Who actually has to carry it, regardless of the general rule
The state-level opt-out applies to most private employers, but it isn't universal: government entities and public employers generally must carry coverage, and many government contracts and some construction agreements require proof of workers' comp as a condition of the work — regardless of what Texas law otherwise permits. It's worth checking the actual contract or bid requirements rather than assuming the opt-out settles the question for a given job.
What “nonsubscriber” status really means
Opting out doesn't mean the business is protected from injury claims — it means the business loses the traditional workers' comp trade-off. A nonsubscribing employer can be sued directly by an injured employee, without some of the legal defenses (like the exclusive-remedy protection) that subscribing employers have, and without the caps a comp system otherwise puts on covered costs. In practice, that can mean broader financial exposure, not less.
What most small businesses end up doing
Plenty of small Texas employers carry standard workers' comp anyway once they have employees and real payroll, simply because the coverage and legal protection outweigh the savings from opting out. Businesses that do stay nonsubscribers often pair that decision with occupational accident coverage to cover at least some of the same ground. Either way, a certificate of insurance showing workers' comp is frequently required just to bid or perform certain jobs — separate from whether Texas technically mandates it.