiling where explicitly stated by official listings.
Where platform wording is less explicit in the current source set, this page should stay careful rather than overstate parity.