Based on arguments for harm reduction and health benefits, tobacco companies in the United States can apply for regulatory authorization to make "modified risk tobacco product" (MRTP) marketing claims. The impact of future MRTP claims may depend on whether they are noticed, believed, and lead to smokers switching products. This study provides baseline data about smokers' exposure to perceived MRTP claims ahead of any MRTP authorizations. We analyzed measures from Wave 3 of the US-based Population Assessment of Tobacco and Health (PATH) study which asked smokers to indicate if they had seen any e-cigarettes, snus, or other smokeless tobacco (SLT) products that claim to be "less harmful" in the past 12 months, and their likelihood of using products with these claims in the next 30 days. Significantly fewer smokers noted having seen snus (5.1%) or other SLT (5.6%) with "less harmful" claims compared with e-cigarettes (29.1%). For each product, the prevalence of MRTP claim exposure was higher among smokers who perceived the product to be less harmful than smoking, who currently used the product, and who had higher rates of tobacco advertising exposure at the point of sale. Among smokers who noticed products with "less harmful" claims, about one-quarter said they would use them in the future (24%-27%). Ahead of any Food & Drug Administration (FDA) authorization for MRTP claims, some smokers already perceive exposure to "less harmful" claims for e-cigarettes, but few do for SLT. MRTP claims may motivate some smokers to use these products. This study provides new baseline data about smokers' perceived exposure to MRTP claims in the United States ahead of any regulatory claim authorization. Using data from Wave 3 of the US PATH study, we found that some smokers already perceive exposure to "less harmful" claims for e-cigarettes (29%), but few do for SLT (5%-6%). Among smokers who noticed products with "less harmful" claims, about one-quarter said they would use them in the future (24%-27%), suggesting MRTP claims may motivate some smokers to use products described as "less harmful."