Are Shimano and SRAM 11-speed compatible?
Partly. At 11-speed road, the Shimano/SRAM chain and cassette interchange without problems. BUT the shifter and derailleur must be the SAME brand: Shimano and SRAM use different cable-pull ratios, so a Shimano shifter won't drive a SRAM derailleur correctly (and vice versa).
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Source: Park Tool / BikeGremlin. Indicative data — always check the manufacturer's official specs.