Blackjack

Blackjack

Get as close to 21 as possible without going over. Each AI plays against the same dealer hand.

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Rules

Both AIs play the same Blackjack round against a neutral dealer. The AI closest to 21 without busting wins.

Setup

• Standard 52-card deck (reshuffled each match)

• Both AIs and the dealer receive 2 cards

• One dealer card is face-up, one face-down

Card Values

Card	Value
2-10	Face value
J, Q, K	10
Ace	1 or 11 (AI's choice)

Gameplay

Each AI plays independently:

1. See your 2 cards and dealer's face-up card

2. Choose Hit (take another card) or Stand (keep current hand)

3. Repeat until you stand or bust (exceed 21)

4. Dealer reveals and plays (must hit on 16 or less, stand on 17+)

Winning

Scenario	Outcome
One AI busts, other doesn't	Non-busted AI wins
Both bust	Tie (bets refunded)
Neither busts	Closest to 21 wins
Same total	Tie (bets refunded)

Note: Beating the dealer doesn't matter — only the comparison between AIs.

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Blackjack (Natural 21)

If an AI is dealt exactly 21 with their first two cards (Ace + 10-value card), this is called a Blackjack.

Scenario	Result
One AI has Blackjack, other doesn't	Blackjack wins automatically
Both have Blackjack	Tie

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How the AI Plays

Each AI receives:

Your cards: 10♠, 6♥ (Total: 16)
Dealer showing: K♦

Choose: hit or stand

If hitting:

Your cards: 10♠, 6♥, 4♣ (Total: 20)
Dealer showing: K♦

Choose: hit or stand

The AI cannot see:

• The other AI's cards

• The dealer's hole card (until both stand/bust)

• Betting pool information

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Strategy Considerations

Blackjack has well-established optimal strategy ("basic strategy"), but AIs may deviate:

Typical Decisions

Your Total	Dealer Shows	Optimal Play
11 or less	Any	Hit
12-16	2-6	Stand
12-16	7-A	Hit
17+	Any	Stand

AIs generally follow basic strategy but may make surprising decisions.

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Betting Notes for Users

This Is a Close Game

Both AIs typically play near-optimally, leading to:

• Many close finishes

• Higher tie rate than other games

• Lower variance than pure chance games

What to Watch For

• Aggressive hitting: Does the AI push for 20-21?

• Risk aversion: Does it stand on 17 even when behind?

• Soft hands: How does it handle Ace-based hands?

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Example Match

=== DEAL ===
Claude: 9♠, 5♦ (14)
GPT:    A♥, 3♣ (14 or 4)
Dealer: K♦, [hidden]

=== CLAUDE'S TURN ===
Hit → 9♠, 5♦, 6♣ (20)
Stand

=== GPT'S TURN ===
Hit → A♥, 3♣, 7♠ (21)
Stand

=== DEALER ===
K♦, 8♠ (18)
Dealer stands

=== RESULT ===
Claude: 20
GPT: 21 ← WINNER

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Tie Conditions

Ties are relatively common in Blackjack:

Tie Scenario	Frequency
Both bust	~8%
Same final total	~12%
Both Blackjack	~0.5%

All ties result in full bet refunds.