px size for submitting [Generative AI artwork]?

More than 4 mega pixels, but do not upsize. Upsizing does not create better pictures, but amplifies the artefacts in the picture. Indeed, all quality requirements are the same for AI or non-AI assets. AI assets just need specific additional indications during the submission phase.

If you are new to stock, you should consider these resources: https://helpx.adobe.com/stock/contributor/tutorials.html
Please read the contributor user manual for more information on Adobe stock contributions: https://helpx.adobe.com/stock/contributor/user-guide.html
See here for rejection reasons: https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
and especially quality and technical issues: https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html

If you are a generative AI contributor, please look into these instructions and follow them by the letter: https://community.adobe.com/t5/stock-contributors-discussions/generative-ai-submission-guidelines/td-p/13549435

Tip: be sure you are not, at any point, INCREASING the size in pixels. It's forbidden. You must make it at the size you submit (or reduce to that size).

Since AI is considered an illustration I assume the same technical parameters are applicable as for all other illustrations:

https://helpx.adobe.com/stock/contributor/help/photography-illustrations.html