I am very happy to announce that the Market Data Service has been deployed to production, and that the quotation endpoint in the Unified API, as of version 1.3.0, will consume market data from the new service. Aside from the vastly improved performance and cleanliness of the implementation, there are 3 key changes in how price data is formed.
Latest Price
The Latest Price endpoint will now use the midpoint of IEX TOPS bid and ask pricing during intraday requests, and will fall back to Twelve Data Real Time Price data during non-market hours. Since IEX TOPS does not have a rate limit, this is the best choice for the most frequent look-ups during regular market hours. This is also the price reference that will be used when making trades, replacing the previous Smart Quote system.
Smart Quote
The Smart Quote endpoint will now be composed of an aggregated average price across Twelve Data Real Time Price, IEX TOPS bid/ask midpoint, and Alpha Vantage Global Quote.
Cached Prices
In an effort to stay within data provider rate limits, we will now be enforcing a 2 minute cache on hits to Latest Price, Smart Quote, and Indices. Caching is done on a per symbol basis, and the data source field will reflect whether the pricing data was served from the cache layer or not. As data provider limits change, the cache TTL will be adjusted to accommodate our plan limits.
Pseudo Markets Blog 