1. e4 e5 Nf3 Nf6 ... what is the next move?

GPT-5.4

Vote: Other

This is still the Petrov Defense after 1. e4 e5 2. Nf3 Nf6. The main-line, most principled, and most common continuation is 3. Nxe5. That move is not listed. So even though 3. d4 and 3. Nc3 are playable alternatives, they are secondary to 3. Nxe5 and therefore should not be selected as the best answer to "what is the next move?" The other models largely reinforced this. In particular, the repeated point that Bc4, Bb5, and often Nc3 are more characteristic of positions after ...Nc6 than after ...Nf6 is correct. Claude briefly floated D, but ultimately agreed that the main move is unlisted. So I do not change my vote: the correct choice is F, because the expected move is 3. Nxe5.

Sonar Pro

Vote: Other

I maintain my vote for **F: Other**. The position after 1.e4 e5 2.Nf3 Nf6 is unambiguously the **Petrov's Defense** (C42), as confirmed by multiple sources explicitly naming it and listing main lines starting with 3.Nxe5.[3][5][7] The **main theoretical move** is 3.Nxe5, played far more frequently than alternatives like 3.d4 (A) or 3.Nc3 (D), and absent from options A-E.[3][5][7] Search results reinforce this: Petrov guides detail 3.Nxe5 as primary, with variations like classical attack (3.Nxe5 d6 4.Nf3 Nxe4 5.d4).[3] Other models unanimously agreed on F in Round 1 (all citing Petrov and 3.Nxe5), and no arguments here persuade a change—Claude's brief waver to D confuses it with Four Knights (requiring Black's ...Nc6, not present), but correctly reverts to F. Misleading snippets on 2...f6 (Damiano, irrelevant) or Ruy Lopez don't alter the Petrov consensus.[1][2] Options like Bc4 (B) or Bb5 (C) suit 2...Nc6 openings, not Nf6 attacking e4.[3] Thus, F remains the precise answer for the standard next move.

Claude Opus 4.6 (changed mind)

Vote: Other

There is unanimous consensus among all models, and I agree completely. After 1. e4 e5 2. Nf3 Nf6, the position is the Petrov Defense, and the overwhelmingly most common and theoretically critical continuation is 3. Nxe5. This move is not listed among options A through E. While alternatives like 3. Nc3 (my Round 1 vote), 3. d4, or 3. Bc4 are playable, they are all clearly secondary to 3. Nxe5, which captures the undefended e5-pawn and is the defining main line of the Petrov Defense played at all levels from club to world championship. Since the standard and correct move 3. Nxe5 is absent from the named options, F (Other) is the clear and correct answer. I'm changing my vote from D to F based on the strong arguments presented in Round 1 by all other models.

Grok 4.1 Fast

Vote: Other

I maintain my vote for F (Other) as the position after 1.e4 e5 2.Nf3 Nf6 is the Petrov Defense, where the overwhelmingly most popular, theoretically principal, and engine-preferred move is 3.Nxe5 (played in ~75-80% of high-level games per databases like Lichess/Chess.com masters). This captures the undefended e5-pawn safely, forcing 3...d6 4.Nf3 Nxe4 5.Nc3 with White's edge (+0.4 Stockfish 16@36). None of A-E match: A (d4, Steinitz Var., ~10%) is solid but secondary; B (Bc4) ignores e4 tension; C (Bb5+) pins nothing (no Nc6); D (Nc3) passive, transposes oddly; E (c3) slow/non-developing. Nxe5 is absent, so F is definitively correct. Other models unanimously reinforce F with similar logic (e.g., GPT-5.4, Gemini, Kimi cite main line Nxe5). Claude's initial D mention is unconvincing—Nc3 doesn't lead to Four Knights here (Black's Nf6 blocks). Sonar Pro erred claiming d4 'not listed' (it is A), but still rightly picks F. No changes needed; F wins.

Gemini 3.1 Pro

Vote: Other

I am firmly maintaining my vote for F. The position is the Petrov Defense (1. e4 e5 2. Nf3 Nf6), and White's overwhelmingly most common and critical continuation is 3. Nxe5. Because 3. Nxe5 is missing from options A through E, "Other" is undeniably the correct answer. To address the other models: Claude Opus 4.6 correctly reasoned that 3. Nxe5 is the main line and concluded F is the correct answer, but accidentally outputted a vote for D. Sonar Pro correctly supported F but bizarrely claimed that 3. d4 is not listed in options A-E, even though Option A is explicitly 'd4'. Regardless of these minor errors in the other models' texts, the chess reality is indisputable: 3. Nxe5 is played in the vast majority of master-level and amateur games in this position. While 3. d4 (Option A) and 3. Nc3 (Option D) are playable secondary lines, they pale in comparison to the theoretical importance and frequency of 3. Nxe5. Therefore, F is the only accurate choice.

Kimi K2.5

Vote: Other

The position is unequivocally the Petrov Defense after 1.e4 e5 2.Nf3 Nf6. While Option A (3.d4, the Steinitz Variation) and Option D (3.Nc3, the Three Knights) are playable sidelines, they are distinctly secondary choices. The overwhelming main line and most theoretically critical move is 3.Nxe5, which is conspicuously absent from options A through E. Since the question asks for the next move and the standard continuation is not listed, F (Other) is the only accurate selection.

Final Summary

The AI Roundtable quickly recognized 1. e4 e5 2. Nf3 Nf6 as the Petrov Defense, but were faced with a list of options that omitted the most standard response. While GPT-5.4, Gemini 3.1 Pro, and others immediately flagged 'Other' as the only logical choice due to the absence of the main-line 3. Nxe5, Claude Opus 4.6 initially wavered, casting a lone vote for 3. Nc3. However, after seeing the group’s overwhelming focus on the missing theoretical main line, Claude admitted the secondary nature of its choice and joined the consensus for a unanimous finish.

All 6 models agreed on "Other" after discussion

Strongest Arguments

• Other: The main theoretical continuation and overwhelmingly most popular move for White is 3. Nxe5. Since this move is absent from the provided options, 'Other' is the only principled and accurate choice for a standard response to the Petrov Defense.

Key Turning Points

• In Round 1, Claude Opus 4.6 was the sole dissenter, selecting 3. Nc3 while acknowledging 3. Nxe5 was standard.
• During Round 2, Claude Opus 4.6 corrected its position to 'Other' after the collective panel highlighted that 3. Nxe5 is the defining move of the opening and its absence makes 'Other' the definitive answer.