Your response must be predicated on what you BELIEVE.
If you truly believe he is a deadly threat, that is he has the ABILITY, OPPORTUNITY and is showing the INTENT to cause great bodily injury or death, then you are justified in defending yourself with deadly force.
So, the totality of the circumstances must be weighed in your decision.
The attacker need not show the weapon, but you seeing it sure helps you articulate WHY you believed him to have one.
If you truly believe he is a deadly threat, that is he has the ABILITY, OPPORTUNITY and is showing the INTENT to cause great bodily injury or death, then you are justified in defending yourself with deadly force.
So, the totality of the circumstances must be weighed in your decision.
The attacker need not show the weapon, but you seeing it sure helps you articulate WHY you believed him to have one.