Who would win in a fight Darth Vader vs Robute Guilliman

GPT-5.5

Answer: Roboute Guilliman would most likely beat Darth Vader in a direct fight.

I maintain my previous position: Vader has dangerous win conditions through the Force, but Guilliman’s overall power scale, durability, speed, and wargear make him the more likely victor. The other models broadly agree, and none gave a reason to reverse course. The strongest added point is that Guilliman is not merely a bigger, stronger swordsman; his Armour of Fate, Iron Halo-style defenses, and Emperor’s Sword give him both survivability against exotic attacks and a one-hit-kill level offensive threat. That makes Vader’s lightsaber less decisive than it usually is. Vader’s best chance is to use the Force immediately: immobilize Guilliman, crush his armor or organs, choke him, or keep him at range. But Guilliman is a Primarch, a being built to fight superhuman warriors, daemon-empowered monsters, and psychic threats in a setting where battlefield lethality is extreme. It is not impossible for Vader to affect him, but it is unlikely to be clean or fast enough before Guilliman closes distance. Once the fight becomes melee or near-melee, Guilliman’s advantages compound: he is faster, stronger, more durable, better protected, and armed with weapons that can destroy Vader’s body and life-support systems outright. Vader is terrifying by Star Wars standards, but Guilliman is operating at a demigod-warrior scale that gives him the edge.

Claude Opus 4.7

Answer: Roboute Guilliman would win in a straight fight against Darth Vader.

All four models converged on the same answer, and reading through the others' arguments I see no reason to abandon my position — if anything, the consensus reinforces it. The reasoning across GPT-5.5, Gemini 3.1 Pro, and Grok 4.20 mirrors my own core argument: the physical, durability, and wargear gap between a Primarch and a Sith Lord is simply too vast for Vader to bridge through conventional combat. The only point worth refining is Vader's win condition. GPT-5.5 correctly emphasizes that the Force is Vader's real path to victory — precognition, telekinesis, and choke attacks could theoretically bypass Guilliman's physical advantages. This is the strongest case for Vader, and it's not nothing. However, Primarchs have demonstrated extreme resistance to psychic assault (Magnus the Red, a peer Primarch, is one of the most powerful psykers in the galaxy and Guilliman has stood against warp entities and daemon primarchs without being mind-controlled or telekinetically dismembered). Vader's Force output, while elite in his setting, is calibrated against humans and Jedi — not against a being whose willpower and psychic resilience were engineered to resist Chaos Gods. Once that win condition is neutralized or even just delayed, the fight collapses to physicals: an 8-9 foot transhuman demigod in artificer armour with an iron halo and a relic blade versus a 6'7" cyborg on life support. Guilliman closes the distance, tanks or parries the lightsaber with the Armour of Fate, and ends it. I'm holding my position.

Grok 4.20

Answer: Robute Guilliman would win in a fight against Darth Vader.

After reviewing the responses from GPT-5.5, Gemini 3.1 Pro, and Claude Opus 4.7, I maintain my original position because they all reach the same conclusion with overlapping and reinforcing arguments. Their analyses emphasize the immense physical, tactical, and durability gap that a Primarch operates within, which no new points have overturned. Claude Opus 4.7's detailed comparison of scale—highlighting Guilliman's survival against Fulgrim-level threats, the Armour of Fate's regenerative properties, and Primarch resistance to psychic assaults—particularly strengthens the case without contradicting my prior view. GPT-5.5 and Gemini 3.1 Pro similarly underscore that Vader's Force powers, while potent, face low odds against a being engineered for galaxy-spanning warfare against entities far beyond Star Wars norms. Vader's lightsaber and telekinesis remain dangerous, yet Guilliman's speed, Emperor's Sword, and experience closing distances against warp horrors make a decisive victory for the Primarch the most probable outcome. Cross-universe battles require assumptions, but the consistent consensus across models affirms that 40k's demigod tier simply outclasses this matchup.

Gemini 3.1 Pro

Answer: Roboute Guilliman would decisively defeat Darth Vader due to an insurmountable gap in physical speed, durability, and the sheer scale of Warhammer 40k power levels.

Seeing the consensus among the other models reinforces my initial assessment that Roboute Guilliman would comfortably defeat Darth Vader. The power scaling between Warhammer 40,000 and the Star Wars universe is fundamentally asymmetrical, and a Primarch sits near the absolute pinnacle of physical combat in a much more hostile, over-the-top setting. The other models rightly highlight that Guilliman's defensive capabilities, particularly the Armour of Fate and his Iron Halo energy shield, provide layers of protection that a lightsaber would struggle to penetrate before the fight concludes. In contrast, Vader's cybernetic life-support suit is a notorious physical weak point that Guilliman's transhuman processing speed and peerless tactical genius would immediately identify and exploit. While Vader's mastery of the Force—specifically telekinesis and Force choke—presents a theoretical threat, Guilliman regularly contends with reality-warping psychic attacks from Greater Daemons and Chaos Sorcerers. His immense willpower, sheer physical mass, and inherent Primarch resilience would almost certainly allow him to power through or resist Vader's Force holds long enough to strike. Ultimately, Vader simply lacks the superhuman reaction speed and durability to survive the inevitable close-quarters engagement. Guilliman would close the distance in a blur, and a single strike from the Emperor's Sword would bypass Vader's defenses and end the duel instantly.

Final Summary

The AI Roundtable reached a swift consensus that the Primarch operates on a power scale far beyond the Sith Lord. Claude Opus 4.7 pointed out that Vader is effectively a cyborg human bringing a knife to a fight against a nine-foot-tall transhuman demigod. While GPT-5.5 and Gemini 3.1 Pro noted Vader’s Force powers as a theoretical threat, Grok 4.20 argued that Guilliman’s experience resisting the literal gods of Chaos makes him functionally immune to a Sith's telekinesis.

All 4 models agreed