Employment contracts are virtually nonexistent here in the U.S. While the norm is “40 hours”, actual requirements vary by employer, may or may not be communicated in writing, and can change at the employer’s whim. If you make under $107,432 per year (which is around starting salary for fresh graduates at FAANG), you are entitled to overtime pay (minimum 1.5x) for hours worked beyond 40 in a week.