Sindhi is written in Arabic script (سنڌي) and in Devanagari (सिन्धी). IndicTrans2 lists both, FLORES-200 and NLLB-200 list Arabic script only, and Meta’s MMS table has one Sindhi entry without naming a script. The 2011 Census counted 27,72,264 people with Sindhi as their mother tongue, 0.23% of India and the seventeenth largest group. Gujarat had 11,84,024, Maharashtra 7,23,748, Rajasthan 3,86,569, Madhya Pradesh 2,45,161 and Chhattisgarh 93,424. The Home Ministry says Sindhi joined the Eighth Schedule in 1967.
The Census groups Kachchhi (10,30,602 speakers) and Bhatia (22,409) under Sindhi. Sindhi proper is 16,79,246, about three in five of the group. If your clients speak Kachchhi, none of the sources tests it on its own, and it is not clear which Sindhi model would follow it.
For English meetings, the Svarah paper found Whisper large at 7.3% word error rate on speakers whose mother tongue is Sindhi, against 5.3% for native Hindi speakers.