FoundationModels tool calling not working (iOS 26, beta 6)

I have a fairly basic prompt I've created that parses a list of locations out of a string. I've then created a tool, which for these locations, finds their latitude/longitude on a map and populates that in the response.

However, I cannot get the language model session to see/use my tool.

I have code like this passing the tool to my prompt:

class Parser {
    func populate(locations: String, latitude: Double, longitude: Double) async {

        let findLatLonTool = FindLatLonTool(latitude: latitude, longitude: longitude)
        let session = LanguageModelSession(tools: [findLatLonTool]) {
            """
                A prompt that populates a model with a list of locations.
            """
            """
                Use the findLatLon tool to populate the latitude and longitude for the name of each location.
            """
        }
        let stream = session.streamResponse(to: "Parse these locations: \(locations)", generating: ParsedLocations.self)
        
        let locationsModel = LocationsModels();
        
        do {
            for try await partialParsedLocations in stream {
                locationsModel.parsedLocations = partialParsedLocations.content
            }
        } catch {
            print("Error parsing")
        }
    }
}

And then the tool that looks something like this:

import Foundation
import FoundationModels
import MapKit

struct FindLatLonTool: Tool {
    typealias Output = GeneratedContent
    
    let name = "findLatLon"
    let description = "Find the latitude / longitude of a location for a place name."
    
    let latitude: Double
    let longitude: Double
    
    @Generable
    struct Arguments {
        @Guide(description: "This is the location name to look up.")
        let locationName: String
    }
    
    func call(arguments: Arguments) async throws -> GeneratedContent {
        let request = MKLocalSearch.Request()
        request.naturalLanguageQuery = arguments.locationName
        request.region = MKCoordinateRegion(
            center: CLLocationCoordinate2D(latitude: latitude, longitude: longitude),
            latitudinalMeters: 1_000_000,
            longitudinalMeters: 1_000_000
        )
        
        let search = MKLocalSearch(request: request)
        let coordinate = try await search.start().mapItems.first?.location.coordinate
        
        if let coordinate = coordinate {
            return GeneratedContent(
                LatLonModel(latitude: coordinate.latitude, longitude: coordinate.longitude)
            )
        }
        
        return GeneratedContent("Location was not found - no latitude / longitude is available.")
    }
}

But trying a bunch of different prompts has not triggered the tool - instead, what appear to be totally random locations are filled in my resulting model and at no point does a breakpoint hit my tool code.

Has anybody successfully gotten a tool to be called?