How do you pronounce "sustainability"?

In American English: /səˌsteɪnəˈbɪlɪti/ (suh-stayn-uh-BIL-it-ee). In British English: /səstˌeɪnəbˈɪlɪti/ (suhst-ayn-uhb-IL-it-ee). In Canadian English: /səˌsteɪnəˈbɪlɪti/ (suh-stayn-uh-BIL-it-ee). In Australian English: /səstˌeɪnəbˈɪlɪti/ (suhst-ayn-uhb-IL-it-ee).

Is "sustainability" pronounced differently in American and British English?

Yes. In American English it's pronounced /səˌsteɪnəˈbɪlɪti/ (suh-stayn-uh-BIL-it-ee), while in British English it's /səstˌeɪnəbˈɪlɪti/ (suhst-ayn-uhb-IL-it-ee).