I am wiring a hot tub and installed a new 50 amp circuit. I have 6 gage wire (35 feet) from the panel to the outer wall of my house. From there I am preparing to run 95 feet of THHN1 8 gage wire that I will be burying 18" under ground in grey schedule 40 pvc.

Two questions.

Is 8 gage THHN1 wire appropriate for the 50 amp circuit?

Is 95 feet too long of a run for the 8 gage THHN1 wire (as far as power loss over distance goes)?

Thank you

Just for clarification, the 6 gage wire I am running (35 feet) from my panel, is 6/3 wire.

You really have to run #6 and you have to use THWN or THHN/THWN dual rated wire. You can use a #10 insulated ground. So you need three #6 and one #10.

#8 THHN/THWN wire in conduit is perfectly fine for a 50A circuit. However, the instructions may specifically state to use #6, so check that first. Also check that they do or do not require a larger ground. Many do.
In any case the ground MUST be insulated once the circuit leaves the structure.

That's at 135 (100+35) feet @ 50A. Don't think so. #6 at 135 feet give a 2.5% drop in voltage at 240 V.

#8 at 100' 240 V gives a 3.3% (7.8 V) drop, not including the 35' (2.7%) or 1.1 Volts. Total drop 7.8+1.1 = 8.9V is 3.7% which is higher than 3%.

Motors are involved too.

A) 130' run (95+35)
B) 40 amps, not 50. The circuit is 50A, the load is likely 40 or under.
C) The run is partially #6.
D) Voltage drop is a suggestion, NOT a code requirement. Especially the 3% figure. 5% total is FINE.

Anyway,
All #8, @ 130', @ 40A, @ 240v = 3.3% drop.
This is perfectly acceptable, especially considering the section of #6 that is being used.

I am not saying #6 is wrong, it certainly is not, but it is not mandatory.