Go is played with various rules and there are also variatoins of the game. Which do you think deserve to be called go? Which ones do need a prefix for word go?

Go with Japanese rules, 6.5 komi
Go with Chinese rules, 7.5 komi
Go with Ing rules, 7.5 (or 8) komi
Go with some other rules
Go with no komi
Go with Hahn system
Bangneki
Pair Go
13*13 go
9*9 go
Other, insert you variant

They are all go, of course, as the word "go" is in the description.

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Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).

These I do not consider go, but games / go variants closely related to go because strategy and risk-strategy differ greatly.

Go with non integer komi allows two results: black wins or white wins. Go with no komi or with integer komi allows a third results: jigo. Hahn system allows ten different results. On how many different results would you draw the line between go and go like game?

Also from the view point of a single player pair go seems to differ from go.

I'd stick with at most 3 possible results as "go," to keep with tradition. Bangneki or Hahn would be minor variations to spice them up, but I'd still consider them "go in spirit." Pair go, blitzkrieg go, one-color go would all be amusement tricks to have some fun. As for different sizes, all go. Maybe going smaller than 7 or 5 starts bending too much weight to the rulesets, though, but I'd still consider them full-fledged go.

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Geek of all trades, master of none: the motto for my blog mostlymaths.net

Actually (depending on ruleset) normal Go with non integer komi has a 3rd result (and 4th for integer komi): "No result" for quadruple kos and the like (e.g. that Lee Sedol Gu Li game last year), which is different from jigo. Also you have referee results like both players lose for disqualifications.

Jigo / no jigo creates different strategy for sure. However, the impact on strategy is only small because, in practise from the POV of human skill, the affects only (late) endgame decisions.

Komi / no komi produces also only a small impact because it shifts the threshold of where a player wins, and then every player still aims at winning. Ok, one must play a bit harder (riskier) as White and can afford to play softer as Black. Otherwise, the strategies are the same.

Hahn is not just different because of 10 different results. Much more importantly a) there is no equivalence of all win scores any longer, b) there are steps of different scores having equal results, so one can make 9 points mistakes but the 10th point is sharp, c) there is an upper score so that skills of creating very great scores (such as when killing a tremendous group to defend one's center moyo) are not rewarded appropriately. All these aspects affect strategy greatly throughout the game. To start with, I would never build a big center moyo under the Hahn system.

I think it's difficult to answer this type of question objectively. One could reasonably call of those games go (or at least some variant thereof).

One could also arbitrarily classify these into different levels of capturing the essence of the game. However, trying to rank the rule sets is perhaps as much about personal preference as it is political and controversial.

TIL - the Hahn system. Wow that's great. Combine this with bltz and you'd have an awesome TV show. The Weiqi X Games!

To answer OP - they are all go, imho.

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- Brady
Want to see videos of low-dan mistakes and what to learn from them? Brady's Blunders

To me, the game does not fundamentally change with the handicap, the komi, or the size of the board. The rules and the goal stay the same.

I feel it is a different but related game when the basic rules or the goal of the game is changed, so bangneki, hahn system (or e.g. capture go) I would not just call "go".

Pair go is a grey area. Though the rules or goal do not fundamentally change, there is an extra consideration during play along the lines of "will my partner understand my plan from this move?" or "does this sequence have difficult moves on the weaker player's turn?"