There was considerable disagreement among the Allies (surprise) on how to treat Austria - as an enemy state, or as the first victims of Hitler's aggression. It was the only state entirely annexed by the Third Reich, which also complicated things. Like Germany, Austria was divided into four zones, and like Berlin, Vienna was too - except for the city centre within the Ringstrasse which was an "International Zone" patrolled jointly by all four powers together - the so-called "Four in a Jeep" period. The movie The Third Man (a cracking watch if you haven't seen it) is set in this period.

Between the Korean war and the various other Cold War crises, there were more pressing issues than sorting out something permanent for Austria, but when Stalin died and Malenkov took over, things moved and all four powers agreed to withdraw from Austria as long as she remained neutral and with severe limitations on her military capabilities. This was finalised in 1955.

This article over at the Department of State archive site gives a good overview of the American side of negotiations.

This suggests that the Soviets were willing to give up territory - the only time they did so - basically because they'd already expropriated all they could manage and the small bit of Austria they had was worth more as a political bargaining chip - by showing willingness to negotiate, the Soviets forced Eisenhower in turn to soften and meet him. Moreover, Austria as a neutral state split the northern (German) and southern (Italian) flanks of NATO, so there was geopolitics behind it as well.