STR Loophole – Buying Property with LTR tenant till Sept, convert to STR?

I'm evaluating a tax strategy on a duplex purchase and would like a second opinion on a specific technical question before I commit. Brief context:

– I'm purchasing a duplex in CA, closing approximately May 2026. One parcel number. Two addresses (Unit A, and Unit B )

– I plan to live in Unit 2 as my primary residence

– Unit 1 has an existing long-term tenant whose lease terminates Sept 30, 2026

– Starting Oct 1, 2026, I plan to convert Unit 1 to a short-term rental on Airbnb for the remainder of the year, targeting an average guest stay of under 7 nights

– My goal is to qualify Unit 1 as a non-passive STR activity under Treas. Reg. §1.469-1T(e)(3)(ii)(A) and use cost segregation + bonus depreciation to offset W-2 income via material participation

My specific question:

For purposes of the 7-day average period of customer use test, can the LTR period (May–Sept) and the STR period (Oct–December) be treated as **two separate rental activities** under §469, rather than aggregated into a single activity?

If they are separate activities, the LTR period stands alone as passive and the STR period averages under 7 nights — clearly qualifying. If they must be aggregated, the LTR stay (1 customer) gets blended into the calculation and pulls the annual average up substantially. I wouldn't be able to get the average stay under 7 days.

I've seen this analyzed under the §469 grouping regulations and the Treas. Reg. §1.469-4 facts-and-circumstances test for what constitutes an "appropriate economic unit."

Curious…from an expert or two…would you (and the IRS) treat these as separate activities for §469 purposes?