I read that Terminal 1 at HND is being extended by 6 gates, for completion in 2026. Will this be an international section for that terminal? Just like ANA has international ops at T2 (and T3). If yes, I wonder if JAL will consolidate all its ops under one roof?

All information I have read indicates the HND Terminal 1 extension will be domestic gates. Currently, all JL's domestic open gate spots (non-boarding bridge gates) which requires bus ride from the terminal are located in this new Terminal 1 extension area, which is at the north side of the current Terminal 1. I had my flights parked at this area on JL 737-800 domestic flights and J-Air E170/190 flights. What it looks like this new Terminal 1 extension will replace current open spot area used by JL, but the new Terminal 1 extension gates will be wide body capable. It looks like all JL international flights at HND will remain at Terminal3.

In 2021, the Ministry of Land, Infrastructure, Transport, and Tourism has made the statement about possibly extending HND Terminal 1 at the south end to the sideways and connect Terminal 1 (JL) and Terminal 2 (NH), where current south international area of Terminal 2 will be connected with Terminal 1 extension. This south extension area will be international capable gates. However, this seems to be an idea at this moment and no specific plan, such as initial survey, has not even started yet.

HND Terminal 1 north extension (website is in Japanese but a lot of drawings/pictures)

Thanks for the link! (Couldn't find info in English).

Tokyo International Air Terminal Corporation, the company which operates terminal buildings at Haneda, submitted 2026 budget/budget request. One of the budget requests to the Ministry of Land, Infrastructure, Transport and Tourism was a construction of artificial ground foundation over Wangan Expressway which runs through center of Haneda Airport north-south. The construction of the artificial ground foundation is at the south taxiway connecting east-west of the airport right next to the southern end of Terminal1.

Such construction is necessary if they are planning to extend southern end of Terminal 1 (JAL domestic) toward Terminal 2 (ANA international). It looks as they are serious about extending southern end of Terminal 1 toward Terminal 2 and connect Terminal 1 and Terminal 2 at the southern end. Previously Haneda Airport Authority has said that such Terminal 1 extension will be international area. Looks like that they are planning to extend southern end of Terminal 1 connecting with Terminal 2, where southern end of Terminal 1/2 will be international area for ANA and JAL.