public String compileVersion(ApplicationId id, OptionalInt allowMajor) {
        URI url = compileVersionPath(id.tenant(), id.application());
        if (allowMajor.isPresent()) {
            url = withQuery(url, "allowMajor", Integer.toString(allowMajor.getAsInt()));
        }
        return toInspector(send(request(HttpRequest.newBuilder(url).timeout(Duration.ofSeconds(20)),
                                        GET)))
                .field("compileVersion").asString();
    }
Returns the Vespa version to compile against, for a hosted Vespa application
hosted-api/src/main/java/ai/vespa/hosted/api/ControllerHttpClient.java