In my algo I try to backtesting some ETFs as follow:
# universe selection
context.long_portfolio = [
symbol('SPY'),
symbol('TLT'),
]
Symbol 'TLT' was not found.
Symbol X not found usually means it is not part of the dataset chosen.
We currently do not have the ETFs in our datasets. We have an workstream to include them (along with some other stuff). No concrete ETA yet for them, but expect early next year. For more information on our dataset, see here. For anything else, please drop a line here, or give us a shout at blueshift-support@quantinsti.com
Many thanks for the reply.
I am sure you know the Quantopian is closing their platform. Many people there are looking for alternative as me. This should be a good chance to win more users. Hope you cold speed up and extend your dataset work a.s.a.p. 
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Sure, we are working on some big migration project and plan to include ETFs and fundamental data right after that!