I have been looking for a roundtrip BOS-CGB through GRU in J for September 2025. When the tickets just became available, the cost was ~$3,800. Then they changed the schedule and the price climbed to $4100. In January, it was ~$4,300 for flights with either direct BOS-GRU segments or BOS-ATL-GRU; the JFK-based segments (BOS-JFK-GRU) climbed to $5,200. Finally, this week only 1 flight (out of >20) remained at $4,300, all the others climbed to $4,800 (direct or through ATL ) and reached >$5,600 for flights through JFK.
So it looks like a systematic price increase as the seats availability did not change