Friend shocks me by suddenly saying he's female. How to handle this?

What utter drivel.

I had the same, was the sweetest gentlemanly trans I every had around me....adorable tall masculin man

If this project is designed to make money for both of you through a company you own, I wouldn't assume that this man won't have a discrimination claim against you if you drop him from the project for trans-related reasons. I'd get legal advice before doing or saying anything to him that he won't like.
You say that his pronouns are currently he/she, so there seems to be some flexibility at the moment, but of course that may well change.

I’d just take a ‘that’s nice, dear’, approach. He’s allowed to have his beliefs. You don’t have to agree with him. I’d just not discuss it unless it actually becomes a problem.

I can honestly say that I met worse people who are clearly male or female than the trans people I have met.
I am not trans myself. I just worked with them.
Depressing thread.

I'd cancel the project. I've no time for this BS.

They MUST be someone else with similar expertise. This MAN cannot be the only person who knows the info you require. After all, HE learned it from someone at some stage.

Ok, so they are a friend....very much manly looking but now self declared a woman's identity....since they know each other, he or she might wants sex....so?

I agree with this approach.

You wanted to engage your friend on a project that you hope will make you both money but not involve any contract, formal agreement or paperwork ? That will entail you working closely together for months ?
I get it relates to your hobby but it sounds like a serious task. Not to have anything in place sounds risky to me. Irrespective of anything to do with his transition. How much money would be being put into this project ? That alone would require some sort of agreement.
And if you have one of those you do need to consider legalities.

They are the same person they were before, if you got on well before theres no reason why that should change.

Trans people understand it takes a while for others to get used to new names and pronouns, I'm sure it won't be an issue if you accidently use the wrong one.

However. What is an issue is your bigoted attitude, maybe it will be better if you dont work with her, but make sure you tell people the reason why.....that instead of supporting a colleague and friend, you'd rather give up the project. You shouldn't ask to remove them or cancel the project, you need to remove yourself from it and give him the chance to work with someone supportive.

Have just seen this, so in this situation I find it somehow worse that he hasn't made contact.

I worked with someone in 1999 same thing , very masculine looking, builders build , big hairy legs, used to come to work in a mini dress and stilettos, no tights. It’s challenging to say the least.

I’d keep going. Use the name that’s suggested; everyone has the right to change their name. Start stripping your language of pronouns - it gets easier - and use she if you have to.

Just be as normal as you can. Ignore the transition - it’s their business. Practice a couple of neutral responses like ‘I’m not very interested in clothes’ if they try to involve you in discussions of their outfit (this has happened to a friend. Of course that won’t work if you are madly into fashion).

I'd definitely not have a conversation about it that could be turned against you - and don't imagine that couldn't happen. I'd just let the project drift and think about a way you might do it without him in the future.

Even if I can manage to avoid the pronoun thing, how can I stay silent or dodge the subject if he looks me right in the eye and tells me he's now female?

“I’m not obliged to play along with your fantasies but by all means you do you” would suffice.

I am Slavic and I cannot believe how much people beat around the bush on this topic in the UK. You do realise they’re not qualified to argue with science no? I’ve no time for such nonsense.

What the fuck?

I am christian and worked with trans people. I called them by name

I am really sorry you are being put in this position.

And would like to add that as this is your project and you invited him to be part of it, would like to think rather than expecting you to just accept some general announcement on SM or where ever he would get in touch with you!

But as now seems to be the norm everyone else is supposed to adjust to their "reality".

Also, a PP referred to work colleagues being expected to be kind and used the preferred pronouns of the trans person.

However the Forestater case made clear that both "beliefs" have equal status ie sex realist vs. sex identifiers.

But think the suggestion made by others to say to him, its your life but as I know you as Joe Blogs and invited you to work with me as Joe Blogs that is who you will be to me as a co-worker. (Thanks for your understanding Joe!)

Best of luck

The level of autonomy you have doesn't make it sound like a project set by an employer.

I am very gender critical but I think you need to be careful you don't get dragged into a discrimination case if it's a service or organisation you're involved with, even if voluntary.

I'd probably let the project die a death - make excuses that can't be challenged if necessary, like 'personal reasons' .

Ultimately you need to decide if the mental/ethical gymnastics are worth your time and energy vs how much the project matters to you.