Main points in favor of this grant
I believe policy to be a high-leverage field, as demonstrated by the success of Open Philanthropy's support for American biosecurity policy efforts--in particular, it's a high-leverage field where success is often somewhat difficult for outside observers to see. I think Australian policy is probably undervalued, due to the majority of donors being clustered in the UK and US. Australia is a relatively small country, so I'd guess there is potential for Australian policy to be positively influenced through the efforts of fewer people than it takes in the UK and US. Although there are many countries that are more immediately influential on an international stage, Australia is a relatively wealthy country with strong cultural similarities and political ties to the UK and US, and is an economic leader in the Pacific region, so it could be a good place to test policies that then influence other countries--Chelsea Liang from GAP informed me that plain tobacco packaging began in Australia and has since been adopted by over 20 other countries.
I also second everything Joel said, particularly the points about a) Greg Sadler's deep understanding of Australian policymaking and b) the terrible incentives demonstrated if GAP's work goes unfunded. It matters a lot to me that Greg clearly seems to think that he'll be more impactful outside of the civil service than within it--this seems like a clear-cut case of being able to take cues from people on the ground, and to counteract regional over-centralization within charitable networks.
Donor's main reservations
Pretty simple: when deciding on how to use my regranting budget, I had a preference for opportunities where my marginal grant was more likely to make a difference as to whether a project moved forward (or moved faster). It currently seems reasonably likely for GAP to shut down anyway, in which case my grant wouldn't really have done much! But I really hope the grant does matter, and I think GAP deserves the vote of confidence either way, in case it helps sway other grantmakers in the future.
I slightly share Joel's reservation about Australian policy not seeming especially important in reducing catastrophic risk, but it's not as strong of a reservation: as I wrote above, I think policy levers seem effective to a degree that might surprise outside observers, and policy requires serious on-the-ground experience, so I would expect policymaking to be undervalued in countries without major grantmaker concentrations.
However, I have a related reservation about how this grant falls under the philosophy of hits-based giving: I myself work on pretty speculative projects, for an organization that runs pretty speculative policy projects, and I previously gave a grant to a pretty speculative policy project. When working on catastrophic risk, most projects might be speculative, but Australian policy advocacy is perhaps more so than, e.g., direct research or similar. I considered that I might be "investing" too much of my "impact budget" highly speculative projects, when possibly the money would be better spent by another grantmaker pursuing less hits-based/speculative grants.
Process for deciding amount
$5k is what I had left in my regrantor budget!
Conflicts of interest
Minor: Chelsea Liang, who worked at GAP, is a colleague and friend; she previously worked with me on a strep vaccine project. I value her opinion, so I asked her for further information about GAP's work and the potential for Australian policy to impact catastrophic risk before deciding on this grant. She is not a recipient of the grant. Greg, who is a recipient, provided some advice on the strep project at one point.