What you can do

One SDK works against every STX exchange. Not every exchange has every feature yet. A call that needs a feature the exchange does not have throws STXNotAvailableException, and GetCapabilitiesAsync() tells you up front, so the same code runs against Ontario production today and picks up new features as each exchange gets them.

Features and their calls

Feature	Id	SDK calls	Guide
Markets, events and prices		GetMarketsAsync, GetAllMarketsAsync, GetMarketAsync, GetEventsAsync, GetAllEventsAsync; channels OrderbookAsync, TickerAsync, TradesAsync, MarketAsync, MarketsAsync, MarketStatsAsync, MarketUpdatesAsync	Markets, WebSockets
Trading		PlaceOrderAsync, PlaceOrdersAsync, CancelOrderAsync, CancelOrdersAsync, CancelAllOrdersAsync, GetOrdersAsync, GetOrderAsync; cancel-on-disconnect on OrdersAsync	Trading
Your account		GetMeAsync, GetBalanceAsync, GetPositionsAsync, GetFillsAsync, GetSettlementsAsync, GetAccountMarketStatsAsync, GetDepositsAsync, GetWithdrawalsAsync, GetAdjustmentsAsync, GetFeesAsync, GetLoyaltyAsync, AcceptTermsAsync; AccountViewAsync and the account channels	Portfolio, WebSockets
Combos	combos	RfqAsync, ComboQuoteAsync	Combos
Leaderboard	leaderboard	GetLeaderboardAsync, GetLeaderboardStandingAsync, UpdateProfileAsync
Market types	market_types	GetMarketTypesAsync
Event players	event_players	GetEventPlayersAsync
Create markets	markets.create	CreateMarketsAsync	Create markets

GetCapabilitiesAsync() also reports oauth, oauth.member, oauth.app, connect, terms.stx_page and markets.create, from the exchange’s published OAuth metadata.

Ask the exchange

using var client = new STXClient();
var caps = await client.GetCapabilitiesAsync();
foreach (var f in caps.Features.Values)
    Console.WriteLine($"{f.Id}: {f.Available?.ToString() ?? "unknown"} ({f.How})");
// leaderboard: False (GET /api/v1/leaderboard?limit=1 answers 404 'Leaderboard is not enabled')
// combos: True (rfq join answered 'unauthorized' (the channel exists))

Every probe is a read: discovery documents, GET routes, and one channel join that is left at once. Nothing is created, changed or placed. The answer is cached on the client; refresh: true asks again, and probeChannels: false skips the socket (combos is then unknown).

caps.Available("combos") is true only when the exchange showed it has the feature; a feature that could not be decided is null and counts as not available. caps.Require("combos") throws STXNotAvailableException when the feature is known to be absent.

When a feature is not available

try
{
    var types = await client.GetMarketTypesAsync();
}
catch (STXNotAvailableException ex)
{
    Console.WriteLine($"{ex.Feature}: {ex.Message}");
    // market_types: Market types are not available on demo.stxapp.ca yet.
}

Nothing else on the client is affected: only the call that needs the feature throws. A channel the exchange does not have throws STXChannelUnavailableException, whose Feature is channel.<name>.