Here is a canonical Jain line that directly mentions Uttam Satya and its place among the ten dharmas:

Original text (transliteration from Digambar/Shwetambar Jain traditions):

• uttam-kham Maddavjjav sacc Sauchchaṃ ca sanjamṃ cheva
• 84. uttam-satya (supreme truth) is listed as one of the ten dharmas

What it means (arth):

• Uttam Satya means the highest truthfulness. It is part of the disciplined code of conduct (dharma) that a Jain should follow.
• The verse places Uttam Satya among ten dharmas, highlighting truthfulness as a supreme virtue, to be practiced with gentleness, restraint of speech, purity, and self-control.

Notes on interpretation:

• Digambar and Shwetambar traditions both regard satya as essential, but the exact wording or emphasis can vary slightly between the two streams. The core idea remains: speak truthfully, with restraint, and align speech with inner purity.
• Uttam Satya is not just about factual accuracy in speech; it is about speaking truth in a way that uplifts righteousness, minimizes harm, and reflects the soul’s true nature.

If you’d like, I can help look for a more precise Devanagari rendering or specific sect-by-sect variants and provide a brief comparison.